19 95ApJS. . .98. .171V Honolulu, HI96822. MD 20742. 85726-6732. The AstrophysicalJournalSupplementSeries,98:171-217,1995May © 1995.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. 4 2 3 1 InstituteforAstronomy,University ofHawaii,2680WoodlawnDrive, DepartmentofAstronomy,University ofMaryland,CollegePark, HubbleFellow. KittPeakNationalObservatory,NOAO,P.O.Box26732,Tucson,AZ -1 -1 these resultssuggestthatlarge-scalenuclearwindsarecommon intheseobjectsandareanefficientwayofgetting galaxies inwhichwecoulddeterminetheradialvariations ofthe[Om]linewidthpresentbroaderprofilesin circumnuclear regionthanatthenucleus.Whencombined withpublisheddataonafewotherwell-studiedLIGs, than HiiLIGs.Complexopticaldeptheffectsmayalsoexplaintheseresultswithoutinvokingasmalleramount galaxies. Thedustdistributiongenerallyisconcentratedtowardthenucleus,inagreementwithoftenpeaky rid oftheobscuringmaterialinnuclearregion.Thespatially extendedLINERemissionobservedinmanyof objects. Nearly20%oftheLIGsinoursamplehavelinewidths largerthan600kms.Wefindthatmostofthe mining theextentofthiscontinuumsource. regardless oftheirnuclearspectraltypes.Contaminationby thecircumnuclearstarburstpreventsusfromdeter- evidence foryoungstarswhilegalaxieswithAGNsdonot. TheradialvariationsoftheHßandMgibabsorption Moreover, theabsorption-linedatamaysimplyreflectfactthatgalaxieswithpowerfulHiiregionsshow result maybealuminosityeffectratherthananrelatedtothedominantnuclearsourceofionization. support forthisscenariocomesfromthefactthatAGNsarefoundmorefrequentlyinadvancedmergersthan in HiiLIGs,suggestingthatAGNLIGsareatamoreadvancedstageofstellarevolutionthanHIILIGs.Further of objects:galaxieswithSeyfertemissionlinesmaybeatamoreadvancedstagedustdestruction/expulsion of activenuclei.Thismaybeduetoselectioneffectsorreflectrealphysicaldifferencesbetweentheseclasses characteristics (oneSeyfert2galaxyandtwoLINERs).Lownucleardustcontentappearstofavorthedetection distribution ofthemoleculargasobservedinthesegalaxies.Inverteddustprofileswhichnucleusappears features indicatethepresenceofastrongsourcefeatureless continuuminthenucleusofnearlyallLIGs, H iigalaxies(onlytwoSeyfertaredetectedinsystemswithwell-separatednuclei).However,thislast of dustinthenucleus. less dustythanthecircumnuclearregionareobservedinonlythreeLIGs,allofwhichhaveAGNemission-line suggest thatmostoftheLINERemissionintheseinfrared-selectedgalaxiesisproducedthroughshockionization rather thanphotoionizationbyagenuineactivenucleus. luminosity, reachingvaluesof62%and54%atthehighestobservedluminosities,respectively.Thefraction both thefractionofLIGswithAGNspectraandSeyfertsamongincreaseinfrared nuclear spectraltypes.Theemission-line,absorption-line,continuum,radio,andIRASpropertiesoftheLINERs stellar absorptionfeatures,circumnuclearstarburstactivityisacommonfeatureofLIGs,regardlesstheir often isafunctionofthedistancefromnucleus.Basedonemission-lineratiosandstrengths AGNs werefoundtobeofrelativelylowionizationlevelandthereforeclassifiedasLINER.Weconfirmthat This correctionisanimportantsourceoferrorsinsomepreviousstudies.Theemission-linespectramany tracted fromthenucleusoftheseobjects.Inthispaper,nucleardataarecombinedwithcircumnuclearmea- described thedata-takinganddata-reductionprocedurespresentedlinecontinuummeasurementsex- LINERs, ontheotherhand,isrelativelyconstantat~27%.Thesourceofionizationemission-linegas population inandoutofthenucleus.Thenuclearspectrathesegalaxieswereclassifiedas“Hnregion-like”or surements on23ofthesegalaxiestoinvestigatethepropertiesline-emittinggasandunderlyingstellar “AGN-like” usingalargenumberofline-ratiodiagnosticscorrectedfortheunderlyingstellarabsorptionfeatures. Mpc )wascarriedoutusingthePalomar5meterandUniversityofHawaii2.2mtelescopes.Kimetal.(1995 710 The [Oin]profilesofbothSeyfertandLINERLIGswere foundtobebroaderonaveragethanthoseofHn The HßandMgIbabsorptionfeaturesarestrongerinthenucleiofAGNs(especiallyamongLINERs)than The nuclearregionofSeyfertLIGsisfoundtobeslightlylessreddenedthanthattheLINERsandHn A spectroscopicsurveyofasample200luminousIRASgalaxies(LIGs:L>3X10;H=75kms“ ir0 © American Astronomical Society • Provided by theNASA Astrophysics Data System 23456 S. Veilleux,‘’'D.-C.Kim,D.B.Sanders,J.M.Mazzarella,andT.Soifer OPTICAL SPECTROSCOPYOFLUMINOUSINFRAREDGALAXIES. II. ANALYSISOFTHENUCLEARANDLONG-SLITDATA Received 1994April14;acceptedDecember2 ABSTRACT 171 adena, CA91125. tute ofTechnology,JetPropulsion Laboratory,Pasadena,CA91125. 6 7 5 PalomarObservatory,California Institute ofTechnology,320-47,Pas- Lir=L(8-1000^m). InfraredProcessingandAnalysisCenter,MS100-12,CaliforniaInsti- 19 95ApJS. . .98. .171V 1 is believedtobedeeplyembedded inthecoreoftheseobjects large infraredluminositiesoftheseobjects(seereviewHeck- gas inLIGsandtheroleofgalaxyinteractiontriggering the to determinethemainsourceofionizationline-emitting to berichinstar-formingmoleculargas(Sanders,Scoville, & and isthereforeinvisibleatoptical wavelengths(andpossibly line-emitting gasisimportant toemphasizehereastheformer radiation inthesegalaxiesand thesourceofionizationtheir cess isthedominantsourceofluminosityinLIGs. optically thickatwavelengths upto25/im;Condonetal. man 1991).Thedistinctionbetweenthesourceofinfrared Soifer 1991),themainissueshouldbetodeterminewhichpro- al. 1984),andgiventhatallluminousinfraredgalaxiesappear (e.g., Mrk231—Boksenbergetal.1977;NGC7469—Cutri et luminosity ofthebrightersources.Thereareseveralexamples dust-enshrouded activegalacticnuclei(AGNs;Rieke&Low galaxies (LIGs)mayprovideimportantcluestotheoriginof of knownnuclearstarburstssurroundinganactivenucleus (Harwitt etal.1987)havebeensuggestedtoexplainthelarge Condon etal.1991;Radford,Solomon,&Downes1991), intense starformation(Norman&Scoville1988;Rieke tions intriggeringthisactivity. these resultssuggestthatdetailedstudiesofluminousinfrared bly comesfromdustheatedbytheoldstellarpopulationoras correlation betweengalaxyinteractionandhighinfraredlumi- 1988a,b; Norrisetal.1988),andgalaxy-galaxycollisions 1972; DePoy,Becklin,&Wynn-Williams1986;Sandersetal. Leech etal.1989;Thronson1990).Scenariosinvolving a consequenceofstarformation(e.g.,Allen,Roche,&Norris powers themostluminousinfraredgalaxies(L^10L©) nuclear activityingalaxies,andtotheroleofgalaxyinterac- Wright 1985;Cutri&McAlarySandersetal.1987), Coupled withmorerecentobservationsthatsuggestastrong radio emissioninthenucleiofSeyfertandrelatedgalaxies. nosity (e.g.,Lonsdale,Persson,&Matthews,1984;Joseph served infraredluminositymaybecausallyconnectedtothe of awidevarietyextragalacticobjects,butalsothattheob- a dominantfeatureofthespectralenergydistribution(SED) ers etal.1989).ThepioneeringworkbyRieke&Low(1972) the dominantextragalacticpopulationinlocaluniverse, originally suggestedthatfar-infraredemissionmaynotonlybe at comparablebolometricluminosity(Soiferetal.1987;Sand- exceeding eventhespacedensitiesofopticallyselectedquasars emit thebulkoftheirradiationatfar-infraredwavelengths since thefar-infraredfluxinmostofweakersourcesproba- nature oftheirenergysource.Thedebateoftencentersonwhat fact, abovelog(L/L©)^11.5,thisclassofgalaxiesbecomes (e.g., Soiferetal.1984a,b,1986;Rieke&Lebofsky1986).In have revealedthatasignificantfractionofextragalacticobjects 1985; Elston,Cornell,&LebofskyLawrenceetal. 172 VEILLEUXETAL.Vol.98 Optical studiesgenerallyaddressthisquestionbyattempting Perhaps themostimportantquestionregardingLIGsis Surveys withtheInfraredAstronomicalSatellite(IRAS) Subject headings:galaxies:active—nucleistellarcontentHnregions—infrared:galaxies the ambientmaterialofhostgalaxy. these objectsisprobablyduetoshockionizationresultingfromtheinteractionofwind-acceleratedgaswith © American Astronomical Society • Provided by theNASA Astrophysics Data System 1. INTRODUCTION -1 _1 sions aresummarizedin§5. sible scenariostoexplainthedata.Finally,mainconclu- ergy sourcesinluminousinfraredgalaxiesanddescribingpos- implications ofthisanalysis,addressingthenatureen- tion aboutthespatialvariationsofvariousspectralparam- eters in23objectsofthesample(§3).In§4,wediscuss ysis ofthesenucleardata(§2)andalsoprovidesnewinforma- nuclear data.Thepresentpaperreportstheresultsofouranal- along withtabulationsofsometheresultsderivedfromthese effects. AnatlasofthenuclearspectrawaspresentedinPaperI from thesedataandthereforeminimizeaperture-related Mpc andq=0.5)wasusedtoextractthenuclearspectra Paper I).Aconstantlinearapertureof2kpc(H=15kms hereafter PaperI)and86objectsfromtheIRASWarmGalaxy IRAS galaxies,including114objectsfromtheBright tion windowof2kpc.Thesizethisimplies that ( 60¡im/100fim)colors,hereafterreferredtoastheWGSssee Survey (WGS)selectedonthebasisoftheir“warm”infrared Galaxy Survey(BGS;Soiferetal.1989;Sanders 2.2 mspectracovering5850-8870Àwereobtainedof200 ( sometimesupto~1/mi)ataresolutionof8-10AandMKO omar 5meterspectracoveringatleast3750-8000Á these dataprobablycoverregionsspanningalargerange in scopic surveyofalargesampleIRASgalaxies.Long-slitPal- dominantly fromregionsofsmaller opticaldepths(seediscus- as theobservedlineandcontinuumemissionwillcome pre- ford etal.1991).AsdescribedindetailPaperI, the compact regionsofdiameterlessthan1kpc(e.g.,Scovilleet al. and radiosurveyshaveshowntheexistenceoflargequantities attempt toremedythissituationwehavecarriedoutaspectro- line andcontinuumdiagnosticsusedintheiranalysis.Inan been thesmallsizeoftheirsamplesorlimitednumber derlying stellarabsorptionfeatures. Theobservedintensityra- is theemission-lineBalmer decrement correctedfortheun- sion ofLeechetal.1989). nuclear datawillthereforebelowerlimitstothetrueextinction optical depths.Theextinctionmeasurementsderivedfrom the “nuclear” dataofoursurveywerederivedusingafixedextrac- of dustandmoleculargasinLIGs,generallyconcentrated into will bereviewedinthediscussionofourresults(§4). gas andunderlyingstellarpopulationaregoodprobesofthe follow inthepresentstudy.Theweaknessesofthisassumption central energysource.Thisisalsotheapproachthatwewill assuming thatthephysicalcharacteristicsofcircumnuclear 0 0 1995a,b), hereafterreferredtotheBGSs(seeKimetal.1995, 1986, 1989,1991;Solomon,Radford,&Downes1990;Rad- 1991). Opticalstudiesinferthenatureofenergysourceby The primarydustindicatorused inthepresentinvestigation We startthissectionwithacautionarynote.Far-infrared A majorlimitationofpreviousopticalstudiesLIGshas 2. RESULTSFROMTHENUCLEARDATA 2.1. Dust 19 95ApJS. . .98. .171V 4 4-3 be steeperthanthecalculatedvalues,withdifferencebeing tios ofthetwostrongestBalmerlines,HaandH0,werecom- these twodatasetsaredrawnfromthesamedistributionis0.01. analysis becauseoftheirintrinsicweaknessandthey attributed tointerstellarextinction.Stellarabsorptionfeatures pared tothecalculatedvalues.Invariably,theywerefound galaxies (caseBBalmerrecombinationdecrementforT=10 tion. WeadoptedanintrinsicHa/H0ratioof2.85forHn ler &Mathews(1972)wasused.Allofthenarrow-linegalaxies lines. TheWhitfordreddeningcurveasparameterizedbyMil- are morestronglyaffectedbytheunderlyingstellarabsorption No attemptwasmadetoincludethelowerBalmerlinesin account inthemeasurementprocedure(seePaperI,§5.2). underlying theemissionlinesofHaandH0weretakeninto listed ascolorexcesses,E(B-V\incolumn(3)ofTable1. axies basedontheiremission-linespectrum.Themethodused in oursamplewereclassifiedasHn,LINER,orSeyfert2gal- with typicalvaluesmeasuredinactivegalaxies.Dahari&De WGSs areshowninFigure1.ThemedianE(B—V)forobjects The distributionsofE{B-V)forgalaxiesintheBGSsand Note thatthesenumbersincludeextinctionduetotheGalaxy. kell& Ferland1984). K and=10cm)3.10forAGNs(Ferland&Netzer for theclassificationwillbediscussedindetailnextsec- E^B -V)=0.52andevensmallerindiskHnregions:E(B- tively. Similarly,typicalreddeninginnuclearHnregionsis in theBGSsandWGSsare1.130.91,respectively.AKol- and 0.69forSeyfert1,2,starburstgalaxies,respec- Robertis (1988)foundmedianE{B-V)valuesof0.37,0.56 mogorov-Smimov (K-S)testshowsthattheprobability are considerablysmallerthanthecolorexcessesmeasuredin No. 1,1995 1983; Péquignot1984;Binette,Dopita,&Tuohy1985;Gas- V) =0.36(Kennicutt,Keel,&Blaha1989).Allofthesevalues are slightlymorereddenedthanthe WGSsgalaxies. and WGSs{short-dashedline)galaxies ofoursample.TheBGSsgalaxies The amountsofreddeningderivedfromthismethodare The amountofreddeningfoundinLIGscanbecompared Fig. 1.—Distributionofthecolor excessesfortheBGSs{solidline) © American Astronomical Society • Provided by theNASA Astrophysics Data System E(B-V) LUMINOUS INFRAREDGALAXIES.II. The correlationbetweenthereddening andthestrengthof LIGs isofinterstellarorigin, in contrasttotheMgIbfeature. strongly suggeststhatmostof theNaiDabsorptionfeaturein D andMgIbequivalentwidths arenotcorrelated.Thisresult A(H i)tohavelargeemission-linedecrements. the presentstudy:wefindatendencyforobjectswithlarge line Balmerdecrementin12ofthesegalaxieswasmeasured in the infraredluminosityforanyclassofobjects.Mirabel & in absorptionagainstthenuclearradiosource.Theemission- of 18LIGsbymeasuringthestrengthH121cmlineseen we comparethecolorexcessesofLINERsandHnobjects. galaxies andLINERsaredrawnfromthesamedistribution is The Seyfert2galaxiesareslightlylessreddenedthantheothergalaxies. Sanders (1988)derivedtheHIcolumndensitiesinnuclei axies arecomparedwiththoseofHngalaxies,and0.1when dicate thattheprobabilitycolorexcessesofSeyfert2 only 0.009.Itis0.09whenthecolorexcessesofSeyfert2 gal- reddened thantheLINERs[E(B-F)=1.14].K-Stestsin- H ilLIGs[E(B—V)=0.99],whichmaythemselvesbeless of Seyfert2LIGs[E(B-V)=0.72]tobelessreddenedthan more detail).Theremaybeatendencyfortheopticalspectra lected objects.Figure2presentsthedistributionofE{B—V) for thevarioustypesofgalaxiesinsample(see§2.2 LIG andconfirmtheimportanceofdustininfrared-se- Figure 3showsthat,contrary toellipticalgalaxies,theNai No significantcorrelationwasfoundbetweenE(B-V)and Fig. 2.—Distributionofthecolorexcessesasafunctionspectraltypes. E(B-V) 173 19 95ApJS. . .98. .171V ♦UGC 2369 *IR 02438+2122 ♦UGC 2238 ♦NGC 1083 NGC 1056 NGC 1050 ♦NGC 1068 *NGC 873 *NGC 695 ♦III Zw35 *NGC 660 *IR 01364-1042 *NGC 520 *UGC 903 ^MCG+02-04-025 *MCG-03-04-014 *IC 1623 *UGC 556 Name *NGC 232 *NGC 23 ♦MCG-02-01-051 *NGC 34 (i) Observed andDereddenedLineRatios,Densities,SpectralClassification—7/L45BrightGalaxies © American Astronomical Society • Provided by theNASA Astrophysics Data System SE N N N H ß 25.7: 29.5: 6.17: 10.0; 11.0: Ho, 6.92 3.10 3.10 2.85 3.10 6.61 2.85 5.50 2.85 6.17 8.71 3.89 3.10 2.85 2.85 3.10 3.10 3.10 9.33 2.85 7.94 2.85 32.4 8.71 16.6 8.51 3.47 3.98 3.10 2.85 2.85 2.85 2.85 9.77 6.92 3.10 2.85 4.27 2.85 2.85 2.85 5.89 10.5 2.85 24.5 (2) E(B-V) 0.68: 2.13: 2.25: 1.18; 1.27: 0.88 0.65 0.85 0.77 0.31 1.13 1.03 0.20 0.32 0.74 1.69 2.37 1.18 0.40 0.90 1.12 1.10 2.08 1.15 1.31 (3) -0.61: -0.59: -0.40 -0.35 -0.29 -0.26 [OUI] [Nil][SII][OI][Oil]6731 -0.14 -0.10 -0.51 -0.33 -0.27 -0.48 -0.50 -0.55 -0.07 -0.06 -0.01 -0.42 -0.13 -0.37 -0.20 -0.14 -0.15 -0.20 -0.42 -0.38 0.41 0.51 0.20 0.30: 0.12; 0.07; 0.21: 0.27: Hß 0.28 1.16 1.19 0.29 0.34 0.42 0.12 0.36 0.37 0.10 0.18 0.24 0.50 0.60 (4) -0.02: -0.01: -0.28 -0.28 -0.21 -0.41 -0.40 -0.20 -0.42 -0.41 -0.33 -0.24 -0.23 -0.33 -0.35 -0.35 -0.72 -0.72 -0.16 -0.15 -0.35 -0.34 -0.41 -0.40 -0.29 -0.28 -0.56 -0.56 -0.23 -0.67 -0.67 -0.22 -0.13 -0.14 -0.43 -0.36 -0.35 -0.43 -0.23 -0.23 0.10: 0.11: 0.13 0.14 0.02 0.01 0.00 0.01 0.10 0.11 H a (5) TABLE 1A -0.54: -0.47 -0.50 -0.43 -0.49: -0.47: -0.23: -0.19: -0.67 -0.65 -0.44 -0.42 -0.46 -0.43 -0.62 -0.60 -0.64 -0.61 -0.80 -0.77 -0.52 -0.51 -0.27 -0.31 -0.37 -0.32 -0.33 -0.26 -0.42 -0.31 -0.46 -0.54 -0.51 -0.66 -0.63 -0.63 -0.62 -0.58 -0.59 -0.28 -0.67 -0.58 -0.33 -0.49 174 -0.71 -0.72 -0.71 -0.60 -0.27 -0.51 Ha (6) -0.81: -0.70: -0.89: -0.92: -0.46: -0.53: -1.34: -1.40: -1.65 -0.97 -1.25 -1.70 -1.09 -1.28 -1.34 -1.38 -1.60 -1.69 -1.64 -1.75 -1.23 -1.28 -1.33 -1.35 -0.68 -0.74 -1.12 -1.21 -1.15 -1.27 -1.36 -1.55 -1.45 -0.84 -0.93 -1.41 -1.61 -1.66 -1.56 -1.43 -0.90 -1.31 -1.37 -1.75 -1.50 -1.54 -1.03 -1.41 -1.44 -1.73 Ha (7) -1.21: -1.30: [OIII] 6716 1.90 0.69 1.62 0.71 0.73 0.25 (8) (9) 0.28: 0.28: 0.74: 0.74: 0.63 0.63 0.76 0.76 0.91 0.91 0.71 0.71 0.69 0.65 0.68 0.65 0.91 0.91 0.68 0.74 0.68 0.76 0.83 0.78 0.79 0.71 0.71 0.83 1.00 0.81 0.83 0.85 0.83 0.91 0.91 0.55 0.55 0.95 0.95 1.00 N (10) (11)(12)(13)(14) e 390 H 110 H 410 590 230 H 390 H 480 H 110 260 H 160 H 250 80: H 20 H 30 H 40 H a H a H a H a H a S2 [Nil] [SII][OI]Adopt S2 L L H L L L L L Spectral Types H L L L L L L L S2 H: L: S2 H: H H H H H H H H H L H H H H H L L L L 19 95ApJS. . .98. .171V UGC 5101 UGC 4881 NGC 2785 IR 08572+3915 MCG+08-18-012 NGC 2623 IR 08339+6517 NGC 2388 IR 05189-2524 IR 05186-1017 NGC 1797 IC 398 ESO 485-G003 ESO 484-G036 NGC 1614 ESO 550-IG025 UGC 2982 IR 03359+1523 NGC 1377 NGC 1266 NGC 1204 NGC 1143/4 Name *UGC 2403 (i) American Astronomical Society •Provided bythe NASA Astrophysics Data System SW NE N 24.0: 29.5: 5.75: 23.4: Hor H« — E(B-V) 8.91 3.10 9.55 9.12 3.10 3.10 3.10 2.85 2.85 2.85 4.27 3.10 3.10 8.71 3.10 3.10 9.12 3.10 9.55 3.10 3.10 3.10 4.90 23.4 12.6 2.85 2.85 2.85 2.85 2.85 5.75 2.85 14.8 1.00 2.85 7.59 2.85 2.85 5.37 2.85 11.0 1.00 18.6 1.00 17.4 15.1 (2) 0.62: 2.27: 2.03: 2.05: 0.40 0.71 0.99 0.65 0.47 2.04 1.15 1.21 1.50 1.66 1.17 1.36 1.13 1.13 1.89 1.09 1.74 1.67 (3) -0.55: -0.49: [OIII] [Nil][SII][OI][Oil]6731 -0.26 -0.23 -0.18 -0.33 -0.37 -0.29 -0.89 -0.82 -0.85 -0.80 -0.54 -0.50 -0.17 -0.12 -0.65 -0.56 -0.22 -0.17 -0.51 -0.45 -0.47 -0.38 -0.35 -0.27 0.07 0.17: 0.08: 0.11: 1.53: 1.63 Wß 0.36 0.46 0.31 0.37 0.22 0.24 0.03 0.06 1.11 1.13 (4) TABLE 1A—Continued -0.23 -0.22 -0.15 -0.14 -0.20 -0.19 -0.23 -0.22 -0.38 -0.37 -0.22 -0.01 -0.59 -0.58 -0.24 -0.24 -0.28 -0.27 -0.46 -0.22 -0.46 -0.20 -0.20 -0.11 -0.11 -0.38 -0.37 -0.46 -0.46 -0.11 -0.28 -0.27 -0.10 0.59: 0.12 0.13 0.09 0.00 0.02 0.04 0.03 0.04 0.10 0.57 0.57 0.34 0.34 H« (5) 175 -0.58 -0.52 -0.49 -0.47 -0.35 -0.54 -0.45 -0.38 -0.56 -0.54 -0.42 -0.39 -0.22 -0.62 -0.61 -0.58 -0.63 -0.60 -0.22 -0.45 -0.62 -0.72 -0.66 -0.23 -0.17 -0.32 -0.56 -0.53 -0.15 -0.72 -0.69 -0.40 -0.45 -0.42 -0.51 -0.45 -0.72 -0.70 -0.40 -0.61 -0.56 -0.44 0.31: 0.04 0.06 0.21 0.23 Ha (6) -1.25: -1.35 -0.95 -1.05 -1.34 -1.23 -1.28 -1.30 -1.24 -1.31 -1.26 -1.31 -1.34 -0.99 -1.82 -1.84 -1.22 -1.55 -1.61 -1.70 -0.90 -1.01 -1.78 -1.04 -1.11 -1.16 -1.71 -1.70 -0.46 -0.49 -1.10 -1.19 -1.33 -1.41 -0.70 -1.59 -1.66 -1.12 -0.81 -0.92 -1.66 -1.73 -0.98 -1.62 -1.73 -0.72 Ha (7) [OUI] 6716[NII][Sil][OI]Adopt -0.10 0.20 0.32 0.15 1.06 0.18 (8) (9)(10)(11)(12)(13)(14) 0.87: 0.87: 1.32: 1.35: 1.17: 1.17: 1060: 0.41 0.41 0.76 0.76 0.81 0.81 0.85 0.85 0.65 0.65 0.76 0.60 0.65 0.74 0.74 0.89 0.89 0.58 a 0.83 0.83 240 0.76 110 0.95 0.98 510 0.39 0.39 a 0.98 0.98 530H 0.85 0.85 0.74 0.74 0.63 1.02 640 1.02 1.02 1.02 L 1630: N 310: c 370 210 280 660 110 290 100 90 S2 S2 H H H L H H H H H L H L L H L H L L H L L H L H Spectral Types H H H: H: H: S2 S2 H: L: L: L: H H H H H H H H L L L L 19 95ApJS. . .98. .171V MCG-02-33-098 UGC 8058 NGC 3110 *NGC 5104 *UGC 8387 *UGC 8335 *IC 860 IC 3908 MCG+00-29-023 NGC 3597 NGC 3508 Name *NGC 5218 *NGC 4922 *NGC 4666 *IR 12224-0624 *UGC 6436 *IR 10565+2428 *NGC 5257/8 *NGC 5256 (i) © American Astronomical Society • Provided by theNASA Astrophysics Data System NW NW SW NE NE SE SE W W W W E E 4.17; 22.4: H % Q 6.46 3.10 3.10 3.10 3.10 3.10 6.31 3.10 3.10 9.12 4.68 6.92 3.24 3.10 6.31 3.10 3.89 3.10 2.85 2.85 7.94 7.08 2.85 2.85 12.3 2.85 2.85 12.3 1.00 2.85 2.85 21.4 2.85 2.85 2.85 5.50 2.85 1.00 2.85 16.2 11.2 1.00 1.00 7.59 7.76 18.2 12.3 2.85 (2) E(B-V) 0.30; 1.99: 0.83 0.83 0.22 0.79 0.99 0.49 0.89 0.72 0.91 0.66 0.13 1.39 1.46 1.28 1.02 2.03 1.18 1.75 1.86 1.46 (3) -0.14; -0.13; [OIII] [NH][SII][OI][Oil]6731 -0.30 -0.16 -0.10 -0.01 -0.20 -0.16 -0.20 -0.13 -0.36 -0.60 -0.36 -0.31 -0.53 -0.44 -0.65 -0.42 -0.39 -0.30 -0.21 -0.95 -0.91 -0.12 -0.12 -0.19 -0.16 0.04: 0.14: % 0.47 0.14 0.16 0.03 0.11 0.43 0.62 0.65 0.16 0.08 0.12 0.07 0.14 (4) TABLE 1A—Continued -0.39 -0.14 -0.14 -0.34 -0.33 -0.59 -0.50 -0.49 -0.25 -0.20 -0.20 -0.07 -0.06 -0.07 -0.06 -0.18 -0.18 -0.39 -0.59 -0.49 -0.49 -0.24 -0.23 -0.32 -0.19 -0.37 -0.46 -0.45 -0.45 -0.45 -0.17 -0.32 -0.31 -0.39 -0.38 -0.46 -0.46 -0.25 -0.31 -0.18 -0.37 0.89 0.11 0.05 0.05 0.11 (5) -0.61 -0.50 -0.47 -0.41 -0.40 -0.67 -0.46 -0.43 -0.74 -0.68 -0.65 -0.62 -0.58 -0.56 -0.44 -0.33 -0.33 -0.33 -0.29 -0.32 -0.26 -0.36 -0.65 -0.55 -0.52 -0.65 -0.53 -0.50 -0.63 -0.55 -0.55 -0.53 -0.59 -0.54 -0.66 -0.63 -0.57 -0.56 -0.22 -0.19 -0.65 -0.64 -0.69 -0.51 176 0.62 0.09 Ha (6) -1.65: -1.66 -1.27: -1.24: -1.60 -1.72 -1.57: -1.62: -1.23: -1.29: -1.21; -1.26; -1.55: -1.56: -2.65 -2.67 -1.29 -0.61: -0.91 -0.92 -0.94 -1.22 -1.28 -1.11 -1.18 -1.10 -1.15 -1.54 -1.25 -0.30: -0.89 -0.96 -1.04 -1.14 -1.01 -1.45 -1.50 -0.06 -1.63 -1.26 -1.34 -1.38 -1.47 -1.67 -1.68 -0.07 0.02 H [OIII]6716 a (7) (8)(9) -0.02 0.17 0.07 0.33 1.23: 1.23: 0.68 0.41 0.41 0.95 0.93 0.81 0.81 0.74 0.65 0.65 0.68 0.68 0.69 0.93 0.95 0.68 0.91 0.74 0.91 0.69 0.69 0.69 0.83 0.83 1.05 0.83 0.83 1.05 0.85 0.85 1.10 1.12 1.00 1.00 1220: N (10) (11)(12)(13)(14) e 690 410 410 850 500 220 590 230 250 260 90 10 [Nil] [SII][OI]Adopt SI S2 H H L H H H H L H H H H H H L H L L L L L L H L Spectral Types H L L L L L L L L L 51 H: H: H: 52 L: L: H H H H H H H H H H L L L L L 19 95ApJS. . .98. .171V *NGC 6181 *MCG-1-01-42-088 *IR 16164-0746 *NGC 6090 *IR 15335-0513 UGC 9913 *NGC 5953 *NGC 5936 *IR 15250-1-3609 *1 Zw107 Zw 049.057 *UGC 9618 *NGC 5734 ♦IR 14348-1447 *NGC 5676 *NGC 5653 *Zw 247.020 *NGC 5430 *UGC 8696 *NGC 5257/8 Name a) © American Astronomical Society • Provided by theNASA Astrophysics Data System SW SW NE NE W N E S n ß 16.6: 74.1; 17.8: 42.7: 6.31 3.10 2.85 Ha 2.85 3.10 12.3 4.68 2.85 5.01 2.85 2.85 3.10 3.10 3.10 6.61 1.00 7.59 2.85 8.13 3.10 12.6 2.85 3.10 3.10 9.77 3.10 8.51 2.85 3.10 9.12 7.24 6.74 17.8 2.85 5.50 8.13 12.9 2.85 2.85 3.10 9.12 2.85 12.0 2.85 2.85 1.00 (2) E(B-V) 3.10; 1.68: 1.75: 2.73: 0.80 0.58 0.49 1.47 0.89 0.76 0.84 1.50 1.06 1.76 0.86 0.66 1.15 1.02 1.43 1.16 1.44 1.05 1.07 (3) -0.72: -0.68: -0.25: -0.17: -0.84: -0.71: -0.73; -0.67; -0.57 -0.50 -0.35 -0.33 -0.62 [OUI] [Nil][SII][01][Oil]6731 -0.55 -0.04 -0.06 -0.02 0.09: -0.35 -0.64 -0.32 -0.68 -0.46 -0.39 -0.51 -0.45 0.79; 0.95; 0.01 0.10 0.08 n H 0.26 0.30 0.11 0.15 0.01 0.06 0.14 0.13 0.09 0.13 0.20 ßa 0.45 0.50 (4) (5)(6) TABLE 1A—Continued -0.33 -0.33 -0.29 -0.28 -0.48 -0.48 -0.46 -0.46 -0.11 -0.11 -0.22 -0.22 -0.33 -0.33 -0.26 -0.25 -0.12 -0.11 -0.55 -0.54 -0.09 -0.08 -0.21 -0.20 -0.20 -0.21 -0.23 -0.36 -0.22 -0.43 -0.26 -0.44 -0.42 -0.42 -0.13 -0.12 -0.31 -0.30 -0.25 0.00 0.01 0.07 0.08 0.22 0.29 0.23 0.01 0.02 -0.63 -0.61 -0.47 -0.36 -0.51 -0.31 -0.79 -0.78 -0.65 -0.64 -0.34 -0.29 -0.04 -0.40 -0.37 -0.07 -0.65 -0.61 -0.45 -0.43 -0.56 -0.59 -0.35 -0.29 -0.60 -0.52 -0.48 -0.46 -0.43 -0.57 -0.54 -0.51 -0.48 -0.44 -0.66 -0.71 -0.64 177 -0.63 -0.74 -0.66 -0.69 -0.16 -0.64 -0.59 -0.56 -0.24 -0.21 -1.41: -1.55: -1.68: -1.74: -0.61 -1.40 -1.47 -1.74 -1.77 -0.69 -1.73 -1.75 -0.69 -0.77 -0.78 -0.70 -1.19 -1.24 -1.54 -1.62 -1.13 -1.16 -1.42 -1.47 -1.07 -1.15 -0.85 -0.90 -1.10 -1.14 -1.02 -1.09 -1.90 -1.94 -1.52 -1.49 -1.59 -1.54 -0.62 -0.85 -0.90 H [OIII]6716 (7) (8)(9) a 1.02: 1.02: 0.68: 0.68: 0.91 0.91 0.89 0.89 0.78 0.51 0.78 0.65 0.51 0.00 0.85 0.85 0.95 0.98 0.68 0.68 0.69 0.83 0.83 0.65 0.71 0.60 0.62 0.00 0.63 0.78 0.79 0.76 0.76 1.15 1.15 660: H Ne (10) (11)(12)(13)(14) 400 H 350 H 150 H 280 510 240 980 160 120 30 a L a S2 a [Nil] [Siq[OHAdopt H H L H L H H H H H L L H L L L L H L Spectral Types H L H L S2 H: H L: L: L: H L: H H H L H H L H H H H L L L 19 95ApJS. . .98. .171V *ESO 602-G025 *ESO 534-G009 *IC 5179 *NGC 7130 *ESO 343-IG013 *ESO 286-IG019 *Zw 448.020 *NGC 6926 *IR 19297-0406 *ESO 593-IG008 *NGC 6701 *NGC 6670 *IR 18293-3413 *NGC 6621 *IR 17208-0014 *IR 17138-1017 *IR 17132+5313 Name *NGC 6285/6 *NGC 6240 (i) American Astronomical Society •Provided bythe NASA Astrophysics Data System NW NW SE SE W W N N E E S S n ß 5.75: 15.9: H 3.10 3.10 9.12 8.13 8.77 8.91 3.89 2.85 2.85 2.85 5.01 3.10 10.7 2.85 2.85 2.85 2.85 9.12 3.10 7.08 2.85 2.85 13.8 2.95 2.85 3.10 a 2.85 10.0 19.5 2.85 3.10 2.85 4.90 3.10 3.10 18.2 16.6 2.85 2.85 11.2 18.2 1.00 2.85 2.85 1.00 11.0 7.24 15.9 (2) E(B-V) 0.63: 1.63: 0.57 0.31 0.92 1.13 1.24 1.04 1.18 1.07 0.00 1.57 1.16 1.26 1.94 0.55 1.85 0.95 1.76 1.30 1.87 1.26 1.65 (3) -0.63: -0.69: -0.92: -0.83: -0.33 -0.38 -0.06 -0.04 -0.38 -0.41 -0.11 -0.23 -0.16 -0.21 [OUI] [Nil][SII][OI][Oil]6731 -0.15 -0.19 -0.13 -0.07 -0.14 -0.19 -0.04 -0.62 -0.53 -0.43 -0.37 -0.14 -0.05 -0.38 -0.33 -0.25 -0.19 -0.28 -0.36 0.27: 0.30: 0.80: 0.88: H/? 0.02 0.38 0.44 0.30 0.31 0.07 0.15 (4) TABLE 1A—Continued -0.18 -0.18 -0.52 -0.51 -0.04 -0.03 -0.29 -0.29 -0.27 -0.26 -0.41 -0.67 -0.41 -0.67 -0.23 -0.23 -0.26 -0.25 -0.31 -0.31 -0.13 -0.12 -0.43 -0.42 -0.43 -0.42 -0.34 -0.41 -0.33 -0.22 -0.22 -0.40 -0.30 -0.35 -0.35 -0.08 -0.08 -0.32 -0.32 0.45; 0.45; 0.30 0.30 0.11 0.12 0.47 0.10 0.09 (5) (6) -0.70 -0.63 -0.32 -0.41 -0.39 -0.44 -0.67 -0.67 -0.28 -0.43 -0.40 -0.40 -0.78 -0.77 -0.46 -0.16 -0.47 -0.49 -0.11 -0.52 -0.52 -0.48 -0.50 -0.23 -0.23 -0.46 -0.59 -0.53 -0.68 -0.62 -0.57 -0.63 -0.64 -0.59 -0.44 -0.50 -0.22 -0.22 -0.49 -0.18 -0.29 -0.27 0.04 0.06 0.60 0.56 0.04 0.09 -1.43: -1.17 -0.39 -0.42 -1.23 -1.37 -1.43 -0.59 -1.31 -1.37 -1.25 -1.28 -1.16 -1.21 -1.66 -1.03 -1.08 -1.67 -0.40 -0.48 -1.10 -1.18 -1.44 -1.50 -1.00 -1.00 -1.23 -1.29 -1.37 -1.47 -1.56 -1.65 -1.56 -1.28 -1.30 -1.47 -1.35 -1.39 -1.63 -1.66 -0.81 -0.87 -1.24 -0.51 -1.29 -0.43 -0.65 H [OUI]6716 a (7) (8)(9) 0.95: 0.98: 0.72 0.79 0.79 0.72 0.65 0.65 0.69 0.69 0.69 0.71 0.63 0.65 0.83 0.83 0.69 0.69 0.79 0.81 0.63 0.65 0.89 0.89 0.85 0.85 0.71 0.71 0.83 0.69 0.83 0.71 0.71 0.74 0.93 0.93 510: N (10) (11)(12)(13)(14) e 180 230 200 HL 360 280 H 450 H 250 H 60 20 10 10 40 H 40 20 H 70 a a a H [Nil] [SII][OI]Adopt S2 H H H L H L H H H LH: L H L L L L L Spectral Types H L H: H: S2 H: H: L: H H H H H H H H H H L L L 19 95ApJS. . .98. .171V 10 -15 the continuumcolorsofAGN ispredominantlyintrinsic, other. Indeed,ifthecontinuum colorsareassumedtobered- while inHIIgalaxiesalarge fractionofthescatterisdueto galaxies, andLINERs,respectively).Asimilareffectis ob- variations intheamountofreddening fromoneobjecttothe tinuum determinedbytheratioofcontinuumlevels at Seyfert 2galaxies,respectively. Thissuggeststhatthescatterin served whenEW(NaID)isreplacedbythecolorofcon- itous is5X10“,0.0002,and0.01fortheHngalaxies,Seyfert galaxies (theprobability,P[null],thatthiscorrelationisfortu- among theLINERsandSeyfert2objectsthan H n tween E(B—V)andEW(NaiD)isconsiderablyweaker AHM89). Figure4indicates,however,thatthecorrelation be- 6563 and4861A(C6563/C4861,Fig.5):weobtainP[null] smaller sampleofArmus,Heckman,&Miley(1989,hereafter Na IDfeature.Qualitativelysimilarresultswerefoundin the Na IDfeature(Fig.4)confirmstheinterstellaroriginof = 2X10,0.003,and0.8fortheHngalaxies,LINERs, and *MCG+03-60-036 IR 23365+3604 Name *NGC 7771 *NGC 7714 *NGC 7679 *Zw 453.062 *NGC 7591 *Zw 475.056 *NGC 7469 *IR 22491-1808 *NGC 7674 *NGC 7592 *UGC 12150 a) © American Astronomical Society • Provided by theNASA Astrophysics Data System W H/J 3.10 8.32 3.10 3.55 3.89 3.10 2.85 5.25 21.4 3.10 3.10 6.31 9.55 6.46 2.85 2.85 2.85 4.37 3.10 3.10 7.41 17.4 2.85 2.85 2.82 2.85 12.3 2.85 11.0 19.5 (2) E(B-V) 0.61 0.88 0.21 0.23 0.71 2.03 0.42 0.00 0.81 1.09 1.73 1.39 1.13 1.27 1.93 (3) LUMINOUS INFRAREDGALAXIES.II. [oiiq [Nil][sii][oq[oiq673i -0.46 -0.41 -0.20 -0.17 -0.08 -0.30 -0.26 -0.14 -0.28 -0.12 -0.28 -0.19 -0.15 -0.46 -0.55 0.02 0.18 0.19 0.60 0.68 0.51 0.04 0.55 0.10 0.62 0.67 0.03 0.09 1.06 1.07 (4) TABLE 1A—Continued -0.27 -0.27 -0.44 -0.44 -0.33 -0.32 -0.18 -0.43 -0.43 -0.02 -0.18 -0.23 -0.11 -0.50 -0.49 -0.15 -0.14 -0.01 -0.74 -0.24 -0.11 -0.02 -0.02 -0.74 -0.37 -0.37 -0.18 -0.17 0.08 0.09 Ha (5) -0.60 -0.59 -0.57 -0.57 -0.38 -0.37 -0.72 -0.41 -0.44 -0.35 -0.71 -0.53 -0.64 -0.41 -0.37 -0.58 -0.55 -0.63 -0.39 -0.59 -0.56 -1.34 -0.62 -0.60 -0.56 -0.32 -0.28 -1.34 -0.54 -0.48 Ha (6) dressed usingdiagnosticlineratios. the presentandnextfoursections. Here,theissueofmain source ofionizationthe line-emitting gasinLIGsisad- with emissionlines.Thecharacteristicsoftheselinesare im- source ofionization.Allthese propertieswillbediscussedin sity structureofthegas,itstemperature,kinematics, and portant indicatorsoftheconditionsthermalgasinthese reddening correctionswhilethescatterincontinuum col- HII galaxiesandinLINERsis30%-50%narrowerthanbefore that thedistributionof¿/¿reddenedcontinuumcolors in dened bythesameamountasemission-linegas,wefind objects. Theemissionlinescanbeusedtodeterminetheden- ors ofSeyfertgalaxiesbasicallyremainsthesame(see§2.8 ). -1.95; -1.98; The broadspectralcoverage of ourdataallowedustouse Nearly allofthegalaxiesinoursamplepresentaspectrum -1.55 -1.60 -1.35 -0.98 -1.25 -1.13 -1.18 -1.74 -1.75 -0.96 -1.05 -1.32 -1.14 -1.23 -0.97 -1.59 -1.61 -1.00 -1.26 -0.84 -0.91 -1.24 -1.28 -1.47 -0.95 -1.37 -2.02 -2.02 Ha (7) [OUI] 6716 -1.16 -1.25 0.75 0.38 0.28 0.62 (8) (9) 0.79: 0.81: 0.98 2.2. SpectralClassification 0.98 0.74 0.74 0.74 0.74 0.78 0.93 0.71 0.71 0.79 0.74 0.74 0.93 0.93 0.68 1.05 1.00 0.93 0.66 1.02 1.00 1.10 1.00 1.10 1.02 N 620: L (10) (11)(12)(13)(14) e 690 H 510 H 450 S2 430 SI 590 H 160 S2 790 S2 100 H 190 S2 80 H 90 L 40 L a H [Nil] [Sil][OI]Adopt L HH: Spectral Types 179 19 95ApJS. . .98. .171V MCG+03-10-045 Name IR 12450+3401 IR 11571+3004 IR 09433+1910 IR 09427+1929 IR 09425+1751 Zw 182.010 IR 09399+2830 IR 09339+2835 IR 09338+3133 IR 09303+2736 IR 09268+2808 IR 09209+3943 IR 07599+6508 *NGC 985 *Zw 041.073 *IR 12071-0444 *IR 10210+7528 Zw 238.066 IR 09252+3124 IR 09245+3300 IR 09245+3517 IR 09218+3428 *IR 04259-0440 *IR 02433+1544 (i) Observed andDereddenedLineRatios,Densities,SpectralClassification—WarmIRASGalaxies © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.24; 4.37: 15.9: 7.94; Ha 13.5: H/3 — E(B-V) 6.92 3.10 3.10 3.10 3.10 2.85 3.10 9.33 3.10 6.17 3.10 3.10 8.71 3.10 2.85 2.85 5.37 2.85 5.89 2.85 7.94 2.85 2.85 7.08 5.62 2.85 2.85 2.85 2.85 2.85 7.24 2.85 15.9 1.00 14.4 7.94 2.85 7.59 2.85 1.00 15.5 1.00 11.2 1.00 (2) 0.05; 0.43: 0.95; 1.72: 1.47: 0.64 0.89 0.63 0.95 0.91 0.69 0.99 0.78 0.93 1.02 1.12 1.55 1.73 1.10 1.62 1.36 (3) -0.39: -0.37: -0.53: -0.45: [OUI] [Nil][Siq[OI][Oil]6731 -0.58 -0.64 -0.79 -0.63 -0.01 -0.59 -0.34 -0.30 -0.76 -0.14 -0.08 -0.21 -0.48 -0.23 -0.19 -0.70 -0.62 -0.04 -0.63 -0.59 -0.18 -0.53 0.22; 0.07: 0.07: 0.27; H/j H[OUI]6716[Nil][SU][OI]Adopt 0.23 a 0.70 0.77 0.18 0.20 0.26 0.20 0.09 0.27 1.09 1.05 (4) (5)(6)(7)(8)<9)(10)(11)(12)(13)(14) -0.40 -0.69 -0.40 -0.66 -0.51 -0.51 -0.34 -0.25 -0.25 -0.30 -0.33 -0.32 -0.35 -0.38 -0.38 -0.37 -0.49 -0.51 -0.21 -0.20 -0.34 -0.41 -0.30 -0.36 -0.36 -0.09 -0.09 -0.35 -0.26 -0.61 -0.25 -0.36 -0.34 -0.14 -0.29 -0.13 -0.26 -0.50 -0.54 -0.22 -0.76 -0.21 -0.71 -0.41 -0.35 -0.23 -0.22 -0.37 -0.35 0.10; 0.10; 0.31: 0.23:-0.83: 0.63 TABLE IB 180 -0.28 -0.23 -0.67 -0.48 -0.63 -0.61 -0.62 -0.61 -0.56 -0.63 -0.67 -0.65 -0.47 -0.65 -0.50 -0.46 -0.58 -0.56 -0.63 -0.46 -0.57 -0.53 -0.59 -0.41 -0.43 -0.40 -0.64 -0.61 -0.49 -0.44 -0.56 0.21; 0.21; 0.05 -0.41; -0.41; -1.27: -1.51: -1.55: -0.34: -1.55: -1.57: -1.60: -1.34: -1.59: -1.68: -1.68: -1.84 -1.78 -1.08 -1.16 -1.00 -1.53 -0.86 -1.03 -1.60 -1.66 -1.17 -1.42 -1.61 -1.53 -1.57 -1.48 -0.91 -1.58 -1.62 -1.22 -1.38 -1.57 -1.13 -1.18 -1.42 -1.47 -1.05 -1.13 -0.05: -0.73 -0.59 -0.46 0.88: 0.45 0.63 0.23: 0.42: 0.59 2.14; 0.49 0.07 0.37 0.75 0.37 0.88 0.58 0.00 0.65 0.92 0.55 0.57 2.14 0.11 0.58 0.32 0.67 1.17 0.79 0.81 0.72 0.74 0.74 0.74 0.59 0.81 0.78 0.72 0.72 0.72 0.74 0.79 0.78 0.72 0.87 0.87 0.91 0.91 0.72 >2000 N. 200 310 390 100 180 140 90 H 60 60 50 S2 SI S2 H H H H H H H H L H H H H H L L L L H Spectral Types 51 S2 52 H: L: H H H H H H H H H H H H H L L L 19 95ApJS. . .98. .171V IR 15206+3342 IR 14341+3017 *IR 15304+3017 IR 14416+6618 IR 14229+1425 Name *IR 15463+4131 *IR 15445+3312 *IR 15418+3938 *IR 15414+3238 *IR 15404+3228 *IR 15394+3532 ’“IR 15312+4236 *IR 13446+1121 IR 13349+2438 *IR 15440+2834 *IR 15418+2840 *IR 15391+3214 *IR 15384+3841 ’•'IR 15359+3139 *IR 15358+3831 *IR 15324+3203 *Zw 102.056 *IR 15364+3320 a) American Astronomical Society •Provided bythe NASA Astrophysics Data System NW SW NE SE Ha H/J 6.03 6.61 3.10 4.57 3.10 8.51 4.90 3.10 4.07 8.32 3.98 3.10 2.85 12.3 2.85 2.85 3.10 2.85 2.85 7.24 15.9 2.85 2.85 2.85 7.24 2.85 2.85 2.85 5.50 3.10 3.10 2.85 7.08 2.85 5.25 2.85 5.37 3.10 6.31 10.0 1.00 10.7 5.62 2.85 7.76 5.50 14.1 2.85 1.00 1.00 (2) E(B-V) 0.67 0.84 0.38 0.94 0.36 0.54 0.95 0.33 0.91 0.57 1.47 1.64 0.61 0.64 0.92 1.09 1.08 0.67 0.56 0.81 1.27 1.34 1.52 (3) [OUI] [Nil][SII] -0.10 -0.25 -0.64 -0.27 -0.25 -0.88 -0.83 -0.67 -0.64 -0.07 -0.29 -0.57 -0.24 -0.19 -0.65 -0.60 -0.39 -0.35 -0.50 -0.34 -0.48 -0.27 -0.36 -0.09 -0.05 -0.58 -0.30 -0.61 % HaH« 0.97 0.99 0.11 0.19 0.42 0.45 0.28 0.31 0.02 0.06 0.80 0.83 0.69 0.62 0.07 1.14 1.17 0.11 (4) (5)(6) TABLE IB—Continued -0.06: -0.06: -0.24 -0.51 -0.50 -0.51 -0.50 -0.10 -0.09 -0.43 -0.42 -0.25 -0.37 -0.37 -0.25 -0.23 -0.39 -0.38 -0.31 -0.31 -0.46 -0.47 -0.43 -0.22 -0.01 -0.43 -0.22 -0.09 -0.35 -0.35 -0.01 -0.50 -0.30 -0.28 -0.32 -0.31 -0.66 -0.66 -0.50 -0.31 -0.16 -0.28 -0.49 -0.49 -0.40 -0.16 -0.40 -0.28 -0.25 -0.49 -0.41 -0.40 -0.54 -0.49 -0.69 -0.64 -0.62 -0.64 -0.62 -0.51 -0.61 -0.65 -0.68 -0.64 -0.61 -0.92 -0.32 -0.95 -0.65 -0.64 -0.61 -0.57 -0.32 -0.76 -0.74 -0.62 -0.58 -0.56 -0.52 -0.45 -0.43 -0.33 -0.60 -0.30 -0.27 -0.26 -0.24 -0.60 -0.76 -0.71 -0.69 -0.66 181 -1.62: -1.60: -1.05 -1.19 -1.64 -1.69: -1.26 -0.93 -0.63 -0.66 -1.47 -1.51 -0.95 -1.62 -1.70 -1.35 -1.40 -1.66 -1.44 -1.47 -1.03 -1.11 -1.68 -1.35 -1.41 -0.86 -1.56 -1.61 -1.35 -1.51 -1.55 -1.41 -0.83 -1.41 -1.44 -1.36 -1.64 -1.01 -1.39 -1.61 -1.07 -1.12 -1.04 -1.42 -1.70 -1.35 -1.74 [OI] [Oil]6731 H« [OUI]6716 (7) (8)(9) -0.96 -1.12 -1.23 -0.24 -0.99 -0.09 -0.07 -0.31 0.87: 0.47: 0.80: 0.40: 0.60: 0.48 0.69 0.30 0.75 1.14: 0.78 0.61 0.46 0.49 0.82 0.02 1.07 1.18 0.79 0.19 1.28 0.22 0.72: 0.72: 0.71 0.98 0.78 0.79 0.71 0.98 0.62 0.76 0.76 0.62 0.72 0.72 0.89 0.87 0.83 0.87 0.78 0.91 0.87 0.85 0.83 0.87 0.78 0.76 0.85 0.93 0.93 0.71 0.72 0.83 0.76 0.85 1.07 1.05 1.05 N. (10) (11)(12)(13)(14) 330 510 370 310 110 430 160 270 260 740 240 710 150 100 60: 30 60 50 [Nil] [siq[oqAdopt S2 S2 52 HS2 S2 51 SI H H H H H H H H H H H H H H L H H L L L H Spectral Types H H L S2: S2 S2 H: 52 51 L: L: H H H H H H H H H H H H H H H L 19 95ApJS. . .98. .171V *IR 21549-1206 *IR 21484-1314 *IR 21479-1305 IR 16130+2725 Zw 052.015 *IR 16007+3743 *IR 15597+3133 *IR 15589+4121 *IR 15577+3816 *IR 15569+2807 *IR 15549+4201 *IR 15545+4000 *IR 15543+3013 *IR 15543+4158 *IR 15535+2854 *IR 15534+3519 *IR 15534+3004 *IR 15483+4227 *IR 15519+3537 *IR 15514+3330 *IR 15481+2920 *IR 15469+2853 Name (i) American Astronomical Society •Provided bythe NASA Astrophysics Data System NW NW SE SE W E 5.62: 17.4: 3.10 H 4.07 4.68 3.10 2.85 % 2.85 3.10 13.2 2.85 7.94 2.85 3.10 1.00 5.89 3.10 3.16 10.5 3.10 1.00 9.55 4.57 2.85 4.90 1.00 2.85 2.85 3.31 2.85 2.85 2.85 5.25 8.32 3.63 3.10 6.61 3.10 0 2.85 2.85 2.85 4.47 6.61 3.10 7.24 2.85 2.85 2.85 1.00 10.5 (2) E(B-V) 0.59: 1.73: 0.36 0.41 0.74 1.54 0.02 1.03 1.21 0.48 0.55 0.16 0.61 1.14 0.94 0.25 0.85 0.44 0.76 1.08 1.31 (3) -0.05: -0.19 -0.13 -0.70: -0.65: -0.37 -0.32 -0.06 [oiiq [Nil][siq[oq[oiq6731 -0.16 -0.14 -0.10 -0.07 -0.17 -0.12 -0.29 -0.28 -0.19 -0.43 -0.41 -0.19 -0.12 -0.23 0.02: 1.01 1.04 0.12: 0.20: 0.00 0.11 0.02 0.13 0.06 0.10 H/? 0.00 0.50 0.50 0.11 0.13 1.07 0.30 0.31 0.31 0.35 (4) TABLE IB—Continued -0.45 -0.48 -0.48 -0.42 -0.66: -0.45 -0.41 -0.62: -0.14 -0.41 -0.40 -0.46 -0.29 -0.46 -0.29 -0.30 -0.20-0.55 -0.79 -0.40: -0.79 -0.40: -0.07 -0.07 -0.33 -0.16 -0.15 -0.33 -0.21 -0.21 -0.68 -0.68 -0.44 -0.43 -0.26 -0.32 -0.25 -0.33 -0.37 -0.37 -0.29 -0.36 -0.35 -0.44 -0.08 -0.07 -0.23 -0.22 -0.28 -0.43 0.04 H 0 (5) (6)(7)(8) -0.68: -0.66: -0.38: -0.36 -0.57 -0.60 -0.27: -0.54; -0.53; -0.48 -0.47 -0.38 -0.37 -0.13 -0.50 -0.47 -0.72 -0.70 -0.33 -0.31 -0.43 -0.55 -0.39 -0.53 -0.75 -0.74 -0.82 -0.79 -0.57 -0.56 -0.70 -0.66 -0.52 -0.78 -0.75 -0.55 -0.54 -0.48 182 -1.04: -1.66: -1.62: -0.90: -0.31: -0.90: -0.32: -0.96: -1.02: -1.62: -1.67: -0.79: -1.34 -1.36 -1.16 -1.18 -1.43 -1.51 -1.66 -1.71 -1.07 -1.14 -0.81 -0.84 -1.41 -1.44 -1.56 -1.59 -1.60 -1.61 -1.24 -1.27 -1.21 -1.02 -1.03 -1.16 -1.14 -1.50 -1.57 -1.26 -1.08 -1.46 -1.59 -1.30 H [OUI] a -0.87 -0.05 0.27: 0.12: 0.17: 0.07: 0.50 1.02 0.49 0.29 0.02 0.47 0.21 0.22 1.41 1.17 0.61 0.92 0.36 0.95: 0.95: 0.72: 0.74: 6716 0.78 0.78 0.76 0.76 0.79 0.79 1.07 0.87 0.85 0.87 0.68 0.69 0.87 0.89 0.76 0.76 0.74 0.74 0.85 0.65 0.66 0.85 0.76 0.76 (9) 480: N (10) (11)(12)(13)(14) e 150 H 120 HL 740 170 310 330 290 S2 110 280 130 70: 90 a LH [Nil] [SII][OI]Adopt H H H H ...L H S2S2: H H H L H L H H L H H L H L H L H L H Spectral Types S2 H: H: H: L: H: H: L: L: H H L: L: H H H H H H H 19 95ApJS. . .98. .171V See §2.2forfurtherdetail. (:) indicatesgalaxieswithlineratios thatdonotcorrespondtothesamespectraltypeinallthreediagrams ofVeilleux&Osterbrock1987. H =iigalaxies.LLINER(“low-ionization nuclearemission-lineregions”),S2=Seyfert2galaxies, and SI=Seyfert1galaxies.Acolon ± 25%.(a)Unreasonablephysicalinput(lowdensitylimit):6716/6731 >1.45.(*)Objectobservedunderphotometricconditions. [col. (11)],[Sil]XX6716,6731(12)],and[Oi]X6300(13)]. Column (14)liststheadoptedspectraltype.Meaningsofsymbols: IR 22472+3439 *IR 22381-1337 *IR 22343-0840 *IR 22338-1015 *IR 22283-1439 *IR 22279-1112 *IR 22225-0645 *IR 22220-0825 IR 22199-0345 *IR 22213-0238 *IR 22204-0214 *IR 22193-1217 *IR 22191-1400 *IR 22152-0227 *IR 22114-1109 Name -3 Column (11)through(14)—Opticalspectraltypesdeterminedfromthe diagramsofVeilleux&Osterbrock1987involving[Nil]X6583 Column (10)—Electrondensityincmderivedfromthe[Sn]fluxratio. Column (9)—[Sn]X6731/[SX6716. Column (8)—Logarithmofreddening-corrected[On]X3727/[0in]X5007. Column (6)—Logarithmofreddening-corrected[Sn]XX6716,6731/Ha. Column (4)—Logarithmofreddening-corrected[Om]X5007/H/3. Column (2)—Ha/H/3. Column (7)—Logarithmofreddening-corrected[Oi]X6300/Ha. Column (5)—Logarithmofreddening-corrected[Nn]X6583/Ha. Column (3)—Colorexcessesdeterminedfromtheemission-lineBalmer decrements(see§2.1). Column (1)—Targetname. Notes.—The uncertaintyontheemissionlineratiosistypically±10%. Forentrieswithacolon(:)theuncertaintyisapproximately a) © American Astronomical Society • Provided by theNASA Astrophysics Data System NW NW SE SE 14.8: 11.6: H« H/J 3.10 3.10 2.85 8.91 3.10 6.46 5.50 5.01 2.85 1.00 2.85 8.71 15.9 2.85 2.85 2.85 6.61 3.10 7.59 2.85 3.10 6.17 9.33 3.10 2.85 7.24 2.85 7.76 5.50 2.85 10.5 2.85 (2) E(B-V) 1.57: 1.41: 0.66 0.57 0.82 0.98 0.95 1.14 0.69 0.85 0.58 1.72 0.92 1.11 1.30 1.19 (3) -0.47: -0.39 -0.54: -0.47: [OUI] [Nil][SII][OI][Oil]6731 -0.07 -0.01 -0.37 -0.32 -0.58 -0.53 -0.05 -0.02 -0.61 -0.57 -0.05 -0.59 -0.55 -0.12 -0.58 -0.52 0.23 0.31 Hß 0.24 0.27 0.23 0.27 0.86 0.90 0.58 0.62 0.59 0.62 (4) TABLE IB—Continued -0.39 -0.61 -0.61 -0.23 -0.23 -0.39 -0.12 -0.17 -0.16 -0.10 -0.09 -0.55 -0.56 -0.27 -0.27 -0.34 -0.36 -0.20 -0.20 -0.35 -0.36 -0.33 -0.27 -0.27 -0.21 -0.34 -0.28 -0.18 -0.17 -0.21 -0.21 -0.28 -0.21 H (5) a -0.86 -0.83 -0.55 -0.51: -0.38 -0.36 -0.71 -0.70 -0.48 -0.56 -0.53 -0.55 -0.50 -0.27 -0.22 -0.66 -0.68 -0.64 -0.50 -0.53 -0.56 -0.61 -0.60 -0.55 -0.78 -0.75 -0.68 -0.44 -0.42 -0.53 -0.65 -0.35 -0.32 183 H (6) a -0.75: -0.38: -0.46: -1.22 -1.61 -1.25 -1.64 -1.48 -1.54 -1.19 -1.28 -1.12 -1.16 -1.31 -1.37 -1.50 -1.34 -1.39 -1.42 -1.15 -1.22 -1.34 -1.38 -1.24 -1.17 -1.20 -1.30 -0.85 -0.90 -1.11 -1.08 Ha (7) [OIII] 6716 -0.02 -0.26 -0.32 -0.29 -0.65 -0.61 -0.68 -0.40 0.57: 0.16: 0.44 0.09 0.95 0.55 0.47 1.02 (8) (9) 1.10: 0.71 0.72 0.76 0.76 0.74 0.76 0.81 0.81 1.41 1.41 0.83 0.83 0.76 0.76 0.83 0.83 0.95 1.32 0.95 1.32 1.00 1.00 1950 1510 790: N (10) (11)(12)(13)(14) e 110 220 110 480 S2 230 LH 570 S2 240 H 120 H 50 ... HL ... H [Nil] [SII][OI]Adopt S2 H H H H L L L Spectral Types H H H H L L H: H: H: H: S2 S2 S2 H: L: H H H H H H L 19 95ApJS. . .98. .171V hereafter H80)definedtheclassofLINERs(“low-ionization tiating betweenthevariousionizationmechanisms.Allof correlation foranytypesofgalaxies. widths ofMgib.ThestarsaretheHngalaxies,opencircles after BPT81)andVeilleux&Osterbrock(1987,hereafter line ratiosusedbyBaldwin,Phillips,&Terlevich(1981,here- LINERs, andthefilledcirclesareSeyfertgalaxies.Thereisnoobvious D foreachspectraltype.Themeaning ofthesymbolsissameasinFig. V087 )wereincludedinouranalysis.Theseare[OHi]X5007/ many ofthediagnostictoolsknowntobeefficientatdifferen- underlying stellarabsorption(seePaperI).Heckman(1980, ratios involvingaBalmerlineusetheintensitycorrectedfor XX6716, 6731/Ha,and[Oi]X6300/Ha.Notethattheline 3. Acorrelationisobserved. 184 Hß, [OII]\3727/[0ni]X5007,[Nil]X6583/Ha,[Sn] Fig. 4.—Colorexcessesasafunction oftheequivalentwidthsNai Fig. 3.—EquivalentwidthsofNaiDasafunctiontheequivalent © American Astronomical Society • Provided by theNASA Astrophysics Data System VEILLEUX ETAL. 1 =-1 tion ofthedatapointsin diagramsof[Om]X5007/Hß ting gasinLIGswillbediscussed§3.Table1liststhevarious (13) listeachofthespectral types determinedfromtheloca- and V087.Theuncertaintyin thesedataistypically10%,and lines ratiosusedintheclassification schemeofH80,BPT81, grams. Thespatialvariationsofthepropertiesline-emit- parameterized byMiller&Mathews(1972;seeprevious ture-related effects,themoredistantLIGs(cz>20000 km section ). thus measuredandcomparedwiththediagramsinOTV92.All 25% fortheentrieswithacolon (:).Columns11),12and s" ;extractionwindowof4kpc)werenotplottedinthese dia- where theroleofgalaxyinteractioninLIGsisassessed. All from theHa/HßratioandWhitfordreddeningcurveas rected forreddeningusingthevaluesofE(B—V)determined Figures 6and7showthelocationsofLIGswithoutobvious of thelineratiosusedinpresentanalysishavebeencor- of [On]XX7320,7330/Haand[Sm]XX9069,9531/Hawere the symbolsaresameasinFig.3.Acorrelationisobserved. continuum levelnearHatotheHß.Themeaningof 2 kpc(i/o75kmsMpcandqo=0.5).Toavoidaper- nuclear valuesobtainedbyextractingthefluxfromcentral of themeasurementsinthesetablesandfiguresrepresent the of theobjectswithdoublenucleiispostponeduntil§2.10, companions inthevariousdiagnosticdiagrams.Ourdiscussion & Veilleux1992,hereafterOTV92).Whenpossible,thevalues wavelengths hasbeenexploredandfoundtohelpindetermin- & Wilson1985b;MorrisWard1988;KirhakosPhillips sion-line galaxies(Diaz,Pagel,&Terlevich1985a;Diaz, ing thedominantionizationprocessinopticallyselectedemis- for eachspectraltype.Thecontinuumcolorisdefinedastheratioof cently, theuseoffineratiosinvolvingemissionlinesatlonger ratio wasthereforealsoincludedinouranalysis.Morere- nuclear emission-lineregions”)ashaving[Oil]X3727/m X5007 >1and[OI]X6300/[0m]|.Thislastline 1989; Osterbrock,Shaw,&Veilleux1990;Tran, The resultsofouranalysisaresummarizedinTables1and 2. Fig .5.—Colorexcessesasafunctionoftheobservedcontinuumcolors C6563/C4861 Vol. 98 19 95ApJS. . .98. .171V reanalyzed usingourmoreaccurate treatmentoftheunderly- This trendwasfirstobserved intherelativelysmallsampleof Sanders etal.(1988a).Allof theobjectsintheirsamplewere four Seyfert1galaxiesinour samplehavelog(L/Lo)>12. galaxies (12%),and48LINERs(27%).Finally,thespectral and fortheseobjectstobemore Seyfert-like.Infact,threeofthe dency forthemoreluminousobjectstohaveAGNlineratios termined duetoalackofdiagnosticemissionlines. types of18galaxies(9%thetotalsample)couldnotbe de- on theinfraredluminosity.Perhapssinglemostimportant by hotstars(Hngalaxies).AGNemissionlineswereobserved result listedinTable3andshownFigure8istheclear ten- in 74nuclei(41%)includingfourSeyfert1galaxies(2%,Mrk 231, IR0759+65,1334+24,andNGC7469),22Seyfert 2 ( 108galaxies)havespectracharacteristicofphotoionization nosity discussedbelow. estimates thefractionofAGNsamonglowerluminosity double-nucleus systemsisconservativeinthesensethatitover- objects andthuscannotexplainthetrendswithinfraredlumi- interacting systemsaremorecommonbelowlog(L/L)= two nuclei:galaxypairswithspectraltypesHn-LINER,HII- and Seyfert1-Seyfert2wereclassifiedasLINER,2, we adoptedinTable3themoreSeyfert-likespectraltypeof Seyfert 1,2,andrespectively.These Seyfert 2,Hn-Seyfert1,LINER-Seyfert are systemsmadeupoftwodistinctnuclei.Forthesesystems, than 75%ofthegalaxiesinsamplehavelineratioscorre- given inTable3andgraphicalformFigure8.Theclassi- V087. Outofthe200LIGsinsample,32themclearly sponding tothesamespectraltypeinallthreediagramsof fication schemewasfoundtoberelativelyunambiguous:more two methodsofclassificationgiveconsistentresults(col.[11]). tion basedontheseredderlinesismoreuncertainthanthe based onthepreviousfourcolumns.Acolon(:)nextto ir positions inthediagramsofOTV92.Notethatclassifica- fewer objects(seeOTV92).Nevertheless,wefindthatthese spectral typesdeterminedinTable1becauseitisbasedon and (10)givethespectraltypesofeachobjectbasedontheir uous inthesensethatlineratiostheseobjectsdonot adopted spectraltypeindicatesthattheclassificationisambig- teria ofH80.WeadoptedthisdefinitionLINERsbecause galaxies whileinthesecondgroupwerecalledLINERs V087. Table2liststhe11objectsforwhich[Oil]X7325or correspond tothesamespectraltypeinallthreediagramsof nally, column(14)ofTable1givestheadoptedspectraltype measurements of[Oil]X3727wereoftennotavailable.Fi- although afewofthemdonotsatisfytheoriginalLINERcri- excitation. Thefirstgrouprepresentsthe“classic”Seyfert2 No. 1,1995 12 (§2.10).Consequently,thisclassificationmethodofthe high ([OHi]X5007/>3)andlowmHß< [S m]XX9069,9531couldbemeasured.Columns(8),(9), ir0 were determinedfromanoptically-selectedsampleofgalaxies A distinctionwasmadeamongAGNsbetweentheobjectsof and basedonthepublishedresultsofphotoionizationmodels. classify eachobjectasHngalaxiesorAGNs.Theseboundaries versus [Nn]X6583/H«,[Sil]XX6716,6731/Ha,and[Oi] X6300/Ha, respectively.WeusedtheboundariesofV087to Table 3alsoshowsthedependenceofLIGspopulation We foundthat59%oftheclassifiedobjectsinsample A summaryoftheresultsfromspectralclassificationis © American Astronomical Society • Provided by theNASA Astrophysics Data System LUMINOUS INFRAREDGALAXIES.II. detectable WRfeatures(e.g., combinationsofHeilX4686, ple islocatedintheESBregion definedbyAllenetal.orhave to thegalaxiesstudiedbyFrench (1980).Noobjectinoursam- gram representgalaxieswithaveryrecentburstofstarforma- 4642). He iX5876,CmX5696,Niv X5737,NmXX4634,4640,and tion (“extremestarburstgalaxies”orESB).Theseobjectshave emission-line andcontinuumpropertieswhichareverysimilar the high-[0m]/Hßandlow-[Nn]/Haregionoftheir dia- was alsofoundinthesamplesofLeechetal.(1989),AHM89, Allen etal.havearguedthatthedozenofobjectspopulating Allen etal.(1991),andAshby,Houck,&Hacking1992). This generallackofhigh-ionizationHIIgalaxiesamongLIGs this regionofthediagramsispopulatedwithextranuclearHn Dopita 1985;McCall,Rybski,&ShieldsFrench1980). account forthehighionizationleveloftheseobjects(Evans & ygen-depleted environment[(O/H)=0.1-0.75(O/H)©] can the factthatessentiallyallofobjectsclassifiedasHngalax- stars withhigh-ionizationparameterand/orlocatedinan ox- of French(1980).Photoionizationbyhot(T*^40000K) regions andthelow-luminosityHngalaxiesfromsample ies haverelativelylowionizationlevel([Om]X5007/Hß< region ofthesediagramsisdevoidanydatapoints,reflecting variations ofthelineratiosarediscussed. parent discrepancywillbeaddressedin§3.2wherethespatial presented. the lineandcontinuumemissionoftheseobjectshavebeen 3). ThisistobecontrastedwithFigures1-3ofV087where postponed until§4.1.1,onceallofthequantitiesderivedfrom Our discussionoftheprocessesrelevanttoLINERLIGsis debate inthepastdecade(seeFilippenko1989forareview). minosity intheirmoredistantsample.Theoriginofthisap- Leech etal.(1989)whofoundnodependenceoninfraredlu- Allen etal.(1991),butseemtodisagreewiththeresultsof ization processinLINERshasbeenthesubjectofconsiderable LIG population,regardlessoftheinfraredluminosity.Theion- log (L)>12.Theseresultsareconsistentwiththestudyof grams. Fortunately,suchshiftsdonotgenerallyaffectthespec- are genuineSeyfertgalaxiesisonlyabout54%evenwhen AGNs. WefindthatthefractionofAGNsinoursamplewhich does changetheproportionofSeyfert2’stoLINERsamong galaxies andnarrow-lineAGNisnearlyvertical.However,it tral classificationoftheobjectsasboundarybetweenHn scopic studiesofLIGshasresultedinsignificantuncertainties grams ofV087.Webelievethattheinaccuratetreatment in theverticalpositionsofdatapointsdiagnosticdia- shift ofthedatapointstowardhigh[Oin]/Hßinallthreedia- underlying stellarcontinuuminmanyoftheearlierspectro- Balmer absorptionlinesthereforeproduceanearlyvertical the BalmerabsorptionlineshavealargereffectsatHßthan in absorption.Underestimatesoftheequivalentwidth al. Indeed,errorsintheestimatesofequivalentwidths equivalent widthsoftheBalmerabsorptionlinesbySanderset difference isentirelyattributabletounderestimatesofthe than thepublishedvaluesofSandersetal.(1988a).The Ha becausetheBalmerdecrementissteeperinemissionthan ir ing Balmerabsorptionlines(seePaperI).Ourmeasured [O hi]X5007/Hßratioswerefoundtobeconsistentlysmaller A quickinspectionofFigure6indicatesthattheupperleft Finally, Table3showsthatLINERscontribute—27%ofthe 185 > r-\—I 186 VEILLEUX ET AL. Vol. 98
log([SII]6716+6731/Ha)
log([0I]6300/Ha) Fig. 6a Fig . 6.—Dereddened flux ratios as a function of infrared luminosities for single nucleus systems in {a) the BGSs sample and ( Z>) the WGSs sample. The open squares represent galaxies with log (1^/LQ) < 11, the squares with an “X” in the middle are galaxies with 11 < log (L^/Lo) < 12, and filled squares are galaxies with log (L^/Lo) > 12. H il galaxies (H) are located to the left of the solid curve while AGN are located to the right of that curve. AGNs were further classified as Seyferts or LINERs depending on whether or not [O ill] A5OO7/H0 > 3 (indicated by a solid horizontal segment).
2.3. Luminosities and Equivalent Widths of Ha median of the Ha luminosities (equivalent widths) for Seyfert, LINER and H n LIGs are 7.8 X 1041 ergs s-1 (63 Â), 3.5 X The reddening-corrected Ha luminosities of our sample gal- 1041 ergs s"1 (29 Á), and 9.5 X 1041 ergs s-1 (55 Á), respec- axies are listed in Table 4. These luminosities were derived tively. The small equivalent widths in LINER LIGs perhaps from the nuclear spectra ( see Paper I ). Only data taken under indicate that the stellar continuum in LINERs is less reddened photometric conditions were included in the final analysis. Fig- than the line emission. This possibility could also explain the ures 9 and 10 show the distributions of LHa and EW(Ha) as a fact that only a weak correlation was found in § 2.1 between function of spectral types. LINER LIGs appear to be deficient the continuum colors of LINER LIGs and E(B - V) deter- in Ha emission relative to both Seyfert LIGs and H n LIGs: the mined from their emission-line Balmer decrements.
© American Astronomical Society • Provided by the NASA Astrophysics Data System > r-\—I \—I No. 1, 1995 LUMINOUS INFRARED GALAXIES. II. 187 00 Helou 1987). A similar result was found by Leech et al. ( 1989). This “deficit” of Ha emission may be due to an un- ^0 derestimate of the dust extinction or to fundamental differ- a LO ences in the production mechanisms of the Ha and infrared emission in these two types of objects. Slit losses may account for the large ratios in the nearby objects (Leech et al. 1989). We also observe in our sample of objects a weak tendency for Lit/LHa to increase with infrared luminosity. As found by AHM89, the median log EW(Ha) of our H II LIGs ( ~ 1.7 ) is closer to the values of the nuclear H n regions ( —1.5; Kennicutt et al. 1989) than the values of disk H n re- gions (^2.7; Kennicutt et al. 1989). This low value of EW(Ha) in the H ii galaxies of our sample can be explained if the time since the burst of star formation in these objects is of order ~107 yr (using Fig. 1 of DeGioia-Eastwood 1985 and the continuum colors of Jacoby, Hunter, & Christian 1984) or if an underlying old preexisting population is also contributing to the continuum light. This question will be addressed in more log([0II]3727/[0IIl]5007) detail in §§ 2.7 and 2.8 where the absorption features and the color of the continuum in these objects are discussed. 2.4. Densities An estimate of the density of the line-emitting gas in lumi- nous infrared galaxies may be derived from reddening-cor- rected line ratios. The density-sensitive lines [On] XX3726, 3729 could not be resolved in these galaxieso because of their large intrinsic velocity widths and the 8-10 Á spectral resolu- tion of the observations. The density was instead derived using the [S il] X6731/X6716 line ratio and the five-level-atom cal- culations of De Robertis, Dufour, & Hunt (1987). Columns (9) and ( 10) of Table 1 list the values of this ratio and their corresponding densities for all of the galaxies in the sample. The flux of the individual [ SII ] lines was determined by fitting simultaneously two Gaussian profiles to the blend (see Paper I ). Figure 12 shows the distribution of the density values for all of the LIGs of our sample as a function of their spectral type. The mean, median, and standard deviation around the mean of the density in the BGSs LIGs are 320, 250, and 260 cm-3, -1 0 1 log([0II]3727/[0IIl]5007) respectively. The average density in Seyfert 2 galaxies (430 cm-3) is somewhat larger than in H n galaxies (280 cm-3), Fig. 7.—Dereddened flux ratios involving [O n] \3727/[0 m] X5007. while LINERs have intermediate values (350 cm-3). The av- Meaning of the symbols are the same as in Fig. 6. erage [S ii] density in the AGN LIGs is considerably smaller than the average [S ii] density found by Koski ( 1978) in his sample of 30 Seyfert 2 and narrow-line radio galaxies {ne ^ The Ha luminosities of the HII LIGs of our sample are con- 2000 cm-3) but is comparable to the value found by Keel siderably larger than those found by Kennicutt et al. ( 1989) in ( 1983) in his sample of LINERs (^ ^ 450 cm-3). It is impor- their sample of nuclear H n regions and bright disk H n regions tant to point out that the low ionization potential and critical 39 -1 (LHa ^ 3 X 10 ergs s for the objects with log [N n]/ density of these two [S n] lines (see Osterbrock 1989) implies Ha <-0.15), and they are somewhat brighter than the star- that the densities derived from this line ratio are typical of re- 40 -1 burst galaxies of Balzano ( 1983; LHa ~ 5 X 10 ergs s ). On gions of low ionization and density. In Seyfert galaxies and the other hand, the infrared-selected Seyfert 2 galaxies have LINERs, densities derived from lines of higher ionization po- Ha luminosities which are comparable to those of optically tential and critical density are often larger than the [S ii] den- 42 -1 selected Seyfert 2 galaxies (LUa ^ 1 X 10 ergs s for an aver- sity due to stratification effects (e.g., De Robertis & Osterbrock age color excess of 0.54; Dahari & De Robertis 1988). 1986, and references therein). A possible explanation to the A strong (P[null] = 10~9) correlation between reddening- apparent difference between the [S n] densities of AGN LIGs corrected Ha luminosities and infrared luminosities is ob- and optically selected AGNs is that the extinction due to dust served among the H n LIGs but is much weaker in AGN LIGs is more important in LIGs than in optically selected AGNs, (P[null] ^ 0.01; Fig. 11). The H n LIGs in our sample have preventing us to probe the inner, denser [S n] line-emitting Lit/LHa - 300-3000, significantly larger than the ratios typi- zone in the LIG. A discussion of the density variations as a cally observed in the disks of bright spiral galaxies (Persson & function of distance from the nucleus is postponed until § 3.3.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 19 95ApJS. . .98. .171V Veilleux &Osterbrock(1987).See§2.2forfurtherdetail. colon (:)indicatesgalaxieswithlineratiosthatdonotcorrespondtothesamespectraltypeinallthreediagramsof respectively. Column(11)liststheadoptedspectraltypefromTable1.Meaningsofsymbols:H=HIIgalaxies, L =LINER(“low-ionizationnuclearemission-hneregions”),S2Seyfert2galaxies,andS11galaxies.A is approximately±25%.(*)Objectobservedunderphotometricconditions,(u)Upperlimit. *IR 15304+3017 WGSs Objects *1R 10210+7528 *NGC 7714 *NGC 7674 *NGC 5256NE MCG-02-33-098 IR 08339+6517 BGSs Objects *NGC 5256SW NGC 1614 *UGC 8335SE IR 03359+1523 Name Columns (8)through(11)—OpticalspectraltypesdeterminedfromFigs.6,7,and4ofOsterbrocketal.1992, Column (7)—Logarithmofreddening-corrected[Sm]AA9069,9531/Ha. Column (5)—Logarithmofreddening-corrected[Sn]AX6716,6731/Ha. Column (6)—Logarithmofreddening-corrected[On]A7325/Ha. Column (4)—Logarithmofreddening-corrected[Om]A5007/Hß. Column (2)—Ha/Hß. Column (3)—Colorexcessdeterminedfromtheemission-lineBalmerdecrements(see§2.1). Column (1)—Targetname. Notes.—The uncertaintyontheemissionlineratiosistypically±10%.Forentrieswithacolon(:) (1) Number ofobjects5412224 200 Classified 49(100%)112(100%)21(100%) 182(100%) Unclassified® 5103 18 a AGN 14(29%) 47(42%)13(62%)74(41%) HII 35(71%)65(58%)8(38%) 108(59%) Insufficientnumberofmeasuredemission linesforproperclassification. Observed andDereddenedRedLineRatios,Red-lineSpectralClassification © American Astronomical Society • Provided by theNASA Astrophysics Data System LINER 12(25%) 30(27%)6(29%)48(27%) Sey 22(4%) 16(14%)4(19%)22(12%) Sey 10(0%) 1(1%)3(14%)4(2%) W logtLJLo) <1111-12;>12 All 5.50 2.85 3.10 5.37 2.85 2.85 4.27 2.85 3.55 3.10 3.89 3.10 6.31 3.10 3.89 6.46 2.85 2.85 7.59 2.85 5.25 12.3 H H/3 (2) a E(B-V) 0.57 0.63 0.21 0.23 0.72 0.83 0.22 0.40 0.99 0.61 1.46 (3) -0.04 -0.01 [OUI] [SII] -0.01 -0.20 -0.13 -0.17 -0.12 0.18 0.19 0.62 0.65 0.14 0.16 0.03 0.22 0.24 0.06 0.03 1.14 1.17 1.06 1.07 H (4) ß Spectral Classifications -0.33 -0.32 -0.67 -0.65 -0.72 -0.71 -0.55 -0.41 -0.56 -0.44 -0.33 -0.33 -0.67 -0.65 -0.65 -0.62 -0.61 -0.72 -0.70 -0.61 -0.72 -0.69 Ha (5) TABLE 2 TABLE 3 -1.90u -1.82u -1.18 -1.11 -1.69 -1.66 -1.27 -1.24 -1.92 -2.01 -1.31 -1.28 -1.85 -1.74 -2.10 -2.05 -1.77 -1.90 [Oil] [Sill] Ha (6) -1.28 -0.81 -0.71 0.08 Ha (7) [OUI] (8) S2 S2 H H H/S2 H H H H L [SII] Spectral Types (9) S2 [SIII] Tab1 (10) (11) H/L S2 S2 S2 H: H H H H H H L 19 95ApJS. . .98. .171V -3 3- 6 with photoionizationeitherbystars(fortheLIGsclassified as temperatures derivedusingthefive-level-atomcalculations of models forphotoionizationbyhotstars,anactivenucleus, and cm. Typical[Oin]temperaturespredictedfromlow-density be determined(estimated)inthree(eight)H11galaxies,eight the objectsinsample.Similarly,[Om]X4363isgenerally ski, &Shields1985;FerlandNetzer1983;Binetteet al. collisional ionizationbyshocksare4000-14,000K,9000- De Robertisetal.(1987)anddensitiesof10cm 10 ERs. Table5liststhevaluesofthisratioalongwithelectron (10) Seyfert2galaxies,but,unfortunately,innoneoftheLIN- quite faintandisblendedwithH7complexabsorption H iigalaxies)orbyanactivenucleus(fortheSeyfert2LIGs). features. Overall,the[Oin]X5007/X4363temperaturecould ysis becauseoftheextremefaintness[Nil]X5755inall Unfortunately, thislastlineratiocouldnotbeusedinouranal- ments involve[Om]XX4363,5007and[Nil]XX5755,6583. optical lineratiosmostoftenusedintemperaturemeasure- mine thesourceofionizationline-emittinggas.Thetwo from carryingoutadetailedanalysis oftheemission-linepro- 1985). ThetemperatureslistedinTable5areallconsistent 18,000 K,and25,000-30,000respectively.(McCall,Ryb- with AGNemission-linespectraandthefractionofSeyfertsamongobjectsincreaseinfraredluminosity. The electrontemperatureisagooddiscriminanttodeter- The ratherlowspectralresolution ofourdatapreventsus Fig. 8.—Summaryoftheresultsspectralclassificationasafunctioninfraredluminosity.Bothfractionluminous galaxies © American Astronomical Society • Provided by theNASA Astrophysics Data System 2.5. ElectronTemperatures 2.6. LineWidths log(L/L)= 10-10.9911-11.99 ir0 Total =54 LUMINOUS INFRAREDGALAXIES.II. -1 1 ilar resultwasfoundinthesmaller sampleofAHM89.Line are drawnfromthesamedistribution is0.09(it0.07when H iigalaxiesshowsthattheprobability thatthesetwodatasets width distributions.AK-Stest onthelinewidthsofAGNand than themedianlinewidthofH11LIGs(320kmsversus only theLINERsarecompared withtheH11galaxies).Asim- 250 kms'),butwithconsiderableoverlapinthevarious line large linewidthstobeluminousintheinfrareddomain.Figure ple. AsshowninFigure13,thereisatendencyforobjectswith large spreadinlinewidthswasfoundtheobjectsofsam- trinsic andinstrumentprofilesareGaussiangivescor- emission linesorabsorptionfeatures(incontrasttoHa). A widths willbetreatedwithcaution. the quadraturemethodtocorrectobservedwidthsfor ments becauseitisstronginmostLIGsandfreeofanynearby and theconclusionsderivedfromouranalysisof line asymmetries willnotbeconsideredinthepresentdiscussion in AGNs;Whittle1985;Veilleux1991b).Forthisreason,line are morepeakythanGaussians(e.g.,theemission-lineprofiles rected widthsthataresystematicallytoohighforprofileswhich finite instrumentresolution.Thismethodassumesthatthein- tion onthemeasuredlinewidthsandasymmetriescanbe olution datacomefromtheuncertaintiesassociatedwithusing ancies betweenmeasurementsderivedfromlowandhighres- quite dramatic(e.g.,Whittle1985;Veilleux1991b).Discrep- axies haveshownthattheeffectsoffiniteinstrumentalresolu- files. Resultsfromhigh-resolutionstudiesofemission-linegal- 14 showsthatthemedianlinewidthofAGNLIGsislarger The [Oin]X5007linewasselectedforwidthmeasure- 12 -12.50 24 ■ Sey1 □ HII Sey 2 LINER Unclassified 189 r" \—i > ft
TABLE 4A Ha Luminosities—/iMS Bright Galaxies , 10 American Astronomical Society •Provided bythe NASA Astrophysics Data System Z S Ü O^ u o CN COY co Tt^ dddddddddd ÛpquqùùutqûÙPQ O CN• CN —voq-ONTt inOTtoor-N-voq-ONO cNCNcNcncncncNcNcncn TtinoooovoN-voinooN inoo —or'voooTtm vovor^oor^cno^tr~cn oooooooooo — CNd pppp —pTtpTfp Oven -—cnincncMoocN z S o ^ u Ü CO O § ON ' dddddddddd ÙÙÙpqÙPQÙÙÙÙ corteo —COCN—'VO^-CO — ooTfvo^tinr~-coTto cocococo^cococococo cor-oocN —vomm O'—'•«tCNinONOOCOCNvO vO^OOOcoONONOOrJ-r^ VOVOVOCOO^ONCOVOOV mincNco—-incNooo — oooooooooo d-P-PcNoddd^d dcNCNCNOodON^^^ in M' -^-Tj-TtN-COTtCOTtTtTt •ncNtqinpptqppp r'CNrfONCNcomcococN ° 2 o vo Ú &: 2 o, öööoöööödö ^vqcqov(S»nr~;co(N'^- wwwwwpqmwww fOTj-^-^cSf^TtcocJcn co-'^-com—cococococo r'V0Tj-~Lr)OO(N'— T+ coir)»noo
2 3 4 log^/LnJ Fig. 11.—Distribution of the ratios of the reddening-corrected Ha lu- minosities to the infrared luminosities for each spectral type. Note the larger scatter among Seyferts and (to a lesser extent) LINERs. those of H ii galaxies and LINERs, respectively. This result may imply that the stellar population in H n LIGs is younger than in the LINER nuclei. Note, however, that all of these equivalent widths are considerably smaller than the equivalent widths observed in nonactive spiral galaxies (EW[Mg \b] = 3.5-6.0 Á; Keel 1983; Stauffer 1982; Heckman, Balick, & Crane 1980; AHM89). Dilution of the old-star continuum by a power-law continuum produced by an AGN or the fea- tureless continuum of hot, young stars could explain this re- sult. In the case of a young starburst ( —107 yr), the small EW(Mg I b) can also be produced by red supergiants in the starburst itself without the need for an old preexisting stellar population ( see Bica et al. 1990 ). The equivalent width of the Ca n absorption triplet at XX8498, 8542, 8662 was also measured when possible. This feature is the strongest feature in the deep red spectrum of late- type stars and normal galaxies. Of the fourteen objects with spectral coverage extending up to these wavelengths, the equiv- alent widths of both Ca il X8542 and X8662 could only be mea- sured reliably in three objects. In the other objects, one of these lines was either not strong enough to be measured or the ob-
© American Astronomical Society • Provided by the NASA Astrophysics Data System 19 95ApJS. . .98. .171V high infraredluminosities. in Fig.3.Theobjectswithlarge[O m]A5007linewidthsgenerallyhave nosities foreachspectraltype.The meaningofthesymbolsissameas before drawinganystatisticallysignificantconclusionsabout place inatleasttheH11galaxiesZw041.073and102.056. (Ca ii)butsmallEW(Mg1b).Asimilareffectcanbetaking IR 22199-0345 red continuumlightoftheseobjectsandproducelargeEW IR 22152-0227 IR 22114-1109 IR 15418+2840 IR 15304+3017 IR 15206+3342 IR 14229+1425 IR 09425+1751 WGS Objects NGC 7674 NGC 7714 NGC 7592W NGC 5256NE NGC 1614 UGC 8335SE UI Zw35N IC 1623N BGS Objects 194 Fig. 13.—[Oin]A5007linewidths asafunctionoftheinfraredlumi- Ca iitripletdataonalargernumberofLIGswillbeneeded Name O) SE E © American Astronomical Society • Provided by theNASA Astrophysics Data System [OIII](A59 +A5007) 49 [O ni]A4363 Electron Temperatures 103 137 137 106 233 153 163 (2) 57 58 80 80 70 97 59 44 37 78 51 TABLE 5 log^/Lj 3 -3 N =10 e (cm) 12600 11580 16210 16210 12600 20860 14090 11580 14090 14900 12960 10950 16210 10950 14090 18650 17140 9790 (3) : (K) 6 -3 N =10 e (cm) 10070 7610 7200 9000 7200 7610 8760 8050 8050 7830 7000 6810 9520 9260 8510 8760 6440 8280 (4) VEILLEUX ETAL. Spectral Type (5) S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 H H H H H H H H Seyfert 2’s{allclasseshave[C6563/C4861] ^0.4).Assum- and AGNLIGsorbetweenLINER LIGsandinfrared-selected no significantcontinuumcolor differencesbetweenH11LIGs function ofspectraltypesispresented inFigure16.Thereare histogram showingthedereddenedcontinuumcolorsas a will usetheamountofdustderivedfromemission-line spectrum todereddenthecontinuumcolorsofourobjects. An lar continuumarereddenedbyexactlythesameamount, we the emission-lineBalmerdecrement(Fig.5).Although this result doesnotstrictlyimplythattheline-emittinggasand stel- C6563/C4861, correlatewiththereddeningdeterminedfrom of theLINERsand(toalesserextent)Seyfert2galaxies. type. TheaveragelinewidthofH11galaxiesissomewhatsmallerthanthat these objects(see§3.6). will providefurtherconstraintsonthestellarpopulationof the presenceofalargepopulationredsupergiantsinLIGs. 0 Our analysisofthespatialvariationsthesestellarfeatures In §2.1,wenotedthattheobservedcontinuumcolors, Fig. 14.—Distributionof[Oni]X5007linewidthsforeachspectral ^ 4 6 u 10 - 2 0 2004006008001000 I 1 2.8. ContinuumColors FWHM([0 III])kms" I HHh+ i—i—i—i—i—i—i—\—i—\—i—|- I Sey 2 LINER H II Vol. 98 19 95ApJS. . .98. .171V 9 tral type.LINERshavesignificantlylargerMgibequivalentwidthsthan H iigalaxies. No. 1,1995 effect isnotpresentwhenthe observedcontinuumcolorsare Ha equivalentwidthsalsohave smallC6563/C4861(butnot considered (Flnull]=0.57). Objectsinoursamplewithlarge creasing infraredluminosity(Pfnull]=0.01,Fig.\lb).This in thepresentstudy.However,thereisaweaktendency for flux levelat3800Ausedintheiranalysiswasnotmeasured relations cannotbedirectlyverifiedinoursamplebecause the bluer thanobjectsoflowerinfraredluminosity.Theyobserved a similareffectwhenconsideringtheequivalentwidthof the [C6563/C4861 ];Fig.18). [C6563 /C4861]amongtheBGSsobjectstodecreasewith in- Ha emissionlineinsteadoftheinfraredluminosity.These cor- have continuumcolors(uncorrectedforextinction)which are 0.54). AHM89arrivedatasimilarresultsfromtheirsmaller a stellarpopulationlessthan10yrold([C6563/C4861]^ sample. the stellarclustermodelsofJacobyetal.(1984),wefindthat derlying stellarpopulationandusingthecontinuumcolorsof most oftheobjectsinoursamplehavecolorscharacteristic ing thatmostoftheopticalcontinuumisproducedbyun- 0 0 0 Fig .15.—DistributionoftheequivalentwidthsMgibforeachspec- Leech etal.(1989)foundthatluminousgalaxiesgenerally © American Astronomical Society • Provided by theNASA Astrophysics Data System LUMINOUS INFRAREDGALAXIES.II. 7 tween thesevariousdistributions. C4861 ),foreachspectraltype.No significantdifferenceisobservedbe- the continuumcolorswithoutneedforanunderlyingold preexisting population. than ^10yr.Asdiscussedin§2.7andBicaetal.(1990), width andbluecontinuummatchestheirmodelinwhichthe such youngstarburstreproducestheweakMgIbfeatureand burst-to-galaxy massratiois~10%andtheburstageless respectively. ThecombinationofsuchsmallMgibequivalent (Mg Ib)measuredforthisclassofobjectsare0.39and1.11Á, (1990). Themedianvaluesof(C6563/C4861)andEW contribution canbeestimatedusingthemodelsofBicaetal. sistent withthisidea.InthecaseofHngalaxies,starburst ally smallMgIbequivalentwidthsinLIGs(see§2.7)iscon- is affecting(C6563/C4861)and/orEW(Mgi£).Theunusu- lack ofcorrelationcanbeunderstoodifastarburstoranAGN equivalent widths(Fig.19).Thisresultremainsthesamewhen dening-corrected continuumcolorsofLIGsandtheirMgIb H iiLIGsorAGNareconsideredindependently.This man etal.1980),nocorrelationwasfoundbetweenthered- 0 0 0 Fig. 16.—Distributionofdereddened continuumcolors,(C6563/ Contrary towhatisobservedinnormalgalaxies(e.g.,Heck- 195 > 196 VEILLEUX ET AL. Vol. 98 O'!00 h) a LO CO
log(Lir/LG) Fig. Ma Fig. 17.—Continuum colors as a function of the infrared luminosities, {a) observed colors, (b) dereddened colors. There is a weak tendency for the dereddened continuum to become bluer with increasing infrared luminosity.
2.9. Radio Fluxes contribute to the heating of the dust in these objects (the “in- frared cirrus” component). A strong correlation is known to exist between radio contin- The radio-infrared correlation is found to be considerably uum fluxes and mid-to-far infrared fluxes in the nuclei and weaker in optically selected Seyfert galaxies than in starburst disks of normal late-type galaxies as well as in the nuclei of galaxies (Condon & Broderick 1988). Quantitatively, if q is starburst galaxies (e.g., van der Kruit 1973; Helou, Soifer, & defined as the logarithmic FIR-radio flux-density ratio (see Rowan-Robinson 1985; Condon & Broderick 1986; Condon Condon et al. 1991), we have (#) = 2.34 for starburst galaxies & Broderick 1988; Wunderlich, Klein, & Wielebinski 1987; with very little scatter around the mean while radio-selected Condon, Anderson, & Helou 1991 ). The existence of this cor- active galaxies have q <2, suggesting an additional source of relation suggests that the radio and infrared continua have a radio emission in these objects. The values of q for the objects common origin in these objects. The infrared emission is prob- in our sample were calculated using the IRAS fluxes and the ably produced by warm dust heated by ultraviolet radiation 1.49 Ghz fluxes of Condon et al. ( 1990, 1991 ). The results of from massive {M ^ 8 A/©) stars. The radio emission, on the this analysis are presented in Figure 20. Although the scatter is other hand, is primarily nonthermal, synchrotron radiation as- considerable, Seyfert 2 galaxies have somewhat smaller values sociated with supernova explosions (and their remnants) from of q than H n galaxies and LINERs (2.17 vs. 2.37 and 2.42, the same population of massive stars, plus a smaller contribu- respectively). However, only four Seyfert 2 galaxies have q < tion of thermal emission from the H n regions produced by 2: NGC 1068, NGC 1143/44, NGC 5256NE (Mrk 266NE), these stars (Condon & Yin 1990). Thronson et al. (1990) and and NGC 7674. Condon et al. ( 1991 ) found a tendency in their Condon et al. ( 1991 ) suggested that lower mass stars may also sample for the scatter in q to increase with infrared luminosi-
© American Astronomical Society • Provided by the NASA Astrophysics Data System > ^ No. 1, 1995 LUMINOUS INFRARED GALAXIES. II. 197
Fig. \%a Fig. 18Z? Fig. 18.—Continuum colors as a function of the Ha equivalent widths in emission, (a) observed colors, (b) dereddened colors. H n objects with large Ha equivalent widths present blue observed continuum colors.
ties. A similar result is found in our slightly larger sample. Con- — V) determined from the emission-line Balmer decrements. don et al. attributed this result to large free-free optical depths Although this ratio is considerably smaller than the uncor- in the more compact, generally more luminous galaxies. Cor- rected ratio, we find that rc is still two orders of magnitude rection for this effect decreases the scatter in q considerably larger than the expected thermal value, with the LINERs show- ( see Fig. 5 of Condon et al. 1991 ) and suggests that the infrared ing the larger excesses (H n: 54, S: 66, and L: 151 ). The large and radio emission originating on the subarcsecond scale in values of rc are probably due to a combination of two effects: most of these LIGs (except perhaps for some of the Seyfert ( 1 ) most likely, the reddening determined from optical emis- 2 galaxies) is produced by starbursts. However, as Lonsdale, sion fines are underestimates of the actual amount of dust, and Smith, & Lonsdale ( 1993) recently discovered, this result does (2) nonthermal radio processes associated with supernova ex- not exclude the possibility of milliarsecond-scale AGN cores plosions and their remnants, shock ionization, or directly re- with log F* £ 5 in many (and perhaps all) of these objects, lated to the AGNs are present in the cores of these objects. One contributing a small ( ~ 12% ) fraction of the total radio power. or both of these effects is affecting LINERs more than the other The imphcation of this important result will be discussed in LIGs. The nature of LINER LIGs will be discussed in more §4.1.2. detail in § 4. In Figure 21 a, we have plotted the ratio of 20 cm continuum fluxes to Ha line fluxes for most of the objects in our sample. The value expected for free-free emission at p = 1.49 Ghz from 2.10. Morphological Properties and Presence of Companions a 10,000 K extinction-free gas is 1.0 X 1012 mjy erg-1 cm2 s (Kaufman et al. 1987). Figure 2\b shows this same ratio after Galaxy interactions are well known to play an important correcting the Ha fluxes for extinction using the values of E(B role in luminous infrared galaxies (Lonsdale et al. 1984; Cutri
© American Astronomical Society • Provided by the NASA Astrophysics Data System > r-\—I 198 VEILLEUX ET AL. Vol. 98 with an asymmetric or distorted appearance, but no evidence of a close-by companion; IAC = 3, galaxies with an ongoing interaction as judged from the presence of two overlapping or nearby galaxies; IAC = 4, advanced merger systems as indi- cated by the presence of tidal tails or shells around a single stellar system. The interaction classes of 92 objects belonging to the BGSs were extracted from the tabulations of Sanders et al. ( 1991 ) and Tinney et al. ( 1990). The interaction classes of nine objects from the WGSs were also included in the analysis. Our group is presently involved in a multiwavelength imaging study aimed at determining more accurately the stage of in- teraction of many of these objects. As in previous studies, we find a strong correlation between infrared luminosity and interaction class among the objects of the BGSs. The mean IAC of the objects in the log (Lir/L0) bins 10-11, 11-12, and above 12 are 2.53, 2.90, and 3.62, respec- tively. A weaker but significant correlation is also observed be- tween spectral types and interaction class in the sense that
Fig. 19.—Dereddened continuum colors as a function of the equiva- lent widths of Mg I b for each spectral type. The meaning of the symbols is the same as in Fig. 3.
& MacAlary 1985; Sanders et al. 1987; Vader & Simon 1987; Telesco, Wolstencroft, & Done 1988; Hutchings & NefF 1988; Jones & Stein 1989; Lawrence et al. 1989; Leech et al. 1989, 1994; Annus, Heckman, & Miley 1990, hereafter AHM90; Melnick & Mirabel 1990; Rowan-Robinson 1991 ). In order to address the issue of galactic interaction in our sample, we used the definition of Tinney et al. ( 1990) for the interaction class ( IAC ) : IAC = 1, isolated objects with no extended tails and no companion within three optical diameters; IAC = 2, galaxies
log^/L,,) Fig . 21.—Logarithmic radio-Ha flux-density ratios as a function of the Fig. 20.—Logarithmic FIR-radio flux-density ratios as a function of infrared luminosities for each spectral type using the observed Ha fluxes the infrared luminosities for each spectral type. The meaning of the sym- (top panel), or using the dereddened Ha fluxes (lowerpanel). The value bols is the same as in Fig. 3. expected for free-free emission from a 10,000 K extinction-free gas is 12.
© American Astronomical Society • Provided by the NASA Astrophysics Data System No. 1, 1995 LUMINOUS INFRARED GALAXIES. II. 199 AGNs and especially Seyfert 2 galaxies are more advanced merger systems than H n objects (IAC = 3.17, 2.91, and 2.78 for Seyfert 2s, LINERs, and H n galaxies, respectively). A K-S test indicates that the probability that the IAC distributions of H ii LIGs and AGN LIGs are drawn from the same distribu- tion is only 0.002. However, this result was expected since the proportions of AGN and Seyfert 2 galaxies increase with infra- red luminosity (§ 2.2). In an attempt to minimize luminosity effects, we divided our sample into the log {L^/Lq) bins 10- 11, 11-12, and above 12. We find a marginally significant difference (R[null] = 0.05) between the IAC distribution of H II LIGs and that of AGN LIGs when log (Lir/L0) = 11-12. Unfortunately, the number of objects in the other two lumi- nosity bins is not sufficient to run statistically meaningful K-S tests. The fact that the IAC-Lir correlation is stronger than the IAC-spectral type correlation suggests that the infrared lumi- nosity is the main driving parameter in these correlations (see §4.3). We also searched for any variations in the [O m] X5007 line widths as a function of the stage of interaction. No significant trend was observed. A similar result was found by Leech et al. ( 1989) using the Ha and [N n] line widths of the H n galaxies of their sample. Finally, we calculated the average equivalent width of the Ha emission line as a function of the interacting class IAC (Fig. 22). Differences were observed between the various classes: 42, 81, and 67 Á for galaxies with IAC = 2, 3, and 4, respectively (only two objects belong to IAC = 1 ). The differences between IAC = 2 and IAC = 3 may be significant (/"[null K-S] = 0.09) but the others are not (Ftnull K-S] = 0.6-0.7). These numbers can be compared with the results of Keel et al. (1985) who found that the median nuclear Ha equivalent width of single galaxies is roughly 8 A, while for 0 1 2 interacting galaxies it is approximately 25 Â. The strongly in- log[EW(Ha)] Â teracting (IAC = 3 and 4) LIGs of our sample do indeed show Fig. 22.—Distribution of the Ha equivalent widths in emission as a stronger Ha emission than the isolated objects of Keel et al. function of the interaction class. Galaxies with an asymmetric or distorted ( 1985). Both Keel et al. and Kennicutt et al. ( 1987) noticed appearance, but no evidence of a close-by companion have IAC=2; galax- that the average EW(Ha) decreases with projected separation ies with an ongoing interaction as judged from the presence of two over- lapping or nearby galaxies have IAC=3; and advanced merger systems as of the pairs. It may therefore be surprising to find that merged indicated by the presence of tidal tails or shells around a single stellar sys- systems (IAC = 4) generally have smaller EW(Ha) than sys- tem correspond to IAC = 4. tems with double nuclei (IAC = 3). However, it is important to note that equivalent widths of a number of the objects with IAC = 4 may be affected by the presence of an active nucleus. log (Lir/Lo) < 12, and open squares are systems with Moreover, systems in this interaction class are sometimes log (Lir/L©) <11. First, we find that many of the double nuclei difficult to difierentiate from objects in the lower interaction have ambiguous spectral types in the sense that the line ratios classes and so errors in the classification are likely. In contrast, in these objects do not correspond to the same spectral type in Leech et al. ( 1989) did not see a difference between the equiv- all three diagrams of V087. This result suggests that a mixture alent widths of interacting and noninteracting LIGs but this of ionization processes (e.g., photoionization by hot stars and apparent discrepancy may be attributed to the lack of strongly shock ionization, or photoionization by hot stars and an active interacting objects in their sample relative to the sample of nucleus) are taking place in the cores of these objects. Another Keel et al. ( 1985 ) and Kennicutt et al. ( 1987 ). important result is the presence of two Seyfert 2 galaxies (NGC Systems with double nuclei (LAC = 3 ) were investigated fur- 5256NE = Mrk 266NE and NGC 7592W) and a number of ther in an attempt to quantify the effects of galaxy interactions LINERs among this sample. This result shows that, at least in in these objects. Figure 23 shows the line ratios of the 25 sys- a few cases, the formation of active nuclei precedes the final tems ( 19 BGSs and 6 WGSs) with double nuclei for which we merger phase of the present galactic interaction. could measure the line ratios in both galaxies. Each physical pair is indicated by two data points joined by a line. Filled sym- 2.11. Infrared Spectral Properties bols are ultraluminous infrared galaxies [log (Lir/Lo)>12], The infrared spectral properties of the various classes of squares with an “X” in the middle are objects with 11 < LIGs were investigated. We used the definitions of Dahari &
© American Astronomical Society • Provided by the NASA Astrophysics Data System > r-\—I 200 VEILLEUX ET AL. Vol. 98
log([SII]6716+6731/Ha) log([SII]6716+6731/Ha)
Fig. 236 Fig. 23.—Dereddened flux ratios for double nucleus systems in (a) the BGSs sample and (6) the WGSs sample. The meaning of the symbols and the solid lines is the same as in Fig. 6.
De Robertis ( 1988) for thecolor indices [a! = -log^o/ The objects in our sample which belong to the BGSs were ^25)/log(60/25),a2 =-log(W^6o)/log( 100/60)] andfor found to have average aua2, IRCE, and C60 of-2.44, -0.77, 2 the “infrared color excess” {IRCE = [(ai + 2.48) + (a2 + 1.27, and 1.66, respectively. Differences in the selection criteria 1.94)2]0 5}. The infrared color excess is a measure of the devi- of the objects in the warm sample resulted in significantly ation from colors of nonactive spiral galaxies ( aj = — 1.48 and different average infrared properties: «i = -1.74, a2 = —1.01, a2 = -1.94; Sekiguchi 1987). The “spectral curvature” as de- IRCE= 1.30, and C60= 1.22. A tendency for the infrared colors fined by Condon et al. (1991; €60=«! — c^) was also used in of Seyfert galaxies to be warmer than those of H n galaxies is the analysis. well known to exist in both optically and infrared selected ob-
© American Astronomical Society • Provided by the NASA Astrophysics Data System 19 95ApJS. . .98. .171V 6 7 that theformationofanactivenucleuscannotbe sole the finalenergybudgetwillbediscussedin§4.1.2.Thepres- tween theinfraredcolors(dust temperatures)andtheintensity ratios [Oi]X6300/H«and m]X5007/Hßinourinfrared- Taniguchi (1992),wedonot findanystrongcorrelationbe- ence ofthesecorrelationsamongH11LIGssuggesthowever (Sanders 1992).Therelativeimportanceoftheseprocesses in lactic interaction.Astheinteractionproceeds,intensestarfor- sample. consequence oftheL^-zcorrelationourflux-limited frared luminosityandthea^-redshiftcorrelationissimply a driver ofthesecorrelations.Inthisgalacticinteraction sce- an increaseoftheinfraredluminosityanddusttemperature forming inthemergersystem.Alloftheseprocessesresult in luminous objectsgenerallyareatamoreadvancedstageofga- based ontheresultsdiscussedin§2.10,namelythatmore nario, theimportantparameterinthesecorrelationsis in- sion isconvertedintoshocks,andanactivenucleusmaybe mation istakingplace,thekineticenergyofgalacticcolli- of theirsample.Anotherexplanationforthesecorrelationsis possibility basedonthefactthattheir“extremestarbursts” be understoodifdusthasbeengraduallycoohngdowndueto sample; §2.2)didnothavehotterdustthantheotherstarbursts (which theyinterpretastheyoungeststarburstgalaxiesintheir ageing ofthestarsinstarbursts.However,theyrejectedthat jects (e.g.,Mileyetal.1984;Miley,Neugebauer,&Soifer1985; properties. tween infraredluminosityandredshift(seePaperI,Fig.3) redshift wasfoundinthesampleofAllenetal.(1991).The makes itdifficulttodeterminewhethertheinfraredluminosity existence inourflux-limitedBGSssampleofacorrelationbe- correlate withredshift.Asimilarcorrelationbetweenaand and thevaluesofamongBGSsorWGSsobjectsdonot lations. NoneofthesecorrelationsareobservedintheWGSs, or theredshiftisdrivingcorrelationsinvolvinginfrared No. 1,1995LUMINOUSINFRAREDGALAXIES.II.201 BGSs doesnotsignificantlyaffectthestrengthofthesecorre- 2 X10~,respectively).ExcludingalloftheAGNsfrom objects intheBGSsareconsidered(P[null]=5X10and observed toincreasewithinfraredluminositywhenonlythe of theWGSsobjects.Indeed,aandIRCE(butnotC60)are of awithinfraredluminositybutthisisduetothepresence al. 1987;Allenet1991).Ourcombined(BGSs+WGSs) colors ofIRASgalaxiesvarysystematicallywithinfraredlumi- sample doesnotshowanysystematictrendintheaveragevalue creases withincreasinginfraredluminosity(seealsoSoiferet respectively. nosity inthesensethatSóo/^íooincreasesandS12IS25de- LIGs: «!,a>IRCE,andC60=-2.48,-0.81,1.28,and1.62, more similartothoseofHngalaxiesthanSeyfert LINER propertiesgenerallyhaveinfraredwhichare served inoursample:«i,«2»IRCE,andC60=-1.72,-0.59, Dahari &DeRobertis1988).Thesedifferenceswerealsoob- Osterbrock &DeRobertis1985;deGrijp,Miley,Lub1987; -0.95, 1.20,and1.49forHnLIGs.Interestingly,objectswith 2 2 2 1.67, and1.07fortheSeyfert2LIGswhiletheyare-2.10, 2 In contrasttoMazzarella&Bothun(1989)andMouri & As discussedbyAllenetal.,thea—redshiftcorrelationcan Soifer &Neugebauer(1991)foundthatthemeaninfrared 2 © American Astronomical Society • Provided by theNASA Astrophysics Data System -8 -6 any spectraltype. of thesymbolsissameasinFig. 3.Thereisnostrongcorrelationfor and 0.7fortheH11galaxies,LINERs,Seyferts).Inthis (only presentamongtheH11galaxies;Pfnull]=0.003,0.3, LINERs andSeyfert)ortheIRASfluxratioFt60]/FT100] ity (jP[null]=10,0.03,and0.06fortheH11galaxies, weaker) correlationsareobservedamongtheinfrared-selected optical-to-infrared luminosityratioandtheinfraredluminos- Seyfert 2galaxies(Pfnull]=0.08and0.0007,respectively). (Mazzarella etal.1991).Perhapssurprisingly,similar(but duce far-infraredemissionwiththewarmestdusttemperatures result suggeststhatthemostactivestar-formingregionspro- lent widthstendtohavelowF[12]/F[25]andhigh.F[60]/ tical andinfrared-selectedH11galaxieswithlargeHaequiva- ( 1991)inasampleofopticallyselectedstarburstgalaxies.Op- equivalent widthsobservedbyMazzarella,Bothun,&Boroson we confirmthecorrelationsbetweeninfraredcolorsandHa selected sampleofH11galaxies(Figs.24and25).However, FflOO] (P[null]=0.006and10,respectively;Fig.26).This Fig. 24.—/ÆÆS'colorsasafunction of[01]A6300/Ha.Themeaning Figure 27showsthewell-knowncorrelationsbetween 19 95ApJS. . .98. .171V -3 -17 tinuum. gests thatthereddeningcorrection derivedfromtheemission lines mayoverestimatetheactual extinctionoftheopticalcon- tinuum luminositiesarecorrectedfordustextinctionusing the lesser extent,LINERLIGs(P[null]=0.06)todecrease at the colorexcessofHngalaxies(P[null]=10)and, to a dust temperatureisassociatedwithlargeinfraredemis- been interpretedinthepastasanindicationthathighglobal was appliedtothecontinuumluminosity.Thiscorrelation has ing ofthesymbolsissameasinFig.3.Therenostrongcorrelation strong positivecorrelationbetweenE(B-V)andL(4861 )/ emission-line Balmerdecrements(Fig.28).Theexistence of a large logL(4861)/Lirisconsistentwiththishypothesis(Fig. sion orsmallopticalcontinuumextinction.Thetendency for power ofthecontinuumat4861Á.Noreddeningcorrection for anyspectraltype. 27 ).Thefirsttwocorrelationsessentiallyvanishwhenthecon- as Pi4861)X4861whereP(4861)isthemonochromatic figure, theopticalcontinuumluminosity,L(4861),isdefined 202 Lir (P[null]=10whenconsidering alltheobjects)sug- 0 Fig. 25.—IRAScolorsasafunctionof[Om]X5007/Hß.Themean- © American Astronomical Society • Provided by theNASA Astrophysics Data System VEILLEUX ETAL. jects. In§2,wefocussedonthepropertiesofnucleargas observed amongHngalaxiesandpossibly alsoamongSeyfert2galaxies. sion. Themeaningofthesymbolsis thesameasinFig.3.Correlationsare {R <2kpc);wewillnowdiscussthebehaviorofmanythese these objectscanbeanexcellentprobeoftheactivenucleion reveal somethingabouttheenergysourcelurkingintheseob- properties asafunctionofthedistancefromnucleus.A natural toexpectthattheextendedlineemissioninLIGswill much smallerscale(seereviewWilson1991).Byanalogy,itis shown thatthecircumnucleargassurroundingcoresof continuum colors(see§2.8). luminous infraredgalaxieshavesomewhatbluerdereddened respectively). Thisresultmaybeduetothefactthatmore colors, (C6563/C4861)o(P[null]=0.08and0.09, IRCE tobelargerinobjectswithbluerintrinsiccontinuum Fig .26.—IRAScolorsasafunction oftheequivalentwidthHainemis- Recent studiesofoptically-selectedactivegalaxieshave Finally, wefindthatthereisaweaktendencyforand 2 3. SPATIALINFORMATION Vol. 98 19 95ApJS. . .98. .171V mined fromtheemission-Une Balmerdecrement(see§2.1). joining doublenucleiratherthanalongthemajoraxisof the ber ofobjectsfromwhichwewereabletoextractspatialinfor- timized toobtainspatialinformationontheobjectsof our individual galaxies.ThisfactexplainstherelativelysmaUnum- excess asafunctionoftheoptical-to-infraredluminosityratio.Themean- mum ofobjects:theshtwasgenerallypositionedalong Une introduces abiasinthissubsample,favoringnearbylow-lumi- the positionangleofshtfortheseobservations.One can with theirredshifts,infraredluminosities,spectraltypes, and total of23objectsfromoursamplecouldbeusedforthisexer- served amongtheH»galaxiesinallthreepanels. mation. ing ofthesymbolsissameasinFig.3.Anegativecorrelationob- sample butrathertoobtainnuclearinformationofamaxi- see fromthistablethattheconditionforextendedemission cise. ThenamesofthesegalaxiesareUstedinTable6along nosity objects.Notethatthedata-takingprocedurewasnot op- No. 1,1995 Figure 29showstheradialvariations ofE(B-F)asdeter- Fig .27.—Infraredluminosity,IRAS60-to-100¿onfluxratioandcolor © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.1. Reddening ^gC^eei/^ir) LUMINOUS INFRAREDGALAXIES.II. A strongpositivecorrelationisobserved inthelowerpanel. Balmer decrements.Themeaning of thesymbolsissameasinFig.3. ities havenowbeencorrectedfor dust extinctionusingtheemission-line excess inthecenterofgalaxyissignificantlylessthanout- ( Scovilleetal.1986,1989;Solomon1990;Radfordetal. axy IR1541+28andtheLINERsNGC12041525+36) side ofthenucleusoccuramongthreeAGN(theSeyfert2gal- concentration isconsistentwiththecompactdistributionof at Ræ3kpcsometimesreachesvalueslessthanhalfthe generaUy decreasesoutwardfromthenucleus.Theextinction tion numberinTable6.Irrespectiveoftheirinfraredluminos- molecular gasinmanyoftheseluminousinfraredgalaxies amount foundinthenuclearregion.Thishighdegreeofdust ities, theamountofreddeninginobjectsthissubsample The numbersnexttotheprofilescorrespondidentifica- ments outsideofthenucleusissameasin(i.e., For simplicity,weassumedthattheintrinsicBalmerdecre- out oftheAGN).Thisassumptiondoesnotaffectourresults. [Ha/Hßjo =2.85inandoutoftheHiinuclei3.1 1991). Fig. 28.—Sameas27,except that theopticalcontinuumluminos- Interestingly, invertedreddeningprofilesinwhichthecolor ïog^eeiAr).) 203 19 95ApJS. . .98. .171V In mostobjects,thecolorexcessdecreasesawayfromnucleus. nuclear valuesandthenumberscorrespondtoobjectslistedinTable6. therefore consistentwiththeevolutionaryscenarioinwhich but innoHngalaxies.Apossibleexplanationforthesein- H iiobjectsevolveintoAGNsaftershreddingmostoftheir expelled ordestroyedbytheAGN.Theseobservationsare verted profilesisthatthedustincenterhasbeenpartially 204 VEILLEUXETAL.Vol.98 Fig. 29.—Radialprofilesofthecolorexcess.Theasterisks(*)are Number 3 23 22 21 20 9 4 7 6 5 8 3 2 (1) 18 17 19 16 13 12 15 14 11 10 MixedlistofobjectsfromtheBGS andWGS,notinRAorder. MCG+03-60-036 MCG-03-04-014 NGC 7674 Zw 475.056 IR 22114-1109 NGC 5953 NGC 7591 ESO 602-G025 Zw 247.020 NGC 7679 IR 15304+3017 IR 18293-3413 Zw 453.062 NGC 7130 ESO 286-IG019 IR 15250+3609 UGC 8696 IR 22220-0825 NGC 1204 IR 15418+2840 IR 13446+1121 NGC 660 NGC 34 © American Astronomical Society • Provided by theNASA Astrophysics Data System Name (2) 3 Long-Slit Sample TABLE 6 (km/s) 16360 10470 19480 12900 16220 11580 18060 5490 4970 2070 7450 7760 4810 4320 4490 8750 8150 5400 7560 9890 6910 5860 cz (3) 820 log(L) ir 11.44 11.51 11.21 10.40 11.61 11.00 11.53 11.18 11.28 11.71 11.25 11.05 11.22 11.99 11.32 11.98 12.11 10.86 10.91 10.37 11.39 10.96 11.43 (L) 0 (4) Spectral Type S2: S2 S2 S2 S2 H: S2 (5) H: S2 S2 L: L: L: L: H H H L L L L L L 133 PA (6) 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 68 90 doubles). the extractionaperturefrom nucleusthatincreases(generally between eachdatapointwhile,inthe lowerpanel,itisthemid-distanceof top panel,thesizeofextraction apertureincreases(generallydoubles) cleus (lowerpanel).Inbothpanels,theasterisks(*)marknuclear val- size oftheextractionaperture(toppanel),anddistancefrom nu- ues andthenumberscorrespondtoobjectslistedinTable6.In the the nucleus.Thesevariationscanbeunderstoodifacircum- nuclear starburstissurroundingaAGNline-emitting region-like inthecircumnucleargas.ThefineratiosofNGC 453.062, NGC5953,and7679.Thelineratiosof 7679 behaveinasimilarfashionwiththeexceptionof size oftheaperture.ThemostnoteworthyexamplesareZw subsample havelineratioswhichchangesignificantlywiththe [S II]/HaratiowhichremainsHnregion-likeinandoutof 5953 andZw453.062areAGN-likeinthenucleusbutHn sizes areshowninFigures30-32.Someoftheobjectsthis We willreturntothisdiscussionin§§4.2and4.3. in thenucleioftheseobjects(Leechetal.1989;Keel1993). however, thatcomplexopticaldeptheffectsmayproducein- that thenucleardustcontentinSeyfertgalaxiesshouldbe verted dustprofileswithoutinvokingasmalleramountof lower thanthatinHngalaxies,aresultfound§2.1.Note, nuclear dust(e.g.,Sandersetal.1988a).Thisscenariopredicts Fig. 30.—[Om]X5007/Hßvs.[Nii]A6583/Haasafunctionofthe The variationsofthelineratiosasafunctionaperture 3.2. SpectralClassification > No. 1, 1995 LUMINOUS INFRARED GALAXIES. II. 205 shocks caused by the interaction of the outflowing nuclear gas with the ambient material. This scenario could also explain the ionization gradient in our objects.
3.3. Densities The density profiles were measured in 16 objects of our sam- ple using the [S n] A6731/A6716 ratio. The results are pre- sented in Figure 33. Measurements near the low-density limit -3 {ne^\50 cm ) should be treated with caution. Complex den- sity variations are observed in all of these objects. However, there is a weak trend for lower densities to be found at larger distances from the nucleus. One notable exception to this rule is MCG -03-04—014 in which the density is near the low- density limit at the nucleus but reaches 1400 cm-3 at R « 1.5 kpc. Less extreme examples are the profiles of IR 1525+36 and NGC 7674. The radial density profiles of AGNs were not found to be different from those measured in H n objects apart from a generally higher normalization factor (see § 2.4). Unfortu- nately, the density profiles could not be determined for any of the ultraluminous infrared galaxies of our sample, so no state- ment can be made about the reported variations in the density profiles of LIGs as a function of infrared luminosity (HAM90; see Veilleux et al. 1994, however).
Fig . 31.—[O m] X5007 /H0 vs. [S H ] XX6716,6731 /Ha as a function of the size of the extraction aperture {top panel), and the distance from the nucleus {lower panel). In both panels, the asterisks (*) mark the nuclear values and the numbers correspond to the objects listed in Table 6. In the top panel, the size of the extraction aperture increases (generally doubles) between each data point while, in the lower panel, it is the mid-distance of the extraction aperture from the nucleus that increases (generally doubles).
region, as in the cases of other LIGs and some optically selected AGNs (e.g., Mrk 231 and NGC 7469; Sanders et al. 1988b; Wilson et al. 1991 ). Evidence for circumnuclear starbursts in many of our objects also comes from the strength of the ab- sorption features outside of the nuclei (§3.6). The presence of these circumnuclear starbursts may explain the smaller frac- tion of AGN LIGs found in fainter IRAS surveys ( Lawrence et al. 1989; Leech et al. 1989; Rowan-Robinson 1991 ). In these studies, the ultraluminous infrared galaxies are typically 3 times more distant than objects from the BGSs, so the aperture includes more of the circumnuclear (H n region-hke) emission than in the more nearby objects. This result emphasizes the fact that a constant linear-size aperture is crucial when classi- fying the nuclear spectra of LIGs using emission-line ratio di- agnostics. On the other hand, the line ratios in the nuclei of IR 1829-34, MCG -03-04-014, MCG +03-60-036, and ESO Fig. 32.—[O hi] A5007/H/? vs. [O i] X6300/Ha as a function of the 286-IG019 are H n region-hke but become LINER-like at size of the extraction aperture {top panel), and the distance from the nu- larger distances from the nucleus. A similar effect was observed cleus (/o wer panel). In both panels, the asterisks (*) mark the nuclear val- by AHM89 and Heckman, Armus, & Miley ( 1990, hereafter ues and the numbers correspond to the objects listed in Table 6. In the top panel, the size of the extraction aperture increases (generally doubles) HAM90) in M82. They explained this type of ionization struc- between each data point while, in the lower panel, it is the mid-distance of ture in the context of a supemovae-driven wind model in the extraction aperture from the nucleus that increases (generally which the circumnuclear gas colhsionally ionized by strong doubles).
© American Astronomical Society • Provided by the NASA Astrophysics Data System 19 95ApJS. . .98. .171V 3 -3 3 6-3 both [Ohi]A5007andHawereexamined.Inspiteofthelarger than thelinewidth.Thespatialvariationsofwidths of Figures 35and36.Wenotea generaltendencyforthe[Om] and stellarHamakethewidth ofHamoreuncertainthanthat prevents usfromstudyinganylineprofileparametersother of [Oin].Theresultsthese measurementsarepresentedin strength ofHa,blendsthislinewith[Nil]XX6548,6583 data withsignal-to-noiseratiohigherthaninthepresent data tion, hardeningoftheAGNionizingfield,metallicitygradi- gradients in[Om]X4363/A5007(seeFig.33).Shockioniza- of theseobjects. mine ifpositivetemperaturegradientsareacommonfeature and takenatanumberofpositionanglesareneededtodeter- sured inonlyahandfulofotherLIGs(e.g.,HAM90).New produce thesetemperaturegradients. ents, oracombinationoftheseprocessesappearmorelikelyto temperatures atlargerdistancesfromthenucleus.Thisisespe- NGC 7674.TheirtemperatureprofilesarepresentedinFigure line ratiosinandoutoftheirnuclei:IR2211-11 carried outforonlytwogalaxies,bothofwhichhaveSeyfert2 of oursample,astudythetemperaturegradientscouldbe 34 inthecaseswheren=10(probablymorerealistic)and cm ).Densityvariationsdonotseemtobeableexplainthe ues largerthan30,000KatR>5kpc(assumingn=10 cially clearinIR2211-11wherethetemperaturereachesval- ble 6. the nuclearvaluesandnumberscorrespondtoobjectslistedinTa- 10 cm.Inbothobjects,thereisatendencytofindlarger e e 206 The ratherpoorspectralresolutionofourdata(~8-10Á) The spatialvariationsofthe[Om]X4363lineweremea- Due tothefaintnessof[Om]X4363innearlyallobjects Fig. 33.—Radialprofilesoftheelectrondensity.Theasterisks(*)are © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.4. Temperatures 3.5. LineWidths VEILLEUX ETAL. 36- tron densities(10andcm).Theasterisks(*)arethenuclearvalues. [O in]X4363/X5007fluxratio.Thetemperaturesaregivenfortwoelec- tend topullinmoreoftheemissionwingsawayfrom side ofthenucleus. broadening associatedwithPoissoniannoise(noisiersignals galaxies NGC34and7674.Wecannotcompletelyrule Table 6.Notethat,inmanycases, thelinewidthsreachamaximumout- (*) arethenuclearvaluesand numberscorrespondtotheorderin out thepossibilitythatthiseffectisdueinparttonumerical widths areexamined.Theonlyobjectswhichclearlyhave smaller [Oin]widthsoutsideoftheirnucleusaretheSeyfert2 line widthstoreachamaximumoutsideofthenucleus.This effect issomewhatweakerwhenthemoreuncertainHaline Fig. 34.—Radialprofilesoftheelectrontemperaturederivedfrom Fig .35.—Radialprofilesofthe[O m]X5007linewidths.Theasterisks _1 FWHM([0III]) kms Vol. 98 19 95ApJS. . .98. .171V -1 is valid,thestudyofradialvariations ofthestrengththis continuum byafeaturelessproducedanAGN in §2.7tobeconsiderablysmallerthantheequivalentwidths ture oflarge-scalebipolaroutflowsfromthenucleus.Data of therein). WiththeexceptionofremarkableobjectNGC feature withdistancefromthe nucleusmayhelpdeterminethe or byhot,youngstarscanexplain thisresult.Ifhypothesis observed innonactivespiralgalaxies.Dilutionoftheold-star LIGs. of linesplittinginthecircumnuclearnebulaeoursample of higher spectralresolutionareneededtoconfirmthepresence objects arethereforeinterpretedasbeingthekinematicsigna- The broadnon-Gaussianprofilesoutsidethenucleusofthese plitude wouldbedifficulttodetectattheresolutionofourdata. tively commonfeatureinthehandfulofLIGsforwhichhigh- where twoormoreemission-linecomponentshavingdifferent turbulent motion.Wespeculatethatthebroadprofilesoutside by organized,large-scalebulkmotionratherthanchaotic, termediate radiiinabout4ofthese12galaxiessuggestthatthe to confirmtheseresults. served tobelessthan~400kms.Linesplittingofthisam- ippenko &Sargent1992;Veilleuxetal.1994,andreferences resolution kinematicdataexistintheliterature(e.g.,Ulrich velocities arepresent.Suchextranuclearlinesplittingisarela- peak andsobroadenthefittedlineprofile).Observationsat of thenucleusareproducedby(unresolved)linesplitting larger linewidthsobservedoutsideofthenucleusareproduced higher signal-to-noiseratiosandspectralresolutionareneeded the nuclearvaluesandnumberscorrespondtoorderinTable6. 3079, thevelocityseparationsinalloftheseobjectswereob- 1978; Axon&TaylorBlandTully1988;HAM90;Fil- No. 1,1995 The MgIbequivalentwidthsmeasuredinLIGswerefound Nevertheless, thehighlynon-Gaussianprofilesfoundatin- Fig. 36.—RadialprofilesoftheHalinewidths.Theasterisks(*)are © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.6. StellarAbsorptionFeatures _1 FWHM(Ha) kms LUMINOUS INFRAREDGALAXIES.II. 7 typically foundinnon-activespiral galaxies(~4A).Thenuclearvalueof Table 6.TheMgibequivalentwidths areloweratallradiithanthevalue isks (*)arethenuclearvaluesand the numberscorrespondtoorderin EW(Mg Ib)isalsooftensmallerthan thatintheimmediatesurroundings. the featurelesscontinuumproducedbyAGNor the dilutionofoldorintermediate-agestarcontinuumby the circumnuclearmeasurements.Thisresultprobablyreflects tral types,thenuclearequivalentwidthsareoftensmallerthan be anothersourceofvariationsinEW(Mgib)(Edmunds and 38donotshowanytrendswithinfraredluminosityor discussed in§3.7.Metallicitygradientsthehostgalaxymay nuclear spectraltypes.Indeed,regardlessofthespec- The issueofradialvariationsthecontinuumcolorswillbe expected tobeflatorevenrisingtheblue(Bicaetal.1990). weak Mgibabsorptionfeatureisentirelyproducedbythered tended, youngstarbursts(age^10yr).Inthisscenario,there supergiants (Bicaetal.1990).Inbothcases,thecontinuumis is noneedforanunderlyingoldstellarpopulationbecausethe is thatweareseeingtheredsupergiantphaseofspatiallyex- in mostoftheobjectsoursubsample.Anotherexplanation tinuum isextendedand,consequently,thatcircumnuclear starbursts areimportantcontributorstotheopticalcontinuum galaxies (~4Á;Heckmanetal.1980;Stauffer1982).Thisre- than thevaluesmeasuredinnucleiofnormal,fieldspiral sult suggeststhatthesourceofdilutionoldstellarcon- lent widthsofoursubsampleLIGsareconsiderablylower essentially allofthenuclearandcircumnuclearMgIbequiva- bursts suggestedbyCondonetal.1991toexistinmanyultra- from ourdataarepresentedinFigure37.Note,firstofall,that using thismethodalone). luminous infraredgalaxiescannotbedifferentiatedfromAGN pointlike AGNandextendedstarbursts(thecompactstar- size ofthecontinuumsourceandthereforedistinguishbetween 1989; DiazThomsen&Baum1987). Fig .37.—RadialprofilesoftheequivalentwidthsMgIb.Theaster- The radialEW(MgIb)andEW(Hiff)profilesofFigures37 All oftheradialEW(Mgi)profilesthatcouldbederived 207 19 95ApJS. . .98. .171V 9 galaxy (Fig.39),withatendencyforthecolorgradientsto be tent, Zw453.062),andtheHnobjectsIR1829-34MCG than 10yearold.Undoubtedly,dustisaffectingthecontin- red tobeproducedbyanunreddenedstellarpopulation less ple areredderinthenucleusthanoutskirtsofhost dust distributionisproducing differentialreddeningwhichis circumnuclear stellarpopulations. Theradialgradientofthe uum colorsofthenuclearregion and,toalesserdegree,the ies NGC7679,andIR1344+11(and,toalesserextent, IR subsample. WiththenotableexceptionsofSeyfert2galax- the lineemissioninthisobjectisproducedbyanAGN. triplet XX8542,8662equivalentwidths(Zw041.073[Hn], steeper inthereddernuclei.Thecontinuumcolorsareall too function ofdistancefromthenucleusforall23objectsin the sults. However,wecannotexcludethepossibilitythatsomeof unresolved activenucleushavedifficultiesexplainingthesere- kpc, and0.81Áat1.0-2.0kpc.Dilutioneffectssolelybyan (Can XX8542,8662)inIR1344+11wasfoundtobe4.99, long-slit datacouldbeextractedforonlythelastone.EW Zw 102.056[HII],andIR1344+11[S2/Hn],see§2.7), bursts preventsusfromaccuratelydeterminingthesizeof -03-04-014, thecontinuumcolorsofobjectsinoursam- b) variesfrom0.87Ainthenucleus,upto1.26at0.5-1.0 nuclear continuumsource,however. nuclear starburst.Contaminationbythecircumnuclearstar- 3.92, and7.33Áatadistancefromthenucleusof0.0-0.5,0.5- than thatintheimmediatesurroundings. 1530+30), theLINERESO602-G025(and,toalesser ex- The asterisks(*)arethenuclearvaluesandnumberscorrespondto 1.0, and1.0-2.0kpc,respectively.Forcomparison,EW(Mgi order inTable6.TheHßequivalentwidththenucleusisoftensmaller o 208 The continuumcolor,C6563/C4861,wasmeasuredas a Of thethreeobjectsforwhichwehavereliablenuclearCan Fig. 38.—RadialprofilesofEW(FIß)inthegalaxiesoursample. abs © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.7. ContinuumColors VEILLEUX ETAL. the nuclei. Table 6.Notethegeneraltendency fortheobservedcolorstoberedderin isks (*)arethenuclearvaluesand numberscorrespondtotheorderin source ofenergyresponsibleforionizingtheline-emittinggas tent withthishypothesis. NGC 660(L),1204L:),7591andESO286- than intheoutskirts.Theseresultssupportpresenceofan most oftheselocations(see§3.6andFig.37)arealsoconsis- IG019 (L:)maybecausedbythepresenceofayoungcircum- AGN and/orastarburstinthenucleioftheseobjects.On tinuum colorsinthenuclearregionofmostgalaxiesarebluer nuclear starburstregion.ThesmallerEW(MgIb)observedat other hand,thebluecontinuumcolorsoutsideofnuclei infrared luminosityorspectraltypesoftheobjects.Thecon- dereddened continuumcolorsisnotparticularlysensitiveto However, itisinterestingtonotethattheradialbehaviorof effects ofthestellarcontinuumbyblue,AGNcontinuum. the colorsofZAMS.IncasesSeyfert2galaxies NGC 34and7679(andperhapsalsotheLINER all, notethatsomeofthedatapointsinFigure40arebluerthan star clustersofvariousages(fromJacobyetal.1984).First The verticaldashedlinesinthisfigurerepresentthecolorsof dening effectsusingthemeasuredHa/Hßemission-lineratios. 7591 ),theextremenuclearcolorsareprobablyduetodilution the bluecontinuumproducedbystarburstingpopulation roundings, perhapsbecauseitisstronglyaffectedbythehard, dominating thecontinuumcolorprofiles.Inafewgalaxies, (in Hiigalaxies). nuclear continuumisanomalouslybluewithrespecttoitssur- power-law continuumproducedbytheAGNs(inSeyferts)or Fig .39.—Radialprofilesoftheobserved continuumcolors.Theaster- First, animportantdistinctionshouldbemadebetweenthe In Figure40,thecontinuumcolorswerecorrectedforred- 4.1. EnergySources 4. DISCUSSION C6563/C4861 Vol. 98 19 95ApJS. . .98. .171V _2 7 9 gion-like spectraisphotoionization byhotO-Bstars.Thede- tion thatthemainsourceof ionization inLIGswithHnre- trast, theproportionofLINERswasfoundtobeabout27% regardless oftheinfraredluminosity. Thereisverylittleques- ies amongtheAGNsincreasewithinfraredluminosity.Incon- ( SeyfertandLINER)spectrathefractionofgalax- ity intheseobjects. difficult questionoftheoriginlargebolometricluminos- and thenattempttoprovidefurtherconstraintsonthemore address theissueofnatureionizationsourceinLIGs (^10%; seealsoAHM90).Inthepresentsection,wewill first duced byLIGswhichisusedinionizingtheline-emittinggas this ratioratheruncertain,thefractionoftotalenergypro- Although correctionforreddeningeffectsmakesthevalueof observed atopticalwavelengthsisthereforelikelytobesmall less thantwicetheirinfraredluminosity(e.g.,Riceetal.1988; that thetotalemission-hneluminosityisabout30times Ta+[Nii](total) soL(total)æ10-10“^.Furthermore, Soifer etal.1987)wehavethatLb(total)^0.1-0.01L^. 0.0001 Li,,inmostoftheobjectsoursample.Theimaging ities andviolentoutflowsobservedinsomeoftheseobjects(see Ha luminosity(e.g..Binetteetal.1985;Ferland&Netzer since bothshockionizationorphotoionizationmodelspredict in LIGs(thereaftercalledthesourceofionization)and No. 1,1995 study ofAHM90foundthatLHa+[Niii(nucleus)~0.1 § 3.5and4.2).In2.3,wefoundthatLa(nucleus)^0.001- source ofenergypoweringthequasar-likebolometricluminos- sent thecontinuumcolorsofstarclusterswithages0(ZAMS),10,and in Table6.Theverticaldotted,short-dashed,andlong-dashedlinesrepre- terisks (*)arethenuclearvaluesandnumberscorrespondtoorder 1983) andthetotalbolometricluminosityofLIGsistypically HHo!ir ne 10 yr,respectively. H We foundin§2.2thatboththefractionofLIGswithAGNs Fig. 40.—Radialprofilesofthedereddenedcontinuumcolors.Theas- © American Astronomical Society • Provided by theNASA Astrophysics Data System 4.1.1. SourceofIonization LUMINOUS INFRAREDGALAXIES.II. can discriminatebetweenthis ionizationprocessandphoto- levich 1992)intheAGNLIGs isdifficulttoassessasthere jects maywellbephotoionizedbynormalhotstars.Filippenko relatively littleinformationavailable atthepresenttimewhich hot stars(“Warmers”;Phases2and3inthescenarioofTer- cess cannotexplaintheextended,circumnuclearLINERemis- the galacticnucleusofourobjectsand,consequently,this pro- tion areunlikelytobepresentoverextendedareasoutside of sion observedinsomeofourobjects. required toproduceLINERemissionbyO-starphotoioniza- are consistentwiththispicture.Inanycase,thehighdensities reahstic. Note,however,thatthelargernuclear[Sn]densities found inLINERLIGscomparedwiththoseofHnobjects LINER LIGs,highlyirregularanddustysystems,maynot be to explainLINERswithlarger[Oi].Thisprocessmaybere- cally selectedLINERsbuttheapplicationofthesemodels to sponsible forthelineemissionofsomewell-organized,opti- density-stratified environmentwithsolarabundancesmodi- in oursampleunexplained.Photoionizationbyhotstarsa fied bynormalgraindepletionwassuggestedShields(1992) mechanism leavesthespectrumofmostLINERLIGs by hot(T^45,000K)main-sequenceOstars.However,this where [On]X3727couldbemeasuredreliably,afewLINER definition usedinthepresentstudydoesnotexactlycorre- & Terlevich(1992)pointedoutthatLINERswith[Oi] LIGs werefoundnottobe“genuine”LINERs.Thesefewob- portant atthisstagetoemphasizeonceagainthattheLINER portance ofeachtheotherprocessesinAGNLIGs.Itisim- be combinedwiththoseofpreviousstudiestoaddresstheim- spond totheoriginaldefinitionofH80(§2.2).Incases axies ofLIGs(§2.10).Theresultspresentedin§§2and3can associated withdominantearly-typegalaxiesinX-rayclusters A6300/Ha ^\mayalsobeproducedthroughphotoionization rather thanthelate-type,morphologicallydisturbedhostgal- fact thatgalaxiesassociatedwithcoolingflowsaregenerally cooling flowscanbediscardedratherconfidentlybasedonthe ized byacombinationofsometheseprocesses. tion ofhot,high-metallicitystarslyingperhapsinadenseen- & Wang1985;Phillipsetal.1986;Fabian1986)orion- cooling accretionflows(Mathews&Bregman1978;Kent penko &Terlevich1992;Shields1992),(4)associatedwith vironment (Terlevich&Melnick1985;Terlevich1992;Filip- Sargent 1979;Heckman1981;Cowieetal.1983;Hu,Cowie, HAM90; Harwitetal.1987),(3)photoionizedbyapopula- bient mediumofthehostgalaxyorresultingfromcolli- ippenko 1985;V087;Ho,Filippenko,&Sargent1993),(2) sions (Koski&Osterbrock1976;Fosburyetal.1978;H80; pem 1984;PéquignotStasinskaBinette1985;Fil- shock ionizedbytheinteractionofoutflowinggaswitham- AGN continuum(Ferland&Netzer1983;FilippenkoHal- Almost certainly,opticallyselectedLINERsconstituteaheter- ogeneous classmadeofobjects(1)photoionizedbyaweak issue (seeHeckman1987andFilippenko1989forreviews). particularly inthegalaxieswithLINERspectra.Aconsiderable bate centersontheionizationprocessinAGNandmore amount ofworkoverthelast10yearshasbeendevotedtothis The importanceofphotoionizationbyaclusterunusually In theinfrared-selectedobjectsofoursample,emissionfrom 209 19 95ApJS. . .98. .171V 67 45 l2 jets insomeLIGs(e.g.,theLINERNGC3079;Irwin the AGNemissioncomesfromnullorpositiveradial gra- (see Figs.30-32).Thisratio is knowntobehighlydependent dient ofthe[Oin]\5007/Hßratioinsometheseobjects on theionizationparameter{U =densityofionizingphoton/ null orpositive[OIii]/Hß radialgradientsaretherefore ticularly trueinthecaseofshockionizationcausedbygalaxy produced fromaregionwhichisspatiallyextended.Thispar- phase. Ineithercase,theLINERemissionisexpectedtobe by dilutebremmstrahlungradiationemittedthehot-gas gas attheinterfaceofinteraction.LINERemissionispro- thermalized viashocks,producingveryhot{T^10-10K) the faintX-raytailofopticallyselectedQSOs(Sanderset be veryvaluableinthatcontextasadetectionofradiation tions outsidetheopticalwindowandintoinfrareddomain trons. profiles (§2.6).Thehighvaluesofr(20cm/Ha)inLINER and inthesampleofHAM90.Moreover,LINERemission was kpc inextent.SpatiallyextendedLINERemissionwasindeed encounters wheretheregionofinterfaceisexpectedtobemany duced inthe10-10Kpost-shockgasorphotoionized energy involvedinthelargerelativegasmotionisefficiently quence ofsuchviolentprocesses.Inthisscenario,thekinetic emission associatedwithshockionizationisanaturalconse- interaction ofnuclearoutflowinggaswiththecircumnuclear al. 1989). rule outanoverlapoftheX-raypropertiestheseobjectswith ionization. ThepresentupperlimitsonthehardX-rayfluxes dermine thepossibilityofWarmersproducingbulk above ~100keVfromtheseobjectswouldseriouslyun- too smallinthepresentstudyforanystatisticalanalysis.Mea- the sampleofLIGsforwhichwehavereliablemeasurements ization throughanabundantproductionofrelativisticelec- LIGs (see§2.9)maybeexplainedinthecontextofshock ion- found tobeparticularlyfrequentinadvancedmergers(IAC = observed inmanyofthenearbyLIGsoursample(§ 3.2) region (see§§2.6,2.10,3.5,andreferencestherein).LINER ically irregularasaresultofgalacticencountersand/orthe from ultraluminousinfraredgalaxies(e.g.,Rieke1988)donot (Maeder 1990).AsearchforhardX-raysinLIGswouldalso cover thepresenceofstrongstellarwindsfrommassivestars scenario. Spectroscopyatultravioletwavelengthsmayhelpun- & Seaquist1988)aredifficulttoreconcilewiththeWarmer length range(includingtheimportantCantripletfeature)is tinuum inthenuclearregionsofmanySeyfert2LIGs may providethebesttests.Detectionofwell-collimatedradio stars isaffectingthestrengthsofanythesefeatures.Observa- objects andtofindoutwhetherthepresenceofredsupergiant of dilutioneffectsbyafeaturelessAGNcontinuuminthese surements ofthiskindareneededtodeterminetheimportance of alargenumberabsorptionlinesspanningbroadwave- Warmer andAGNscenarios.Asdiscussedin§2.73.6, ionization byagenuineactivenucleus(asinthecaseoftheir 3 and4;see§2.10)inobjectswithbroademission-fine our sample(see§§3.6and3.7)canbeexplainedinboththe optically selectedcounterparts).Thepresenceofabluecon- electron densityocn~R~\Q .g., Ferland&Netzer1983).The 210 Additional supportforashockionizationorigintosomeof The nebulaeofmostLIGsareentitieswhichmorpholog- © American Astronomical Society • Provided by theNASA Astrophysics Data System VEILLEUX ETAL. =-3 -1 -32 26-1 n 62-1 [S H]XX6716,6731/Ha,and[OI] X6300/Ha. emission isconsiderablymoredifficulttoproducefromshock exists intheserelationsforoursampleofobjects. dict strongcorrelationsbetweenfinewidthsand[Oi]/Ha,[S tively highvaluesfortheparameters(e.g.,«100cm,^4= range ofshockconditionsareneededtoproducethehigh-exci- ionization thanLINERemission.Indeed,averyrestrictive II]/Ha, or[Nn]/Ha,butFigure41showsthatalargescatter of mosttheobjectsinoursampleevenifweuseconserva- value issmallerthanthereddening-correctedHaluminosities is theshockvelocity(inkms)(Binetteetal.1985).This ambient gas(incm),^4istheshocksurfacepcandV is ~2.4X\QnoAV]ergss,where«othedensityof photoionization andshockionizationarebothtakingplacein nario: theHaluminosityexpectedfromshockionization many oftheseobjects.Energyargumentsalsosupportthissce- not observedinLIGs(see§3.3andHAM90).Mostlikely, follows n(r)ocr~with«^2.Suchsteepdensityprofilesare AGN orWarmers)unlessthecircumnucleardensityprofile photoionized byanuclearsourceofhardphotons(beitan 10 pc,andV=300kms).Moreover,shockmodelspre- /«consistent withtheideathatcircumnucleargasisbeing 0 s s Fig. 41.—[Oin]X5007linewidths asafunctionof[Nn]X6583/Ha, Finally, itisimportanttoemphasizethattheSeyfert-like log([Sn]6716+6731/Ha) Vol. 98 19 95ApJS. . .98. .171V 5 36 -3 tances oforder~1kpc. wavelengths (Condonetal.1991).Forthisreason,optical the detectionofcompact(R^200pc),highbrightnesstem- region, isnotcompletelycoveredbymolecularclouds,so that plies thatthenuclearsource,asseenfromcircumnuclear acteristics ofthecircumnucleargasandstellarpopulation re- wavelengths exceptperhapsinthehardX-raysoratradio tion ofmoleculargaswhichisessentiallyimpenetrableatall presence ofagenuineAGN were farmorecommonamong perature {T^10K)radiocoresgenerallyattributedto the servations. Norrisetal.(1988,1990)foundforinstance that some oftheradiationemittedincenterleaksoutto dis- LIGs. Thisassumptionabouttheline-emittinggasinturn im- flect thedominantprocessestakingplaceinverycore of of LIGsheavilyreliesontheassumptionthatphysicalchar- studies whichattempttodeterminethecentralenergysource energy ofLIGsisembeddedinaverydensenuclearconcentra- found nocorrelationintheir sampleofLIGsbetweenthede- contrast, thedeepersurveyof Lonsdaleetal.(1993)recently LIGs opticallyclassifiedasAGNs thanamongtheothers.In of starburstsrelativetoAGNliesinthefactthatsource the othertwoscenariosmaybeimportantforlowerluminosity the starburstandAGNscenarios,butwillkeepinmindthat teracting systemandtheinfraredluminosityperunitHmass objects. axy-collision model).Wewillthereforefocusourattentionon is alsoinconsistentwiththislastscenario(Sandersetal.1991; lack ofcorrelationbetweenthetotalkineticenergyinin- diation fromanoldstellarpopulationstartstobreakdown galaxies. Atthesehighluminosities,thescenarioinvolvingra- see Condonetal.1991foranotherargumentagainstthegal- ( 1987)requiresthegalaxycollisionstobenearlyface-on.The (Thronson etal.1990),whilethescenarioofHarwit wit etal.(1987).Fromatheoreticalpointofview,allthese the largeinfraredluminositybytappingintokineticenergy the mainheatingprocessinLIGs.Thepossibilityofproducing tent withphotoionizationbyahardcontinuumof10-10 involved inviolentgalaxycollisionswasalsoexploredbyHar- al. 1985;Condonet1991),ortheoldunderlyingstellarpop- these grains.Theradiationfieldfromadust-enshroudedAGN cm medium(§§2.5and3.4). tron temperaturedeterminedinthe10Seyfert2LIGsofour models arerathersuccessfulatexplainingobjectswithlog(L/ ulation (Thronsonetal.1990)haveallbeensuggestedtobe (e.g., Sandersetal.1988a;Lonsdale,Smith,&Lonsdale The dilemmaconsistsinfindingthedominantheatsourceof tation spectrumofSeyfertgalaxies(e.g.,Binetteetal.1985; nosity ofLIGsisthermalradiationfromheateddustgrains. sample inwhich[Om]X4363wasdetectedareindeedconsis- nant ionizationprocessinSeyfertLIGs.Thevaluesoftheelec- Innés 1992).Shockionizationisthusunlikelytobethedomi- b L)^ 12.Therealtesthoweveristoexplaintheultraluminous No. 1,1995 2 1993), extendedorcompactnuclearstarbursts(e.g.,Riekeet ir 0 Until recently,thisassumptionwassupportedbyradioob- Observationally, thedifficultyinevaluatingimportance There isageneralconsensusthatmuchoftheinfraredlumi- © American Astronomical Society • Provided by theNASA Astrophysics Data System 4.1.2. SourceoftheLuminosity LUMINOUS INFRAREDGALAXIES.II. 67 -4 luminosity oftheLIGsinour samplecouldbepoweredbythe Wyse (1985)inthecaseofayoung10-10yr)starbursting luminosity, L(4861),is~5%ofthebolometricluminosity. tinuum insomeoftheseSeyfertgalaxiesisdifferentfrom H n starburst ifalloftheopticalcontinuum isindeedproducedby metric corrections(e.g.,Bruzual 1981):L(4861)/Læ stellar populationtakingintoaccounttheappropriatebolo- This ratiocanbecomparedwiththetheoreticalpredictions of ( 1991)showthatLlL^x~0.5andthereforethecontinuum results ofRiceetal.(1988),Soifer1987),andSanders luminosities ofourobjectsintobolometricluminosities. The published starburstmodels,weneedtotransformtheinfrared directly relatedtotheHnobjectsthanSeyfertgalaxies and LINERLIGs,thatmanyLIGsmaybemore that theaveragevaluesoflogL(4861)o/LforHiigalaxies, we plottedtheratioofcontinuumluminosityatX=4861 (see §4.1.1andabove).Foramoredirectcomparisonwith classes ofobjects.Theseresultssuggestthatthesourcecon- Á correctedforreddening,L(4861),totheinfraredluminos- the variousenergyregimesofstarformation(optical,infrared, the AGNmodelbecausewefeelthatrelationshipbetween LINERs, andSeyfertgalaxiesareallaboutthesame(—0.74, ity oftheobjectsinoursample.Usingthesenumbers,wefind and radio)isbetterunderstoodthaninAGNs.InFigure28, ing ratherthancomparingourresultswiththepredictionsof the resultsfromoursample.Wechoosethismethodofreason- Seyfert LIGsisnearlytwiceaslargeamongtheothertwo comparing thepredictionsofstarburstmodelwithsome termediate (pc-kpc)scalesbecomeavailable. dale etal.(1995)seemstosuggestotherwise,however.Anac- infrared luminosityoftheseobjects.TherecentworkLons- total radioluminosity.Consequently,theAGNsdetectedat based onradiodatasincetheenergyatthesewavelengthsactu- probably havetowaituntilmapsoftheradioemissiononin- pact-core AGNstothetotalenergybudgetofLIGswill curate determinationoftherelativecontributioncom- radio wavelengthsmaynotcontributesignificantlytothelarge pact coresdetectedbyLonsdaleetal.areonly~10%ofthe which islessobscuredthaninHnobjects(Lonsdaleetal. that ofHiiLIGs(§§2.1and2.9)isalsoinconsistentwiththe the AGNclass.ThehigherdustcontentofLINERsrelativeto therefore thatmanyoftheseobjectsshouldnotbeincludedin -0.82, and-0.70,respectively)butthatthescatteramong nosity ofthesegalaxies.Moreover,theluminositycom- ally representslessthan~10ofthetotalbolometriclumi- conclusions concerningthedominantenergysourceofLIGs hypothesis thattheLINERemissionisproducedbyanAGN tion thanHnobjects.Thisresultreinforcestheideadiscussed tection ofcompactradiocoresandtheiropticalclassification in §4.1.1thatthedominantsourceofionizationmany comes toaslightlydifferentconclusionwhenalloftheLINER improved classificationofthepresentpaper).However,one LINER LIGsisnotphotoionizationbyagenuineAGNand fert LIGshaveaslightlyhigherprobabilityofradio-coredetec- LIGs areexcludedfromtheirsample.Indeed,wefindthatSey- (this conclusionremainsquahtativelythesamewhenusing 10%-20%. Therefore,wefind thatupto50%ofthebolometric bol iv ir 0 1993). Inanycase,oneshouldbecautiouswhendrawing The importanceofstarburstsinLIGscanbeestimatedby 211 19 95ApJS. . .98. .171V 3 -1 1 don &Yin,arguethattheratio ofnonthermaltothermalradio phase ofsupernovaremnantsandthatitdependsverylittle duction ofrelativisticelectronsaftertheadiabatic(Sedov) where Listhenonthermalcomponentofradioluminos- flux isapproximatelythesame formostspiralgalaxies: formation ratesderivedfrom Haluminosities(eq.[2]).Con- on theuppermasslimitofIMF(incontrasttostar- ity. Notethatthissupernovaratetakesintoaccountthepro- (1990): Type IIsupernovarateusingtheprescriptionofCondon& Yin radio luminositiesofourobjectscanbeusedtoestimate the ies canbederivedfromtheradiodata.Ifweassumethatmost the SeyfertLIGsisprobablychangingvalueofthisratio of theradiationfromLIGsisduetoanuclearstarburst, the ence ofanadditional,nonstellarsourceenergyinsome among AGNLIGs,andespeciallySeyfertgalaxies.Thepres- these objectsisvariationsintheformofIMF(morespe- tial sourceofscatterintheHa-to-infraredluminosityratio from thenominalvalueforstarformation. and infraredluminositiesismuchweaker(ifatallpresent) Condon &Yin1990).Incontrast,thecorrelationbetweenHa cifically theIMFslope7andupperlowermasslimits; luminosities relatedtoreddeningcorrections.Anotherpoten- equality takesintoaccountthelargeuncertaintiesinHa L ofHIILIGscorrelateverywellwithmostthese get SFR(Ho)/SFR(IR)-\0L/L.In§2.3,wefoundthat have SFR(IR)^SFR(Ho:)1-500Myr,wherethefirst the lifetimeofstarswithM>10andthatinitialmass where theinfraredandHaluminositiesareinunitsof10L, objects havingL/=300-3000.Inthesegalaxies,wethus ( Salpeter1955).Furtherassumingthatßæ771inLIGs,we function (IMF)extendsupto—100Mwithslopey=2.35 and (2)assumethatthestar-formationrateisconstantover able Ho:emission(seealsoKennicutt1983).Equations(1) and rjisthefractionofionizingphotonsthatproduceobserv- ß isthefractionofbolometricluminosityradiatedbystars and Hunteretal.(1986),wehave duced bythestars,respectively.Thesetwoquantitiescanthere- thus decreasingthepercentageofbolometricluminosity tion or,insomeSeyfertLIGs,apower-lawAGNcontinuum, Using thederivationsofGallagher,Hunter,&Tutukov(1984) fore beusedtodeterminethestarformationratesingalaxies. ities aremeasuresofthetotalandionizingluminositypro- produced bythestarburst. the endof§2.11,however).Onotherhand,part the opticalcontinuumwouldincreasethisvalue(seenoteat optical continuummaybeproducedbyanoldstellarpopula- young stars.Underestimatesinthereddeningcorrectionsof NT Hair HaiT Q 0 0 lTHa Q 212 Another constraintonthestar-formationrateinthesegalax- In the“pure”starburstmodel,infraredandHaluminos- 24081 SNR =7.7X10-(ï//1Ghz)-Lyr-,(3) NT l1 SFR(Ha) =2700-LMyr-,(2) © American Astronomical Society • Provided by theNASA Astrophysics Data System VHaMQ 1 07 SFR(IR) =26/rL,Myr-(1) L/~ lOWlGHz)“-. (4) ir10 NTT VEILLEUX ETAL. -1 210 41 -1 -1 8 the linewidthsexpectedfrom gasmotioninthegravitational tive comparisonbetweenthewidth oftheobservedprofilesand an AGNemission-linespectrum. Unfortunately,aquantita- The majorityoftheobjectspresenting suchbroadprofileshave winds withtheambientmaterialofhostgalaxy. Norman &Ikeuchi1989)toarguethatthegasmotioninthese field ofthehostgalaxyisvery difficultbecauseweknowso have nuclear[Oin]\5007linewidthslargerthan600km s. dence thatviolentoutflowisalsopresentinatleastsomeof the literature (e.g.,Castor,McCray,&Weaver1975;et al. ber ofanalyticalandnumericalmodelspublishedin the wavelength dataontheirobjectswiththepredictionsofanum- objects inoursample.Nearly20%oftheLIGssample measurements fromourdata(see§2.6),thereisstrong evi- objects isregulatedbytheinteractionofsupemovae-driven Low &McCray1988;MacLow,McCray,Norman1989; ple showevidenceforviolentoutflows.Theycomparedmulti- become lessextremeifweonlyapplythestarburstmodelto massive stars(e.g.,Riekeetal.1993). H iiLIGsoriftheIMFisskewedtopreferentialformationof in studiesofthenuclearvelocityfieldtheseobjects.Thetime scales forgasdepletionandtherequiredmassesinOBstars numbers byfactorsof3-10.Thesemassesshouldbedetectable the interstellarmediumandassumingnolow-massstarsare Including thestarswithlowermasseswouldincreasethese mass inOBstarsof~10-10M©thenuclearregionalone. in oursample(lO^-lOergss“)wouldcorrespondtoatotal timescale isconsiderablyshorterthanthelifetimeestimatedby in thesesystems.Furthermore,theHaluminositiesobserved Carico etal.(1990)fromtherateofdetectiondoublenuclei axies wouldthereforebeonly10millionyearsorso.This formed. Inthispicture,theultraluminousphaseofthesegal- the entireinterstellarmediumintomassivestarsinabout4X The star-formationratederivedabovewillthereforetransform 1977; Chevalier&Clegg1985;Tomisaka&Ikeuchi1988;Mac luminosity withtheapproximateform the valuesderivedfrominfraredandHaluminosities. frared luminositytoHmassratioincreaseswiththeinfrared nosities. ResultsfromSandersetal.(1991)showthatthein- mation ratesderivedfromtheradio,infrared,andHalumi- culated aboveisthereforeofthesameordermagnitudeas The starformationratepredictedfromthesupernovacal- (using aSalpeterIMFwithanuppermasscutoffof100A/©). rate of10M©yrwouldproduceonesupernovaevery15 yr. Thisvalueofthesupernovarateisrelatedtostar- GHz) fortheobjectsinoursampletofindSNR0.005-1.0 son, Fall,&Freeman(1989)estimatedthatastar-formation formation ratethroughtheformofIMF.Forinstance,El- radio fluxestabulatedbyCondonetal.(1990,1991;?=1.49 Assuming thatthisratioalsoappliestoLIG,wecanusethe 10 yr,neglectingthemasslossofthesestarsbackinto 2 4.2. EvidenceforOutflowsinLuminousInfraredGalaxies In spiteofthelargeuncertaintiesaffectinglinewidth HAM90 havearguedthatmanyofthe14LIGsintheirsam- It isimportanttopointouttheimplicationsofstar-for- « IOL^uLoMö'.(5) Vol. 98 19 95ApJS. . .98. .171V -1 minosity ofLIGsisasubstantial fractionoftheirtotalbolo- strongly withtheinfraredluminosity ofthegalaxy(§§2.6and nuclear andcircumnuclear line widthsdonotcorrelate served inthemoreinfrared luminous objects(Fig.13),the complex opticaldeptheffects(Leechetal.1989;Keel1993). component. Note,however,thatthesmallernuclearreddening has beenejectedinaviolentoutfloweventalongwiththe gas possibility thatthedustinnuclearregionoftheseobjects 3.5). Thisresultissomewhat surprisingsincetheinfraredlu- can alsobeexplainedbydustdestructioninthenucleusor by files inafewoftheseobjects(§3.1)isalsoconsistentwith the ization isimportantoutsideofthenucleussomethese galaxies with[Om]X4363strongenoughtobemeasured out- objects (see§3.4).Finally,thepresenceofinverteddustpro- (§ 4.1.1).Thepositivetemperaturegradientfoundinthe two tended LINERemissionmightresultfromthisinteraction side ofthenucleusalsosupportspossibilitythatshock ion- or withtheslowmovinggasofapreviousoutflowevent;ex- is likelytointeractwiththeambientmaterialofhostgalaxy flows aremorelikely.Inanycase,theoutflowingcomponent cluded (e.g.,Axonetal.1989)althoughpoorlycollimatedout- et al.1994).Jet-inducedlinesplittingcannotbeformallyex- spatially resolvedhollowstructures(seealsoHAM90;Veilleux circumnuclear regionofsometheseobjectssuggeststhat most ofthelineemissionmaybeproducedby“walls” determining theexactgeometryofthisoutflow.Thedetection of emission-linesubstructures(densityenhancements)inthe complete two-dimensionalspatialcoveragepreventusfrom outward. Largeuncertaintiesinthelineprofilesandlackof of theline-emittinggasinthesegalaxiesisbeingaccelerated in thecircumnuclearregion.Theseresultssuggestthatsome which wecoulddeterminetheradialvariationsof[Om] tional motionintheLIGsofoursamplecomesfromlong- slit data.In§3.5,wefoundthatonly2ofthe12galaxiesin X5007 linewidthspresentbroaderprofilesinthenucleusthan teraction wasfoundinoursample(§2.10). broadening duetogalacticinteractionalsoappearsdoubtful worth 1983).Wealsoconsiderthispossibilityunlikelybased worth 1982;Dressier&Sandage1983;KormendyIlling- gradients inthenuclearregionofLIGswhicharenotobserved two gravitationaleffects:smearingoftherotationcurveacross since nocorrelationbetweenlinewidthsandthephaseofin- magnitudes ofthesegalaxies(e.g.,Soiferetal.1987).Line on thelate-typemorphologiesandfairlymodesttotalB- structure ofthegravitationalpotential:Kormendy&Illing- ( althoughthisvalueofMissomewhatdependentontheexact massive hostgalaxieswithM(bulge)^-22areneeded in normalspiralgalaxies(Rubinetal.1985;however,see larger than600kmswouldrequireextremelysteepvelocity the nuclearapertureorbroadeningeffectsrelatedto Bland-Hawthom, Wilson,&Tully1991).Inthesecondcase, nuclear stellarvelocitydispersion.Inthefirstcase,linewidths lations cannotbeusedtodeterminerigorouslytheimportance powerful toolsliketheFaber-JacksonandTully-Fisherre- optically selectedactivegalaxies(Whittle1989a,b;Veilleux of gravityrelativetonongravitationalforcesasinthecase very littleaboutthemassdistributionofLIGs.Consequently, No. 1,1995 1991a,b; Whittle1992a,b).Linewidthscanbeproducedby B jB Although broadnuclear[Om]lineprofilesaregenerallyob- Other, perhapsmoreconvincingevidencefornongravita- © American Astronomical Society • Provided by theNASA Astrophysics Data System LUMINOUS INFRAREDGALAXIES.II. 43-1 7-3 _1 -3 4123 5- 51 _1 -3 1 -1 nematic datapresentedheredonotwarrantsuchananalysis. luminous infraredgalaxiesofoursamplewouldthusrequire Seaquist 1988;Smith1993).Wefeelthatthefragmentary ki- using windflowmodels(e.g.,Schiano1985,1986;Duric & objects inoursample.Amorerigorousanalysisoftheultra- quence ofthemerger twolate-typespiralgalaxies a valuewhichprobablyonlyappliestothelowerluminosity find thatthisconditionissatisfiedwhendE/dt^\0ergss, unit Hmassislargerforthemoreluminousobjectsand the mates (Hc~0.5,P1-5fromHAM90,andn10),we ano 1985andKoo&McKee1992).Usingconservativeesti- ambient pressure,P/k,inunitsof10Kcm(seealsoSchi- where HisthescaleheightofgalaxyinkpcandP nuclear concentrationofmolecular gasisanaturalconse- Lamb, &Werner1988;Young etal.1986;Solomon&Sage more advancedmergersystems(Telescoetal.1988;Bushouse, centration ofthemoleculargasandinfraredluminosity per importance ofgalacticinteractionsinLIGs(seereferences in § 2.10).Previousstudieshavealsofoundthatthenuclearcon- that thebubblehasnot“blownout”ofhostgalaxy.There- et al.(1989),thefollowingconditionmustbefulfilled: fore, accordingtoMacLow&McCray(1988)and an AGN(seethediscussionofNGC3079byVeilleuxetal. line profilesmayrequireanadditionalsourceofenergysuchas Assuming typicalvaluesfortheradiusofexpandingbubble observed inmostofourobjects.LIGswithbroaderemission- 210 kms,whichareofthesameorderashalflinewidths of ~kpcand«^10cm,weobtainbubblevelocities~40- derive anenergyinjectionrateoforder~10-10ergss. and assumeanenergyoutputpersupernovaof~10ergsto the supernovaratederivedin§4.1.2(SNR^0.005-1.0yr) which isusedinpoweringtheoutflows.Thislastparameter starburst. InthecaseofHnLIGsoursample,wecanuse probably dependsonthenatureofenergysource:AGNor panding bubbles,orthefractionofbolometricluminosity the ambientmediumofgalaxies,size(age)ex- infrared luminositymayreflectvariationsinthepropertiesof Consequently, thelackofcorrelationbetweenlinewidthsand ( «oincm)accordingto 1991 ;Sanders1992).V-body simulationsshowthatsuchhigh 1988; Tinneyetal.1990;Sanders etal.1991;Scoville 2 kp70 kpc7 radius ofthebubble(Rinkpc)anddensitymedium (kinetic) energyinjectionrate(dE/dtinergss“)aswellthe panding intoaninfinitehomogeneousmedium(Weaveretal. the energypoweringoutflow.Anumberofparameters flow velocity,however.Inthecaseofawind-blownbubbleex- other thantheenergyinjectionratearedeterminingout- 1994). Note,however,thatthepreviouscalculationsassume metric luminosityandthereforeitshouldbeagoodmeasureof 0 1977), thevelocityofbubble(innkms)isrelatedto The resultsfromthepresentstudyemphasizeonceagain 423/2l D -3.0X\0-(dE/dt)H^Pïn<100,(7) 0 362l t; =3XlO-(dE/dt)R~nö.(6) 4.3. OriginandEvolution 213 19 95ApJS. . .98. .171V 78 8 9 jects inoursamplewhichpresentalargerdustcontentoutside the firstclassofobjects.These featuresindicatethattheoptical tion thanHngalaxies.(2)AnotherindicationthatAGNLIGs to underestimatetheactualdustcontentofthesegalaxies within themergingtime(10-10yr;Weedman1983;Quin- LIGs orisbeingswampedby ayoungerstarburst.Note,how- continuum ofAGNLIGsisproduced inpartbyanold(10- is thepresenceofstrongerMg ibandHßabsorptionfeaturesin may beatamoreadvancedstageofevolutionthanHnLIGs Although theopticalmethodusedinpresentstudyislikely the nucleusofSeyfertLIGsthaninHnobjects.Allthree ob- emission-line Balmerdecrementisobservedtobesmaller in into AGNs/QSOs:(1)Theamountofdustderivedfrom the tionary sequenceinwhichsomeoftheHnLIGsmayevolve is sufficientlyshorttoallowtherefuelingprocessoccur (Leech etal.1989;Keel1993),thisresultisconsistentwith of thenucleusthaninhaveAGNopticalspectra. lan &Shapiro1989,andreferencestherein). is veryuncertain;itremainstobeseenwhetherthistimescale cesses neededtofunnelgasdownintopreexistingMBH.Con- merger phase.Unfortunately,littleisknownontheexactpro- was formedbyagalaxyencounteratanearlierepoch.Tidal that theformationofMBHmayprecedepresentphase Seyfert LIGsbeingatamoreadvancedstageofdustdestruc- sequently, thetimescaleforrefuelingofapreexistingMBH sponsible forreactivatingtheseblackholesbeforethefinal forces inducedbythepresentgalaxyinteractionmaybere- tems foundin§2.10isindeedconsistentwiththeformationof nario doesnotexcludethepossibilitythatpreexistingMBH merger formationinatleastafewsystems.However,thissce- (e.g., NGC5256[Mrk266]and7592;§2.10)suggests other hand,thepresenceofAGNinlooselyinteractingsystems an activenucleusduringtheinfraredluminousphase.On wind, andpossibleradiojets(Begelman,McKee,&Shields rounding gasthroughitsintenseradiationfield,X-rayheated Weedman 1983;Spitzer1985,1987;Quinlan&Shapiro law 1973;Begelman&Rees1978;LightmanShapiro or tothefuelingofapreexistingblackhole(Spitzer1971;Sas- able totheformationofacentralmassiveblackhole(MBH) man &Scoville1988;Shlosman,Frank,Begelman1989). winds. If,ontheotherhand,gasconcentrationbecomes this gasconcentration.Starformation(notincludedintheN- to thecentralkpc-scaleregionofmerger.However,such triggers theformationofacentralbarwhich“funnels”gas In thesecircumstances,thephysicalconditionsbecomefavor- man, Blandford,&Rees1984;Lin,Pringle,1988;Nor- stability canleadtofurtherradialinflow(Toomre1964;Begel- large amountofmechanicalenergybysupemovaeandstellar disrupt thegasphaseofmergerthroughdepositiona the centralregionofmerger.Suchnuclearstarburstsmay body simulationslistedabove)isundoubtedlyimportantin quist 1991).Violenttidalforcesresultingfromtheinteraction sufficiently densetobeself-gravitating,fragmentationandin- models havedifficultiespredictingthesubsequentevolutionof (Negroponte &White1983;Noguchi1988;BamesHem- 214 10 yr)stellarpopulationwhich iseithernotpresentinHn 1983; Begelmanetal.1984). 1989). Anactivenucleusresults,furtherdisruptingthesur- A fewotherresultsfromthepresentstudysupportanevolu- The high-frequencyofAGNamongadvancedmergersys- © American Astronomical Society • Provided by theNASA Astrophysics Data System VEILLEUX ETAL. lengths. Ontheotherhand,it mayreflectrealphysicaldiffer- likely thattheSeyfertsignposts canbedetectedatopticalwave- with relativelylittlenucleardust aretheoneswhereitismore tion ofactivenuclei.Thismay beaselectioneffect:galaxies Low nucleardustcontenttherefore seemstofavorthedetec- trated towardthenucleus,inagreementwithoftenpeaky sion-line characteristics(oneSeyfertgalaxyandtwoLINERs ). are observedinonlythreeLIGs,allofwhichhaveAGNemis- distribution ofthemoleculargasinthesegalaxiesandtheir and Hnobjects.Thedustdistributiongenerallyisconcen- the faintX-raytailofopticallyselectedQSO. the nucleusappearslessdustythancircumnuclearregion LIGs isfoundtobeslightlylessreddenedthanthatofLINERs emission-line Balmerdecrement.ThenuclearregionofSeyfert rule outanoverlapoftheX-raypropertiestheseobjectswith possibilities. Thefaintupperlimitspresentlyavailableonthe keV) willprovideagoodtesttodifferentiatebetweenthesetwo AGN orWarmers.Observationsathighenergies(E^100 negative [Sn]densitygradients.Inverteddustprofilesinwhich hard X-rayfluxesofultraluminousinfraredgalaxiesdonotyet photoionization byaenergeticnuclearcontinuumfroman contrast, themostlikelyionizationprocessinSeyfertLIGsis rather thanphotoionizationbyagenuineactivenucleus.In red-selected galaxiesisproducedthroughshockionization the strengthsofstellarabsorptionfeatures,anddered- LIGs suggestthatmostoftheLINERemissionintheseinfra- pears tobeacommonfeatureofLIGs,regardlesstheir dened continuumcolors,circumnuclearstarburstactivityap- distance fromthenucleus.Basedonemission-lineratios, nuclear spectraltypes. the AGNincreasewithinfraredluminosity,reachingvaluesof on theotherhand,isrelativelyconstantat~27%. which hasoftenbeenneglectedinpreviousstudies.Wefind to determinethedominantionizationprocessinthesegalaxies. 62% and54%,respectively(Table3).ThefractionofLINERs, of LIGswithAGNspectraandthefractionSeyfertsamong The removaloftheseabsorptionfeaturesisadelicateprocess this studycanbesummarizedasfollows: from ouranalysisofthenuclearspectrathatbothfraction nostics correctedfortheunderlyingstellarabsorptionfeatures the propertiesofline-emittinggasandunderlyingstellar population inandoutofthenucleus.Themainconclusions surements onasubsampleof23thesegalaxiestoinvestigate sented inPaperI,werecombinedwithcircumnuclearmea- 200 luminousIRASgalaxies(LIGs).Thenucleardata,pre- does notnecessarilyreflectthestageofdustdestructionin good indicatorofthetimeintervalsincelaststarburstbut by agenuineAGN.Thestrengthoftheabsorptionfeaturesis nucleus. content thatanyotherclassesofLIGs,andmaynotbepowered characteristics. Theseobjectswerefoundtohavealargerdust ever, thatthiseffectisstrongeramongAGNLIGswithLINER 4. Thedustcontentofthesegalaxieswasestimatedusingthe 2. Theoriginofthelineemissionoftenisafunction 3. Theinfrared,radio,andopticalpropertiesofLINER We haveconductedaspectroscopicsurveyofsample 1. Itisimportanttousealargenumberofline-ratiodiag- 5. SUMMARY Vol. 98 19 95ApJS. . .98. .171V .1990,ApJ,364,471(AHM90) to studythegasdynamicsintheseobjects.Therelativelylow Boksenberg, A.,Carswell,R.F.,Allen, D.A.,Fosbury,R.A.E.,Pension, Bland-Hawthom, J.,Wilson,A.S., &Tully,R.B.1991,ApJ,371,LI9 Bland, J.,&Tully,R.B.1988,Nature, 334,43 Binette, L.,Dopita,M.A.,&Tuohy, I.R.1985,ApJ,297,476 Bica, E.,Alloin,E>.,&Schmidt,A.1990,MNRAS,242,241 Begelman, M.C,&Rees,J.1978,MNRAS,185,847 Begelman, M.C,Blandford,R.D.,&Rees,J.1984,Rev.Mod.Phys., Baldwin, J.A.,Phillips,M.M.,&Lerievich,R.1981,PASP,93,5(BPT81 ) Axon, D.J.,etal.1989,Nature,341,631 Axon, D.J.,&Taylor,K.1978,Nature,274,37 Ashby, M.,Houck,J.R.,&Hacking,P.B.1992,AJ,104,980 Annus, L.,Heckman,T.M.,&Miley,G.K.1989,ApJ,347, 727 Allen, D.A.,Norris,R.P.,Meadows,V.S.,&Roche,P.F.1991,MNRAS, spectral resolutionofourdatapreventedusfromstudyingthe ing perhapsthatthemassiveblackholewhichispresumedto tivity precedesthefinalmergerphaseofinteraction,imply- the dominantnuclearsourceofionization.Inatleasttwocases termine whetherthelargefractionofAGNsamongadvanced Binette, L.1985,A&A,143,334 Begelman, M.C,McKee,C.F.,&Shields,G.A.1983,ApJ,271,70 Barnes, J.E.,&Hemquist,L.E.1991,ApJ,370,L65 Balzano, V.A.1983,ApJ,268,602 Allen, D.A.,Roche,P.F.,&Norris,R.1985,MNRAS,213,67P gering theluminousinfraredemissionandperhapsalso (NGC 5256=Mrk266andNGC7592),however,Seyfertac- and thosewithAGNspectraarefoundmorefrequentlyinad- determining theextentofthiscontinuumsource. tamination bythecircumnuclearstarburstpreventsusfrom mergers isaluminosityeffectratherthananrelatedto vanced mergers.Thesizeofoursampleisnotsufficienttode- the HßandMgibabsorptionfeaturessuggestexistenceof AGN emission-linesignaturesdonot.Theradialvariationsof has beenreactivatedbythepresentinteraction. nuclear activityinthesegalaxies:theultraluminousobjects nearly allLIGs,regardlessoftheirnuclearspectraltypes.Con- a strongsourceoffeaturelesscontinuuminthenucleus reflect thefactthatstellaroutputofgalaxieswithpowerful into AGNLIGs.Ontheotherhand,thisresultmaysimply evolutionary scenarioinwhichsomeoftheHnLIGsevolve older thanthatofHnLIGs.Thisresultisconsistentwiththe exist intheseobjectswasformedapreviousencounterand HII regionsshowsevidenceforyoungstars,whilegalaxieswith features indicatethatthestellarpopulationcharacterizing nuclei ofAGNs(andespeciallytheLINERs)isonaverage (e.g., Goldaderetal.1995;Veilleux,Sanders,&Kim destruction/expulsion thanHnLIGs.Finally,complexopti- Hines 1991;&Wills1993). useful toevaluatetheimportanceoftheseopticaldeptheffects spectroscopy andspectropolarimetryoftheseobjectswouldbe ing asmalleramountofdustinthenucleus.Long-slitinfrared cal deptheffectsmayalsoexplaintheseresultswithoutinvok- enees betweentheseclassesofobjects:galaxieswithSeyfert emission linesmaybeatamoreadvancedstageofdust No. 1,1995 M. 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