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1988AJ 95. . 35 6C CORE 26 1 1l 1 n12 12 THE ASTRONOMICALJOURNAL THE IRASBRIGHTGALAXYSAMPLE.III.1-10OBSERVATIONSANDCOADDEDDATA ¡im observations,aswellcoaddedIRASdata,of61galax- bolometric luminosity, 3.83X10W. be importantininfraredgalaxies(BecklinandWynn-Wil- appear tobethemostnumerousobjectsknown(PaperI). ies, and,atthehighestinfraredluminosities,IRASgalaxies parable toorgreaterthanthatofstarburstSeyfertgalax- local universe.ThespacedensityofIRASgalaxiesiscom- portance ofinfraredemissionintheenergybudget properties oftheBrightGalaxySample.Theresults1-10 emergence ofactivenucleioccurs. These resultssuggestthattheluminosityrange phase intheformationofquasars(Sandersetal.1988). liams 1987;Hill,Wynn-Williams,andBecklin tive nuclei(see,forexample,Ealesetal,1988;Carico frared luminositygalaxies(L^10Lq;Lisdefinedin emission inthevastmajorityoflowtomoderatelyhighin- of greatimportance. Understanding thenatureofthisinfraredemissionisclearly after referredtoasPaperI)hashelpeddemonstratetheim- * Throughoutthetext,Histakenas 75 kmsMpc;Listhesolar ies fromtheBrightGalaxySamplearepresented.Allof of themostextremeluminosities-known. Bycomparingthe Sanders etal.1988),andthatsuchgalaxiesmayrepresenta Sec. Ill)isduetostar-formationprocesses,ratherthanac- galaxies inthecurrentsample with galaxiesofbothlower 61 galaxieshaveL>10;thus,theyarerepresentative 10L 10Liscorrelatedwithincreasedemissionfromhotdustcharacteristictemperatures bands havebeenobtained.Itisfoundthatanincreaseinthetotalinfraredluminosityabove increasing luminosity,thetemperatureofwarmercomponentisindependentluminosity.Thef with asingledusttemperature,butrequirescold(T—30-50K)componentcoupledwarmer measured at1.3,1.6,2.2,3.7,and10/¿m.Inaddition,coaddedIRASmeasurementsallfour objects, indicatingthattheradiationat12and25jumisdominatedbyemissionfromlargedustgrains appears to“turnon”atluminositiesofroughly10L.Thefar-infraredemissioncannotbemodeled Galaxies fromtheIRASBrightGalaxySamplewithinfraredluminositiesZ,>10Lhavebeen indicates asubstantialextendedcomponentformostofthegalaxiesinthissample,implyingthatstar- radiating athightemperatures,ratherthanPAHs.Thespatialdistributionofthe10jumemission consistent withacontributionof50%ormorefromcentralpointsource. exponential scalesizescharacteristicofcompactsources,andhalfthegalaxieshave10jumemission formation processescontributesignificantlytotheluminosities.However,one-thirdofgalaxieshave 0 (T^10 K)component.Althoughtherelativecontributionfromcoldcomponentdecreaseswith — 800Kcontributingasubstantialfractionofthe2.2and3.7fimemission.Thishotdustemission ( 12/j,m)/f(25jum)ratiosforthegalaxiesinthissamplearesmallcomparedwithotherextragalactic v 0 IR0 v I. introduction Palomar Observatory,CaliforniaInstituteofTechnology,Pasadena,91125 n FOR GALAXIESWITHL>10 IR Received 25August1987;revised27October1987 VOLUME 95,NUMBER2 ABSTRACT 12 1 12 12 n Lir>10 L,andinparticulartodeterminewhetherthe the extremepropertiesreportedforgalaxieswith the natureoftransitionfromnormalgalaxypropertiesto luminosity (L<10andthehighestluminosities to alesserdegree,ininfraredgalaxiesatlowerluminosities. unusual propertiesofgalaxieswithL>10arefound, IRAS BrightGalaxySample(PaperI),whichcontains324 <5> —20°for14-24hr(PaperI). galaxies, andrepresentsallextragalacticobjectswithIRAS nation <5>—30°for0-12hr,15°12-14and 0 based onthefar-infraredluminosityL,whichistabulated in PaperIfortheBrightGalaxySample,andwhichutilizes 60 jamfluxdensitiesgreaterthan5.4Jyinanareaof (L £10L),itistheintentofthisworktoinvestigate luminosity between40and400jum(seeAppendixBofCata- the IRAS60and100jumdatatoobtainanestimateof IR loged GalaxiesandQuasarsObservedintheIRASSurvey IR0 galaxies, alistwascompiledofallgalaxiesfromtheBright nous brightgalaxies,orLBGs;theyaretabulatedinTableI, which thereare69,willhereafterbereferredtoasthelumi- Galaxy SamplewithL>10.Thesegalaxies,of along withtheircoordinatesand redshifts,reprintedfrom —14 500sq.deg,withGalacticlatitude|6|>30°,anddecli- Palomar ObservatorySkySurvey prints.Ofthese69galax- Paper I,andtheiropticaldiameters asmeasuredfromthe FIR ies, eightwerenotobservableat thetimePalomarobser- irq lyzed inthispaper,therefore represent anunbiasedand (1985)). Inordertofocusonthemostluminousinfrared nearly completesampleofluminous infraredgalaxies. vations werebeingdone.The remaining 61galaxies,ana- FIR0 The galaxiesanalyzedinthispaperareasubsetofthe The selectionofgalaxiesforinclusioninthisanalysiswas II. THESAMPLE Metadata, citationandsimilarpapersatcore.ac.uk FEBRUARY 1988 1988AJ 95. . 35 6C 357 CARICOETAL.:IRASGALAXIES © American Astronomical Society • Provided by the NASA Astrophysics Data System IC 1623 NGC 34 in ZW0351 IRAS 0136-10t MCG-02-01-051 MCG-03-04-014 NGC 232t MCG+02-04-025 IRAS 0243+213 NGC 958 NGC 695 IRAS 0335+15 UGC 2238 UGC 2369 NGC 1143/4 IRAS 0518-25 UGC 2982 IRAS 1211+03 MCG-03-12-002 ZW 247.020 IRAS 1434-14 IRAS 1222-06 NGC 3690 A1101+41 IRAS 1056+24 IRAS 1017+08 IC 563/4t IRAS 0857+39 NGC 1614 NGC 533it UGC 8739 Mrk 273 NGC 5257/8 NGC 5256 NGC 5104 IC 860 NGC 4418 UGC 6436 MCG+00-29-023 UGC 4881 NGC 2623 UGC 8335 MCG+01-33-036t NGC 4922 Mrk 231 M CG+08-23-097 NGC 3110 MGC+08-18-012t UGC 5101 UGC 8387t NAME Arp 256 VV114 Mrk 938 UGC 1315 Arp 243 UGC 2388 IC 2810 Mrk 617 Arp 193 Arp 55 Mrk 1490 UGC 8696 UGC 8641 UGC 8632 Mrk 171 VV 253 UGC 8391 VH Zw506 UGC 7545 V32 UGC 8135 UGC 8058 OTHER NAME (h)(m)(s)(deg)(arcm)s) 14 13 13 13 13 13 13 12 12 11 11 11 11 14 13 13 12 12 12 12 12 10 10 10 13 0 0 0 2 2 2 4 3 2 4 2 1 1 1 5 4 1 1 1 9 9 9 9 8 8 Table I.Identificationofgalaxies. RA 40 36 43 28 48 41 43 35 52 51 16 31 17 47 42 36 25 23 35 34 49 37 48 24 22 56 57 54 43 33 32 59 59 19 11 18 18 17 18 18 17 12 13 12 5 7 8 9 1 1 33.4 48.0 42.0 28.1 24.0 22.8 38.6 49.2 33.4 57.1 18.0 43.2 18.0 17.5 41.3 51.6 49.2 42.0 35.8 11.8 52.3 53.8 22.1 41.3 29.0 38.6 35.5 58.6 40.1 22.1 22.1 32.2 44.2 39.6 25.2 15.6 21.4 14.2 12.2 19.0 17.8 18.5 13.0 9.8 5.8 6.5 4.8 4.6 1.7 1.0 -1950- -12 -17 -23 -10 -17 - 3 -10 - 0 +22 +14 +16 +21 +12 -18 +14 -14 - 0 - 6 - 2 - 6 -25 - 8 + 5 +15 +49 + 2 +35 +56 +58 +14 + 1 +48 + 0 +34 + 3 +41 +24 +25 +62 +24 + 4 +57 +48 + 8 + 3 +61 +39 +29 +48 +44 DEC 39 23 42 46 50 20 51 53 46 22 23 23 25 55 47 30 31 36 50 56 42 55 24 40 27 21 23 23 52 36 34 36 24 48 28 41 34 32 14 15 12 17 7 9 5 5 5 7 8 8 25 53 37 44 32 14 10 48 52 49 53 36 48 40 55 10 10 24 54 20 43 41 37 40 52 59 38 26 53 20 12 14 13 13 14 17 14 14 17 18 7 2 6 6 1 7 1 4 2 8 3 RED SHIFTDS 0.0198 0.0250 0.0185 0.0208 0.0475 0.0311 0.0335 0.0208 0.0192 0.0326 0.0274 0.0353 0.0285 0.0312 0.0227 0.0177 0.0158 0.0316 0.0811 0.0260 0.0332 0.0171 0.0723 0.0105 0.0341 0.0241 0.0345 0.0185 0.0424 0.0380 0.0227 0.0276 0.0186 0.0229 0.0312 0.0250 0.0417 0.0480 0.0400 0.0399 0.0583 0.0129 0.0362 0.0245 0.0421 0.0294 0.0068 0.0161 0.0203 0.0260 (z) (arc s) 100 110 115 35 40 35 25 40 35 20 25 40 20 35 35 20 65 15 40 70 50 20 20 25 35 50 30 45 30 25 20 35 25 30 30 35 20 30 35 60 80 60 60 15 15 15 10 15 10 357 1988AJ 95. . 35 6C / /70focusoftheHale5mtelescopeatPalomarObservatory, ¡um, À/l=0.410.64and4.7re- ¡im (J),1.65/¿m(#),and2.23/¿m(A^);58wereobservedat beam position,theuncertainties intheratiosareconsider- ably lessthanthoseintheindividual fluxdensities.Forthe flux-density ratios(colors)are relativelyindependentof maximum emissioninthegalaxy. Sincethenear-infrared ficulties inaccuratelycentering inthebeampositionof photometric uncertaintiesforthe1.3,1.6,and2.2jummea- measuring fluxesatthatlocationallwavelengths.The taneous signalwasalwayslargeenoughtodothis),then position ofmaximumfluxat2.2¡uminthebeam(theinstan- surements aregenerally<8%, and areprimarilyduetodif- standard starsthatareeffectivelyonthesystemofTokunaga 3.7 and10/xmmeasurements, thephotometric uncertainties the 10.6jummeasurementswerecalibratedat10.1/xm,using were calibratedusingstandardstarsfromEliasetal.(1982); band widthsofthefiltersusedareA/l=0.24¡um,À/l0.30 spectively. Themeasurementsbetween1.27and3.69¡um 358 CARICOETAL.:IRASGALAXIES bolometer forthe10¿¿mmeasurements.Beamsizesranged south ofthegalaxy.Sixty-onegalaxieswereobservedat1.27 achieved bychoppingtoreferencepositions15"northand from 4.6"to10"indiameter,andskysubtractionwas 3.69 ¡Ltm(L');and59wereobservedat10.6/xm(N).The using asolid-nitrogen-cooledInSbdetectorsystemforthe (1984). 1.3-3.7 fimmeasurements,andahelium-cooledgermanium In general,observationsweremadebyfirstlocatingthe The 1-10fimmeasurementsweremadeattheCassegrain © American Astronomical Society • Provided by the NASA Astrophysics Data System b a Distheopticaldiameter,asestimatedfromPalomarObservatorySkySurveyprints. Paper I. RedshiftsarereprintedfromPaperI,andtakenaseitherv/corDH/cwherevDisgiveninTable1 0 0 IRAS 1713+53 IRAS 1533-05 IRAS 1525+36 IZW 107 ZW 049.057 IRAS 2249-18 Arp 220 ZW 475.056 ZW 453.062 MCG+01-42-088 NGC 6090 UGC 9618 MCG-03-57-017 NGC 6285/6 NGC 7771 NGC 7469 Mrk 331 NGC 7674 NGC 7592 HI. OBSERVATIONSANDDATAREDUCTION NAME Arp 293 Arp 302 Mrk 848 UGC 9913 UGC 12332 UGC 10267 UGC 12608 Mrk 928 OTHER NAME (h) (m)(s)(deg)(arcm)s) 23 22 22 23 23 23 23 23 23 15 17 16 16 16 15 15 15 15 14 RA 54 57 48 49 28 28 33 32 25 48 25 16 10 13 10 15 13 0 2 Table I.(continued) 47.8 44.9 27.4 32.4 45.6 52.1 44.6 42.7 24.0 46.3 47.5 31.2 52.8 24.7 28.1 14.2 19.0 3.1 9.6 -1950- - 5 -18 -19 - 4 + 4 +36 +42 + 7 +24 +53 +59 +52 +23 +19 +25 + 8 +20 + 8 +19 because alargefractionofthegalaxiesinthissampleare however, theuncertaintiesin10/xmdataarelarge density foreachgalaxytoobtaintheKcorrection.Also,this polated fluxdensitywasaveragedwiththemeasured centric velocity.Thisprocesssystematicallyoverestimates densities toestimatebyinterpolationthefluxat have beenmadeforeachgalaxybyusingthemeasuredflux have beenmadeforextinctionwithinourowngalaxy.Fur- where Galacticextinctionisgenerallysmall,nocorrections at 10/xmwouldbeinappropriate.SincetheBrightGalaxy enough, andtheredshiftssmallthatanycorrection process doesnotprovidecorrectionsforthe10/xmdata; the fluxdensitiesat3.7/xm,sothatwavelengthinter- filter wavelengthsforanequivalentgalaxywithzerohelio- Hence, individualcorrectionsforredshift(Kcorrections) at longerinfraredwavelengths. are typically^15%and20%,respectively,butrangeupto thermore, nocorrectionwasmadeforinternalextinction, mate. highly disturbed,andcorrectionswouldbedifficulttoesti- Sample wasdefinedtohaveGalacticlatitude|¿>|>30°, IRAS data(wheretypicalbeam sizeswere1.5'X4.75'),an 50% forsomesourcesduetotheincreasedbackgroundnoise were takenoneachnucleus.These individualmeasurements multiple nuclei.Insuchcases, near-infrared measurements ratios; however,whencomparing a10/xmfluxdensityto have beenusedincalculatingthe near-infraredflux-density individual flux densities fromallmeasuredpositions, has estimate ofthetotal10/xmemission, obtainedbyaddingthe The LBGshaveabroadrangeofenergydistributions. A largenumberoftheLBGscontainopticallyobvious DEC 35 40 55 48 49 41 36 24 30 11 13 17 13 16 18 16 9 0 8 24 59 41 43 52 40 58 20 31 55 22 48 55 20 18 14 0 6 8 a REDSHIFT DS 0.0507 0.0187 0.0236 0.0291 0.0260 0.0182 0.0534 0.0401 0.0118 0.0337 0.0242 0.0145 0.0165 0.0760 0.0180 0.0289 0.0244 0.0274 0.0246 (z) (arc s) 110 40 20 40 40 20 40 50 80 45 50 20 50 25 40 35 30 40 65 358 1988AJ 95. . 35 6C 1 f (1.65/zm)andR(2.2/1.6)=/2.3/zm)//^m) v luminosity Lforthosegalaxies hasbeentakenasL able forthelower-luminosity galaxies,theinfrared fine thelattersample.Since12and 25/zmdataarenotavail- ies andtheLBGsampleisluminositycutoffusedtode- by thehigherflux-densitylimitascomparedtolower- rithms oftheflux-densityratiosR(1.3/1.6)=/1.27/zm)/ bands. Theresultingluminosity,whichwillbeusedthrough- given above;L/isnot correlated withLforthe in theselectioncriteriabetweenlower-luminositygalax- luminosity sample),andhencetheonlyrelevantdifference where f(A)isthefluxdensityatwavelengthA.Throughout versus luminosityforabroadrangeofluminosities, sion onluminosityforinfraredgalaxiesbyplottingtheloga- luminosity between8and1000/zm,utilizingallfourIRAS ate fluxdensityratio.Thelower-luminositydata(¿ this paper,thenotationR(Â/Â)willrefertoappropri- ¿fir; thesamplemeananddispersionofL/^for out therestofthispaper,providesabetterestimate using themethodofPeraultetal.(1987)toestimateL, quent analysestheluminositywasadjustedforeachgalaxy LBGs. ThedashedlinesinFig. 1,atlog[A(1.3/1.6)] LBG sample.Thetwosampleshavethesamemeanredshift Soifer etal.1984)thatwasflux-densitylimitedat0.5Jyand sample ofIRASgalaxies(theMinisurveySample;see luminosities L. Source Catalog.Forcompleteness,thisprocedurewasap- 60/zm, afactorof10fainterthanthelimitusedtodefine flux-density ratiosusedintheanalysis,aswellinfrared Table II,andtheA'correctednear-infraredfluxdensitiesare given inTableIII.IVliststhenear-infraredandIRAS well asthenear-infraredbeamdiameters,aretabulatedin total infraredluminosityandissystematicallyhigherthan Point SourceCatalog(1985)forthe12/zmfluxdensity.The far-infrared luminosity,L(seeSec.II),forallsubse- tions fromthedatainPaperIat60and100fimaresmall. plied toallfourIRASbands,althoughtheresultingdevia- LBGs is1.30±0.14. which isbelowthesensitivitylimit(0.5Jy)ofPoint minimize thisproblem,aneffortwasmadetouseflux-den- ded, providingflux-densityestimatesdownto~0.4Jy, original IRASscansoverthegalaxieswerethereforecoad- vidual objects. luminosity isdistributedroughlyequallybetweentheindi- throughout thepaper,anditisassumedthatinfrared that bothsetsofnear-infraredmeasurementshavebeenused near-infrared emissionwasclearlydominant.However,for measurements becauseofthedifferenceinbeamsizes.To when attemptingtorelatethenear-infraredratiosIRAS been used.Forallofthegalaxiesthereisclearlyaproblem sity ratiosfromonlythatpositionwithineachsourcewhose (the systematicallyhigherluminosityoftheLBGsisoffset IR IR v IRF IR v IR l2 lK¥l IR IR 359 CARICOETAL.:IRASGALAXIES 11 oftheLBGs,nosuchdominantpositionwasfound,so < 10Z,q)arefromCaricoetal.(1986),andrepresenta FIR = 1.3xL,adoptingthemean L/fortheLBGs fir IRFIR a) 1.3-3.7jumMeasurements:TheSourceoftheNear- Figure 1showsthedependenceofnear-infraredemis- The observednear-infraredandIRASfluxdensities,as Although theLBGsamplewasselectedonbasisof Many oftheLBGshaveonlylimitslistedinIRAS © American Astronomical Society • Provided by the NASA Astrophysics Data System Infrared Emission IV. DISCUSSION 12 1 1 1 /zm measurements,itmayproveextremelyuseful,particu- A(2.2/1.6), whereastheobservedrangeinA(3.7/1.6)is er wavelengths.Furthermore,theLBGswithL>10 parently affectsthenear-infraredflux-densityratiosatlong- dicating thattheincreaseinluminositybeyondlO!^ap- indicates thatA(3.7/1.6)iscorrelatedwith(2.2/1.6),in- A (1.3/1.6)forL£10L.Further,Fig.1(b)suggests nosities oftheLBGsarealsoreflectedinnear-infrared ratios appropriatefornormalspiralgalaxies(Aaronson the A(3.7/1.6)ratio. sample, indicatingasignificantluminositydependenceof all haveA(3.7/1.6)ratiosthatareamongthelargestin available forthelower-luminositygalaxies.However,Fig.2 not includedinFig.1,since3.7/zmmeasurementsare almost fourtimesthatinA(2.2/1.6).The3.7/zmdatawere uncertainties inthemeasurementsisroughlytwicethat are plottedonthex,y,andzaxes,respectively,ofastandard figure isathree-dimensionalrepresentation,wheretheratios evidenced bythelargerchangeinA(2.2/1.6)comparedto from normalgalaxycolorswithincreasingwavelength,as emission. Thenear-infraredflux-densityratiosdeviatemore burst galaxyNGC253.The1.2-2.2/zmmeasurementsfor burst nucleusarethoseofthearchetypalstar- The flux-densityratiosusedforanAGNarethoseofthe normal galaxyemission(N),a“starburst”nucleus(B),and ties inthe3.7/zmdata;dispersionA(3.7/1.6)dueto not beattributedentirelytothelargerstatisticaluncertain- scale usedfortheA(3.7/1.6)axisinFig.2).Thiseffectcan- properties oftheLBGsislargestat3.7/zm(notedifferent is alsoshown. the apparentpositionofdatainthisthree-dimensional right-handed coordinatesystem.Toeliminateambiguitiesin tra moredifficulttoobtain. ment) isfromBecklin,Fomalont, andNeugebauer(1973). like energysource.Theflux-densityratiosusedforastar- this paperthetermAGNwillreferspecificallytoaquasar- quasar 3C273(fromNeugebaueretal.1987);throughout normal galaxyistakentobe0.43(Lawrenceetal.1985). an activegalacticnucleus,orAGN(A).A(3.7/1.6)fora space, theprojectionofdataontoeachaxisplanes large amountsofvisualextinction,makingtheopticalspec- larly sincesuchinfrared-luminousgalaxiesgenerallyhave that themechanismsaffectingnear-infraredemission tios ofmosttheLBGslieroughly betweentheratiosex- tic sources.Itisseenthatthenear-infrared flux-densityra- continuum emissionoftheLBGs tothatofotherextragalac- density (takentobeequalthepublished3.5/zmmeasure- NGC 253arefromScovilleetal.(1985),andthe3.7/zmflux As thisprocedurewouldrequireonlybroadband1.6and2.2 ally infrared-luminousgalaxiesfrommorenormalobjects. pected fornormalgalaxiesandthose ofactivenuclei,andare cutoff, oneshouldbeable,onaverage,toseparateoutunusu- infrared emissionalone.ByusingA(2.2/1.6)~l a meansofselectinghighlyluminousgalaxiesbasedonnear- “turn on”atluminositiesofroughly10Z,.Thisindicates 1977). IR0 1.6), andA(3.7/1.6)fortheLBGsareshowninFig.2.This IR0 (log [A(2.2/1.6)]~0or[#—A]~0.5mag)asarough 0 = —0.09andlog[A(2.2/1.6)]—0.12,representthe From Fig.1itisclearthattheextreme8-1000/zmlumi- Figure 2showsthatthedispersioninnear-infrared The near-infraredflux-densityratiosA(1.3/1.6),(2.2/ Included inFig.2arerepresentativeflux-densityratiosfor Figure 2presentsadirectcomparison ofthenear-infrared 359 1988AJ 95. . 35 6C 360 CARICOETAL.:IRASGALAXIES © American Astronomical Society • A1101+41 IRAS 1056+24 IRAS 1017+08t NGC 3690t UGC 6436 MCG+00-29-023 NGC 3110 UGC 5101 UGC 4881 IRAS 0857+391 IRAS 0518-25 NGC 2623 NGC 1614 MCG-03-12-0021 IRAS 0335+15t UGC 2982 IRAS 0243-1-213 NGC 1143/41 UGC 2369t NGC 695 MCG+02-04-025t MCG-03-04-014 IC 1623t UGC 2238 NGC 958 MCG-02-01-051 NGC 34 NAME a CODE OBS (b) (b) (c) (a) (b) (a) (a) (d) (b) (c) (b) (a) (b) (a) (d) (a) (b) (c) (b) (a) (b) (a) (a) (b) (b) (b) (d) (b) (a) (a) (c) (c) (a) (a) b (arc sec) BEAM 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 5.0 5.0 5.0 5.0 7.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 1.3 fim 22.81 12.42 17.30 11.12 17.62 11.12 12.89 42.28 34.21 14.39 12.89 11.86 17.46 23.02 11.64 13.00 10.62 12.77 11.54 15.78 16.52 5.78 5.57 5.42 3.27 4.35 8.59 0.91 9.33 4.55 1.61 1.80 1.41 6.83 6.40 8.13 2.46 4.35 5.08 8.67 8.91 7.76 6.40 8.67 8.06 5.94 1.53 Table II.Observedfluxdensities. 1.6 2.2fim3.7/mi 32.92 20.96 24.07 20.02 15.76 16.50 29.75 15.76 13.60 27.38 59.90 48.47 15.05 27.89 16.35 24.52 35.44 13.35 17.92 14.24 17.44 16.96 15.19 10.70 12.29 14.50 18.43 14.50 4.18 7.97 7.90 8.12 6.51 2.38 2.47 9.58 1.97 1.44 6.75 8.19 3.17 5.77 7.47 9.41 8.50 8.66 1.88 Provided bythe NASA Astrophysics Data System c PALOMAR (mJy). 38.21 24.79 25.25 27.43 22.82 14.66 16.99 55.75 10.82 52.75 14.53 59.46 49.00 18.12 28.99 27.18 15.21 37.17 13.37 16.68 16.38 13.75 15.07 14.13 10.82 14.94 16.68 16.53 7.84 8.36 3.86 4.47 4.77 4.35 6.58 3.68 9.51 7.08 9.00 2.57 5.84 7.28 8.52 8.06 8.59 8.36 1.52 <30.46 123.50 122.37 32.48 31.60 20.88 80.11 31.02 30.46 43.62 37.64 40.52 39.78 18.35 11.90 63.05 51.01 13.54 31.89 44.84 10.37 11.69 14.05 10.66 12.70 13.54 11.58 9.20 3.87 2.88 4.24 5.44 30.49 5.80 27.300.270.56 7.58 9.54 4.44 3.50 6.60 9.03 5.24 1.66 <51.55 483.28 273.02 <34.69 <31.64 <32.23 <31.64 895.78 <31.35 288.54 207.11 515.47 122.52 182.05 136.84 832.15 160.03 251.31 128.29 113.82 158.56 150.04 122.52 10 fim 34.37 80.95 61.97 28.85 10.48 69.22 39.83 57.04 52.99 89.58 83.21 c <0.16 IRAS(Jy) 12 fim2560 4.75 0.20 0.34 0.23 0.26 0.64 0.25 0.17 0.35 0.34 0.76 0.60 1.57 0.14 0.39 0.76 0.49 0.32 0.39 0.80 0.26 0.51 0.25 0.36 0.3 28.71 0.81 0.79 0.47 0.68 2.16 1.44 1.35 1.31 3.52 1.05 8.24 0.80 1.73 0.66 0.76 4.18 0.69 0.97 2.15 1.19 1.63 1.02 1.67 1.51 1.43 112.13 12.09 11.32 12.09 23.52 30.40 13.94 22.65 10.27 17.85 5.70 5.53 5.56 6.67 5.99 7.53 5.52 10.52 5.80 5.19 7.86 5.71 5.49 8.35 5.55 7.75 6.68 8.5 127.82 100 fim 23.03 20.07 11.00 10.03 11.63 17.99 28.66 10.65 37.67 11.68 34.08 12.80 10.78 11.49 12.38 16.69 14.83 10.21 16.10 6.29 4.59 7.56 7.07 18.6 16.6 360 1988AJ 95. . 35 6C 361 © American Astronomical Society • Provided by the NASA Astrophysics Data System ZW 247.020 IC 860 I ZW107 ZW 049.057 IRAS 1434-14 NGC 5257/8t NGC 5256t NGC 5104 IRAS 1222-06 IRAS 1211+03 IRAS 1533-05 Arp 220 IRAS 1525+36 UGC 8739 Mrk 273 UGC 8335t UGC 9618 NGC 4922t Mrk 231 NGC 4418 NGC 6090t MCG+08-23-097 ZW 475.056 NGC 6285/6 MCG+01-42-088 ZW 453.062 IRAS 1713+531 Mrk 331 NGC 7771 NGC 7674 NGC 7469 IRAS 2249-18 MCG-03-57-017 NGC 7592t CARICO ETAL.:IRASGALAXIES NAME a CODE OBS (b) (a) (b) (b) (b) (b) (c) (a) (a) (b) (b) (a) (a) (c) (a) (a) (b) (b) (a) (a) 5 (arc sec) BEAM* 10.0 10.0 10.0 10.0 10.0 10.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 1.3 fitn 48.54 45.51 14.13 13.00 16.22 10.72 25.95 52.25 10.92 18.80 17.62 17.79 12.19 10.14 4.64 7.55 7.62 5.04 6.22 4.23 4.64 5.13 9.16 7.62 7.48 3.33 7.55 2.92 5.62 8.59 8.13 6.76 6.70 8.44 9.96 5.57 1.80 5.84 2.14 6.11 6.34 2.02 1.61 c _i(A), PALOMAR(mjy). v Table II.(continued) 100.33 101.26 1.6 fim2.23.7/im 21.95 30.58 11.41 28.15 36.43 11.31 14.11 27.63 12.40 12.99 10.60 19.84 11.21 16.65 13.23 17.44 12.06 81.18 16.05 16.50 17.60 15.61 9.94 4.46 2.76 9.58 9.76 6.39 6.16 5.77 3.89 7.47 2.41 8.35 6.88 9.07 8.42 2.59 2.76 8.19 8.66 189.77 182.91 109.20 21.99 33.90 21.79 30.08 11.54 34.85 12.31 15.93 12.31 28.20 12.08 11.33 15.21 11.23 24.79 15.50 14.26 16.08 14.80 19.69 16.68 8.59 9.34 3.24 7.15 5.89 6.23 3.62 9.00 3.18 3.89 8.75 5.18 8.06 2.69 8.92 8.06 2.46 8.59 8.75 379.90 343.30 156.92 <6.08 <2.21 21.07 24.64 21.86 11.16 17.69 29.09 15.84 21.27 59.11 10.27 16.74 11.58 12.93 <183.74 12.35 18.69 10.46 17.21 18.52 6.19 4.36 4.48 5.24 7.11 2.09 9.03 5.86 7.04 8.01 4.32 3.70 8.70 8.08 8.39 6.42 <151.43 1213.95 <77.30 <69.86 <26.31 <46.58 <26.80 <24.00 <38.74 <28.07 201.47 205.21 398.29 10 fim 212.91 124.80 273.02 394.64 118.09 787.41 104.76 114.87 124.80 175.47 91.24 90.41 27.81 25.13 53.98 58.10 40.95 68.58 23.13 87.94 67.33 34.37 64.30 74.51 54.98 34.37 83.99 c ft/(A),IRAS(Jy) <0.18 <0.11 <0.11 12 fim25pim60/im100 <0.12 0.34 0.22 0.41 0.09 0.32 0.31 0.58 0.31 0.14 0.68 0.09 0.19 0.15 0.25 0.31 0.15 0.46 0.30 0.37 0.57 0.83 0.15 0.68 1.81 0.36 0.30 0.27 0.31 1.41 1.1 0.74 0.63 0.99 0.46 2.24 11.2413.78 0.99 0.91 0.56 2.33 8.52 0.51 0.91 0.66 1.15 0.67 8.11 1.31 16.019.6 1.54 10.83 1.52 II. 0 0.76 I. 15 2.52 2.04 1.32 1.68 2.05 0.60 0.98 1.30 5.44 0.57 1.72 1.15 104.08 33.60 23.70 20.50 7.36 11.51 6.97 14.25 5.39 43.7 4.80 5.46 8.36 9.09 5.84 5.86 7.50 6.22 6.82 5.32 6.22 6.97 5.92 8.44 5.22 5.34 8.15 8.92 7.31 27.2 5.54 18.3 19.4 117.69 30.89 22.31 33.63 19.63 16.20 24.80 15.68 10.84 10.35 13.26 11.60 12.83 11.13 10.28 7.95 9.91 9.40 7.95 9.11 32.0 7.49 9.42 5.86 22.8 43.0 8.81 37.5 4.64 8.99 361 1988AJ 95. . 35 6C l a c /um fluxdensityfromthermalemissiongraduallyincreases Ä (1.3/1.6)indicatesdustabsorption, asseenmostclearlyin number maybemuchlarger.The largedispersioninÆ(3.7/ at Visbetween0and10,although forafewobjectsthis tions fromhotdustemissiontoanormalgalaxycomponent. relative tothecontributionat3.7¡umfromanormalgalaxy. Fig. 3(a).Formostofthegalaxies, theinferredopticaldepth dust appliedtoanormalgalaxy component.Therangein tios oftheLBGsaregenerally consistent withtheeffectsof to anormalgalaxy,andindicatethechangeinflux-den- Lines b,c,anddwillbetakenasrepresentativeofcontribu- sity ratiosofanormalgalaxyasthecontributionto3.7 appropriate fordustgrains(see,example,Draineand Lee 1984).Thelinesemanatefromthepointcorresponding law fromCohenetaL(1981); creasing theopticaldepth,usingnear-infraredreddening the flux-densityratiosofanormalgalaxybygraduallyin- 800 K(linec),and1000d),withÀ~emissivity, source (linea);thelineindicatesreddeningproducedon and 3(b)aretrajectoriesofthefollowingphysicalprocesses: the twoindividualcomponents.AlsoshowninFigs.3(a) will lieonastraightlineconnectingtheflux-densityratiosof 1.6) cannotbeduetoextinction (linea),butisconsistent investigated furtherinFig.3,whereÆ(1.3/1.6),R(2.2/ components AandBfromFig.2areindicatedinFigs.3(a) tent withcombinationsofnormalgalaxyemissionandemis- their near-infraredratios,manyoftheLBGsarealsoconsis- thus consistentwithacombinationofnormalgalaxyemis- ratios forcombinedcontributionsfromanytwocomponents common wavelengthforthedenominator,flux-density and 3(b).Sincetheratiosareplottedonalinearscale,with sion fromastarburstnucleus. sion plusdirectemissionfromanAGN.However,basedon 1.6) ,andR(10/3.7)areplottedagainstR(3.7/1.6).The 362 CARICOETAL.:IRASGALAXIES NGC 3690.Thisobjecthasadistortedmorphologywithnumberofknotlikestructures.Measurement(a)isthevisualpeak;measurements(b) IRAS 1017+08.Therearetwovisuallyobviousnuclei;measurement(a)istotheeastof(b). centered onthenorthwesternmostnucleus. IRAS 0857+39.Therearetwovisuallyobviousnuclei;measurements(a),(b),and(c)centeredbetweenthemeasurement(d)is and (d). MCG —03-12-002.Therearetwovisuallyobviousnuclei;thenucleusinmeasurements(a)and(bis20"northofc NGC 5256.Therearetwovisuallyobviousnuclei;measurement(a)isnorthof(b). NGC 4922.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is10"north,20"eastof(b). and (c)areeastnorthof(a),respectively. IRAS 0335+15.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is10"eastof(b). NGC 1143/4.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is40"west,20"northof(b). and (c)is5"eastof(b). MCG +024-24-025.Therearethreevisuallyobviousnuclei;thenucleusinmeasurement(a)isnorthernmostnucleus,(b)10"southof(a), the entireobject.Measurements(b)and(c)areofeasternmostposition,15"east(a)(d). of thesestructuresareseparatenuclei.Measurements(a)anddthevisualalso2.2yumpeak,lyinginnorthwesternmostposition labels theindividualmeasurements,andcanbeusedtoidentifythesemeasurementsinTablesIIIIV.Galaxiesmeasuredatmorethanone Someofthegalaxiesweremeasuredwithmorethanonebeamdiameter,andsomeatposition.Forsuchcases,ObservationCode NGC 7592.Therearetwovisuallyobviousnuclei;measurement(a)iseastof(b). IRAS 1713+53.Therearetwovisuallyobviousnuclei;measurement(a)isnortheastof(b). NGC 6090.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is10"northeastof(b); NGC 5257/8.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)isnorthwestof(b); UGC 8335.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is40"southeastof(b). UGC 2369.Therearetwovisuallyobviousnuclei;thenucleusinmeasurement(a)is20"northwestof(b). IC1623. Thisobjectcontainsanumberofvisibleknotlikestructures,althoughitwasnotpossibleatthetimeobservationstodeterminewhich Thesymbol

b c NAME OBS FLUX DENSITY RATIOS R¡¿ LOG[LIR/L@] CODEa R( 1.3/1.6) R(2.2/l .6) R(3.7/1.6) R(10/3.7) R(12/25) R(25/60) R(10Q/60) r- oo —' o d es i-HOooi-Jdd^dd^dd^dd^^^^r^esdi-Hdd^^i-ídr-; pa\t^ONqoNoe>r-H en es O 1 >— O oo enos —< mon i < W w es d 0\ ^ -h P^ ^ Od d r-i enTfr ' ^ o en D Ü u d es »n d eS r-l en —i A S z O ^ U o 5 ? ^ 00 oo ^ 0 ^ o en «nrn A oi i-i o z u es punoo en soi—i odd r- oo oes un es d o o u Ö d O £ S ; A z o u wn en d do oo nor- o onun d i-¡ 1-1 O00Os o S cd X5X) i—' r-'unrf o Provided bythe NASA Astrophysics Data System v Ü u en On v O D o u un d en r- ^noon p .-Hir¡ --i i-íes c 0T) oí NO ON oo mun d d i-i r- ^o'^i-ñ—¡^-¡oddi-í^d NOONOOeS—^OnOnOnOOOn enenooQenOeSOON^-QNen d r-~ r- es oo un esooen O i—

MCG-03-57-017 0.67 1.07 1.32 5.90 0.32 0.18 1.93 0.54 11.23 366 1988AJ 95. . 35 6C 367 CARICOETAL.:IRASGALAXIES © American Astronomical Society • Provided by the NASA Astrophysics Data System H % S' S w co W ° 8 PQ Q gJ ^ g ® Q îz; et; g § ai p ai 1 0 en d 2 »n tí- d r-3^ os en S O o O »-Hr-H S V î es ^r-4 CS 00rHTtso »-h «nminen Z O U $ s Tf Tt so r- en S en in R 8 2 O T-Hr-H q —io es en o q Z o U Os d ’-Hr-H os »no WH SDr-lr-iIT) d $ Z O Ü U »n noo »n enTt odd en Ttes en oo odd en o»-i Os Tt odd r- r- o q wn S f2 3 es o -Z ti¿ ^•1 * si ■< B > S •5 T3 1 ë 1 I Ü ex g O o bb 8 B 0 § § S 1 367 1988AJ 95. . 35 6C 12 12 ratios R(100/60),Ä(25/60and R(\2/25)areplottedver- shown inFig.4,wherelogarithms oftheIRASflux-density tent withdirectAGNemission,canbemodeledbyinvoking was seeninFig.2,theflux-densityratiosformanyof from hotdustintheenvironmentsofveryyoungstars.As frared propertiesthroughabsorption,aswellemission a substantialemissioncomponent fromdustat~500K. comparison toalloftheotherLBGs,andcertainlyinconsis- AGN. Suchanextreme3.7[imexcess,althoughuniquein ity of1.2X10L,hasbeenstudiedbySandersetal. acterized bylargequantitiesofdust,affectingthenear-in- Regions ofrecentorongoingstarformationwouldbechar- strain theintrinsicsourceofluminosityinLBGs. largei? (3.7/1.6)ratioof26.56.Thisgalaxy,withaluminos- 0857 +39,whichisclearlydistinct,duetoitsextremely be usedtonarrowdowntheluminosityrangewherein 368 CARICOETAL.:IRASGALAXIES transition toadominantactivenucleusoccurs. to hot-dustemission.Hence,thenear-infraredratioscannot frared flux-densityratiosthatcanbereadilymodeledasdue tified asprobablycontainingactivenuclei,havenear-in- with L>10,whichSandersetal.(1988)haveiden- ed bydustemission.ThisisseeninthefactthatLBGs would alsoexpectthenear-infraredemissiontobedominat- nucleus. However,foraheavilydust-enshroudedAGN,one LBGs areconsistentwithacontributionfromstarburst (1988), whoclaimthatitsprimarysourceofpowerisan 0 ir0 The luminositydependenceofthe far-infraredemissionis There isonegalaxyfromtheLBGsample,IRAS © American Astronomical Society • Provided by the NASA Astrophysics Data System son 1977). representative ratiosfornormalgalaxies(fromAaron- and 1000fim(seethetext).Thedashedlinesindicate squares). Lisanestimateoftheluminositybetween8 sample ofIRASgalaxiesstudiedbyCaricoetal.(1986; the infraredluminosity,forLBGs(circles)anda Fig. 1.Thenear-infraredflux-densityratios(a)i?(1.3/ 1.6) and(b)Æ(2.2/1.6),plottedlogarithmically,versus IR b) IRASData 1 n 1 1 12 9 R (25/60)withluminosityabove10L.Thislackofcor- butions between12and25/zm. luminosity (PaperI).Asimilareffecthasbeenfoundfor tive minimumintheradiationfieldwhichincreaseswith material, whichisindependentofluminosity,andaneffec- tive maximumintheradiationfieldheatingradiating with increasingluminosity,havebeenattributedtoaneffec- but requiresatleasttwocomponents. Thedatasuggesta to theflux-densityratiosforsteady-state emissionfromdust the LBGs,Fig.5(b)showslocusofpointscorresponding ber oftheLBGs,Ä(12/25)ratiosareconsiderably L>5xl0 havelog[R(12/25)]>-0.5.Thus, frared galaxiesdoes,infact,continuedowntoluminosities relation betweeni?(25/60)andinfraredluminosityforin- Soifer (1985). Seyfert galaxies;see,forexample,Miley,Neugebauer,and and anapparentmaximumR(100/60),whichdecreases mum R(100/60)ratio,whichisindependentofluminosity, cold-dust component,with characteristic temperatures the LBGscannotbemodeledwith asingledusttemperature, can bereadilyseenthatthefar-infrared emissioninmostof grains, withÀ~emissivity,at arangeoftemperatures.It or Seyfertgalaxiesindicatingunusuallysteepenergydistri- smaller thanthecharacteristicratiosfornormal,starburst, fert galaxies.OnestrikingfeatureofFig.5isthat,foranum- in thesensethatalthoughalmosthalfofgalaxies those giveninPaperI. data includedinthispaperdonotdiffersignificantlyfrom mentioned previously(Sec.Ill),the60and100/zmIRAS plotted againstLfortheentireBrightGalaxySample.As sus L.Figure4(a)isessentiallythehigh-luminosityendof not havefar-infraredemissionconsistentwithtypicalSey- luminosity range1-5XlOLhavelog[i?(12/ another flux-limitedsampleofIRASgalaxies. Fig. 6(a)inPaperI,whichshowsf(60(100//m) pear tobepoweredbyactivenuclei(Sanderseiö/.1988),do luminosities andhighR(12/25)ratios. there appearstobeanabsenceofgalaxieswithveryhigh emphasizing thattheLBGswithL>10,whichap- relatively flatenergydistributions.Inparticular,itisworth IRAS measurementsisthustakenintoaccountinthecom- where characteristicflux-densityratiosfornormal(N), compared tothoseofotherextragalacticobjectsinFig.5, 25)] >—0.5[J?(12/25)>0.3],noneofthegalaxieswith which istypicallylargerinSeyfertgalaxies,reflectingtheir with datafromotherauthors(see,forexample,Sekiguchi Rowan-Robinson andCrawford(1986),areconsistent points N,B,andSweredeterminedbasedonthedatafrom starburst (B),andSeyfert(S)galaxiesareincluded.The are distinctfromSeyfertgalaxiesinthei?(25/60)ratio, are similartothoseofnormalandstarburstgalaxies.They parison. galaxies werechosentorepresentthefar-infraredflux-den- Since alloftheLBGsarevisuallyextendedsources,Seyfert any far-infrareddiskemissiondetectedbythelarge-beam sity ratiosofactivegalaxies,ratherthanthequasar3C273; 0 IR0 ~10L, asdemonstratedbySmithetal.(1987)using 1987; Helou1986;Miley,Neugebauer,andSoifer1985). fir ir 0 v IR0 o The effectsseeninFig.4(a),namelyanapparentmini- To investigatethesourceoffar-infraredemissionin In Fig.4(b),theredoesnotappeartobeanychangein In Fig.4(c),theR(12/25)ratiochangeswithluminosity The far-infraredflux-densityratiosfortheLBGscanbe The far-infraredflux-densityratiosformostoftheLBGs 368 1988AJ 95. . 35 6C 7-5 luminosity seeninFig.4(b)suggests thatthecharacteristic viously. Thelackofanycorrelation betweenR(25/60)and tially equivalenttotheresultfrom PaperImentionedpre- dust contributingtotheirinfrared luminosity.Thisisessen- er galaxiesarefoundthathave significant quantitiesofcold the entireluminosityrange,asL increases,fewerandfew- with littleornocontributionfrom colddustarefoundover pendence seeninFig.4(a)indicatesthat,althoughgalaxies IRAS galaxies(see,forexample,PaperI;DeJongetal. reflected intheR(100/60)ratio.Thus,luminosityde- infrared emissionfromcold(T—30-50K)dustisprimarily bution fromanadditionalwarmercomponent,attempera- nosity scalesroughlywithtemperatureasT. nent, sincethemassofdustrequiredtoproduceagivenlumi- the dataisprobablyappropriateforcold-dustcompo- ty seeninPaperI.Thehighesttemperatureconsistentwith ies, butarehigherthanthoseexpectedforlower-luminosity tures r>70K.Suchtemperaturesareinagreementwiththe results ofSekiguchi(1987)forhissamplestarburstgalax- T —30-50K,formostofthegalaxies,coupledwithacontri- IR 1984) andreflectthedecreaseinR(100/60)withluminosi- 369 As Fig.5(b)shows,therelativecontributiontofar- © American Astronomical Society • Provided by the NASA Astrophysics Data System CARICO ETAL.:IRASGALAXIES from Neugebauera/.(1987).ForpointB,R1.3/1.6)and2.2/1.6areScovilleetal.(1985),andR(3.7/1.6)is from Becklin,Fomalont,andNeugebauer(1973). flux-density ratiosrepresentativeofnormalgalaxies(N),activegalacticnuclei(A),andstarburst(B).Forpoint N, i?(1.3/1.6)and^(2.2/1.6)arefromAaronson(1977),Æ(3.7/1.6)isLawrenceetal.(1985).PointA that, duetothedifferentdispersionsinratios,scaleshavebeenusedforaxes.Alsoshownare coordinate system.Thesmallercirclesandasterisksindicatetheprojectionsofdataontoeachaxisplanes.Note Sanders etal(1988)areplottedwithanasterisk.Thedataonthejc,y,andzaxesofastandardright-handed Fig. 2.Near-infraredflux-densityratiosÆ(1.3/1.6),R(2.2/1.6),andÆ(3.7/1.6).TheLBGspreviouslystudiedby 7 resulting inlargeR(12/25)ratios. Astheintensityof affected bytheemissionfrom PAHs inthe12¡imband, state. Forrelativelyquiescent,inactive galaxies,R(12/25)is the R(12/25)ratioreflects relativecontributionsfrom known asPAHs(LegerandPuget 1984).InHelou’smodel, PAHs andfromlarger,hot-dust grainsradiatinginasteady these smallgrainsarepolycyclic aromatichydrocarbons, wavelengths between1and20fim.Evidencesuggeststhat roughly 1000K,canbeanimportantsourceofemissionat grains (~afewAngstromsinsize),transientlyheatedto gren 1984)havediscussedthepossibilitythatverysmall ple, Desert1986;Puget,Leger,andBoulanger1985;Sell- proposed byHelou(1986).Variousauthors(see,forexam- R (100/60)arecorrelated.Thus,as12/25)increases,in- cates acoldertemperatureforthedustemittingat60and emitting at12and25¡im,theincreaseinÄ(100/60)indi- dicating ahighercharacteristictemperatureforthedust tematically withluminosity. temperature ofthedustwithT^:70Kdoesnotchangesys- 60)], presentstheinterestingresultthatR(12/25)and 100//m. Aplausibleexplanationforthiscorrelationhasbeen @ Figure 6,whichshowslog[R(12/25)]vs[R(100/ 369 1988AJ 95. . 35 6C fact thattheLBGsaresystematically moreluminousthan formation activityintheLBGs. Thisisconsistentwiththe which, usingHelou’smodel,implies ahigherlevelofstar- smaller R(12/25)ratiosthan donormalIRASgalaxies, nificantly affecttheobservedrange inR(12/25)orÆ100/ though thisdistinctioninÄ(25/60) doesnotappeartosig- by thedashedenvelopeinFig.6.Forcomparison,LBGs 60) fortheLBGs.Itisseenthat, onaverage,theLBGshave with /£(25/60)>0.18havebeenidentifiedinFig.6,al- galaxies withÄ(25/60)>0.18;Helou’sdataareindicated likely Seyfertcandidatesbyremovingfromthesampleall from asampleofnormalIRASgalaxieschosentoexclude and determiningtheIRAScolors. dust grainsincreases,dominatingthefar-infraredemission heating radiationinthegalaxyincreases,aswithincreased star formation,theequilibriumtemperatureoflarger 370 CARICOETAL.:IRASGALAXIES The datausedbyHelou(1986)inhisanalysisweretaken © American Astronomical Society • Provided by the NASA Astrophysics Data System 1ru hot-dust emission(nocontributionfromanormalgal- The arrowspointtowardtheflux-densityratiosofpure tio forthisgalaxy. tion ofeacharrowgivestheappropriateflux-densityra- extending fromanapparentdatapoint;theverticalposi- ratios forthegalaxyIRAS0857+39,whichi?(3.7/ and astarburstnucleus(B),asinFig.2.Theflux-density densities representativeofanactivegalacticnucleus(A) sentative ofnormalgalaxies(fromAaronson(1977)and axy). Thelinesathroughdextendfromthepointrepre- mal-galaxy emission,andaredrawnatintervalsof10%. total 3.7(imemissionfromdustemission,relativetonor- Lawrence (1985);seethetext).Alsoshownareflux tions fromhot-dustemissionatT=600,800,and1000 the source,labeledasafunctionofopticaldepthatV, been excluded.Thelinesathroughdrepresentthefol- jR( 10/3.7),plottedagainstÄ(3.7/1.6).TheLBGspre- K, respectively;thetickmarksindicatefractionof T where/„ocr“(1—e“);b,c,andd=contribu- lowing: a=absorptionfromdustuniformlymixedwith an asterisk.Galaxieswithonlylimitsat3.7orlO/xmhave viously studiedbySandersetal.(1988)areplottedwith Fig. 3.Flux-densityratios7?(1.3/1.6),2.2/1.6),and 1.6) =26.56,areindicatedineachplotbyashortarrow vi 0 123 [H -L](mag) and Ä(12/25)versustheinfraredluminosityfor LBGs. TheLBGspreviouslystudiedbySandersetal. Fig. 4.IRASflux-densityratios/?(100/60),Æ(25/60), ( 1988)areplottedwithanasterisk. burst galaxies(B),determinedusingthe dataofRowan- vity proportionalto A locus offlux-densityratiosfordustemission withemissi- of normalgalaxies(N),Seyfert (S),andstar- studied bySandersetal.(1988)areplotted withanaster- Robinson andCrawford(1986).Thecurve in(b)isthe isk. Alsoshownaretheflux-densityratios representative and i?(100/60),fortheLBGs.The LBGs previously Fig. 5.IRASflux-densityratios,Ä(12/25),^(25/60), 0 0.20.4 R(25/60) Lir/Lq 370 UDu 00LO 371 CARICO ETAL. ; IRAS GALAXIES 371 COLO some of these galaxies. In particular, for Arp 220 the visual extinction corresponding to the depth of the silicate feature observed has been estimated by Becklin and Wynn-Williams 00 ( 1987) to be ~50 mag. In a more detailed analysis than is CO given here, these authors find that more than 90% of the 12 pm emission from Arp 220 is contained within a 3" diameter about the nucleus, whereas the value of R10 presented in this paper for this galaxy is only 0.63. Arp 220 is most likely a very extreme case, but nevertheless, more accurate values for R10 would be somewhat higher than those presented here. The extent of the \0pm emission is potentially an effective diagnostic of the relative AGN contribution in a galaxy, since dust sufficiently hot to radiate in a steady state at 10 pm must be at a temperature of several hundred degrees, and hence must be comparatively close to the luminosity source. For dust at 300 K (which corresponds to a peak in the ther- mal energy distribution at 10 pm, if the dust emissivity is proportional to frequency), illuminated by a source of lumi- 11 Fig. 6. IRAS flux-density ratio R ( 12/25 ) versus R ( 100/ nosity ~ 5 X 10 L0, characteristic distances are on the or- 60), plotted logarithmically. The LBGs previously stud- der of one hundred to a few hundred parsecs. Thus, substan- ied by Sanders et al. ( 1988) are plotted with an asterisk. tial 10 pm emission beyond this distance from the nucleus The dashed envelope is from a sample of normal IRAS cannot be due to dust directly heated by an AGN, and galaxies, chosen to exclude likely Seyfert candidates, should generally be attributed to a distributed luminosity studied by Helou (1986). Squares indicate LBGs with source, such as star formation. Æ(25/60) >0.18 (see the text). In Fig. 7, the fraction of the total 10 pm emission within the ground-based 10 pm beam is shown for the LBGs, by plotting i?10 versus the \0pm beam diameter, in kiloparsecs the galaxies in Helen’s sample. Furthermore, the luminosity at the source. Most of the galaxies have significant 10 pm dependence seen in Fig. 4(c) implies that all galaxies with emission beyond 1 kpc in diameter, providing evidence that Ljr ^5XlOn Z,0 have sufficient quantities of large dust enhanced star formation contributes substantially to the in- grains radiating at high temperatures to dominate the 12 and trinsic luminosity in most of the LBGs. The possible excep- 25 //m emission. This agrees with the earlier result (Sec. tions to this are those galaxies with R 10~ 1, for which the 10 I Va) that the infrared luminosity is correlated with hot-dust pm diameter is an upper limit on the spatial extent of the 10 emission at near-infrared wavelengths. pm emission.

c) 10 iim Measurements: The Spatial Distribution of the Infrared Emission The diameter of the lOyum measuring beam corresponds to a 3 kpc median diameter at the source and a median dl0/ D0 of 0.1, where d10 is the 10/¿m beam diameter and D0 is the visual major-axis diameter measured from the Palomar Ob- servatory Sky Survey prints. Since the IRAS detectors typi- cally subtended I!5x4!75, whereas the visual diameter DQ for the LBGs is typically 0Í2 to 1!4, the IRAS data represent the total emission from each source, independent of D0. Hence, a comparison of the ground-based 10 ¡am data,/v ( 10 //m, small beam), with the IRAS 12 ¡um data,/v( 12 ¡um, IRAS), gives an estimate of the spatial extent of the 10 pm emission in these galaxies. To adjust for the 10-12/2m color, a power law extrapolation through 25 and 12pm was used to estimate the total 10pm flux density,/v ( 10pm, total), for each galaxy, and a second power law extrapolation through 3.7 and 10 pm was used to estimate the 12 pm flux density which would have been measured in a ground-based beam of the same diameter as the 10 pm beam, /v(12 pm, small Fig. 7. Fraction of the total 10 pm emission measured in a beam). The ratio Ä10 of the \0 pm flux density measured in 5" beam plotted as a function of the 10//m beam diameter, the ground-based beam to the total \0 pm flux density was in kiloparsecs source. Galaxies with only limits at 10/im or then taken as the average offv (\0pm)/fv ( \0pm, total) and 12 pm (see Table II) have not been included. The LBGs / ( 12 pm, small beam)// ( 12 pm, IRAS). Hereafter, R previously studied by Sanders etal. ( 1988 ) are plotted with v v l0 an asterisk. The curves indicate exponential brightness dis- will be used to characterize the degree of concentration of tributions where the surface brightness falls to 1% of its the 10 pm emission about the nucleus of each galaxy. Rl0 is peak brightness at a radius D /2 ( see the text ) ; curves have tabulated in Table IV. been drawn for r0 = 0.5, 1.0, and 2.0. The 10pm emission No attempt has been made to correct the values of R10 for within a 9.4 kpc diameter about the nucleus of M101 is silicate absorption, which is known to be strong for at least shown for comparison (Rice 1987).

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1988AJ 95. . 35 6C 10 fim emissionwithina9.4kpcdiameteraboutitsnucleus L ),andislargeenoughforinformationonthespatialdis- 372 CARICOETAL.:IRASGALAXIES results verysimilartothatofM101(Rice). erate-luminosity gas-richspirals,M51andNGC891,yield tive ofgas-richspiralgalaxiesmoderateluminositydetect- more extendedthanthatinmostoftheLBGs.M101was have irregularmorphologies,inmanycasesapparentlydue for example,MihalasandBinney1968).MostoftheLBGs responds tothediskemissioninnormalspiralgalaxies(see, distribution proportionaltoexp(—r/r),withr=0.5, tribution tobeobtained.TheIRASdatafortwoothermod- ed byIRAS(fromPaperI,theluminosityofM101is2X10 chosen forcomparisontotheLBGsbecauseitisrepresenta- galaxy M101hasbeenindicatedinFig.7byplottingthe12 profiles wouldbewellrepresentedbyanexponentiallaw. to galaxycollisions,soitisunlikelythattheirbrightness number forcharacterizingthebreadthoflightdistribu- teristic ofacompactnuclearinfraredsource. sizes r<0.5kpc,asizeHill(1987)hasshowntobecharac- tion. Itisseenthatroughlyone-thirdoftheLBGshavescale Nevertheless, theexponentialscalesizercanbeauseful outside oftheground-basedbeamhasabrightnessprofile does notprecludethepossibilityofanadditional,substantial galaxy mustbeduetoadistributedsource,suchemission originates, onecanestimatethemaximumpossiblecontribu- appropriate fornormal-galaxydiskemission,andbysetting source. Byassumingthatthe10//memissioncomingfrom contribution tothetotalluminosityfromacentralpoint is consistentwiththeobservedvalueforR.Sincenogalax- tion tothe10//memissionfromacentralpointsourcewhich a limittothediameteroutwhichthis10^mdiskemission 0 ed beyondtheopticaldisk(Riceetal.1987)Dcanbetaken ies areyetknownwheresignificant12//memissionisdetect- 1.0, and2.0kpc.Anexponentialbrightnessdistributioncor- (Rice 1987).Itisclearthatthe10¡imemissioninM101 as alimittotheextentof10/¿mdiskemission.Anesti- 0 o 0 10 0 Also showninFig.7arefluxintegralsforabrightness An estimateoftheextent10fimemissionin Although 10¡imemissionbeyond1kpcofthecentera © American Astronomical Society • Provided by the NASA Astrophysics Data System 12 ¿ir >10Lq.Galaxieswithonlylimits at10or12fim(see Table II)havenotbeen includedineitherhistogram. text). Solidline:theLEGsample;dotted line:theLBGswith the 10/zmemissionfromacentralpoint source,R(seethe Fig. 8.Histogramsofthemaximumpossible contributionto PS Rps n 1 1 1 12 12 Lir ~10Liscorrelatedwithincreasedemissionfrom R (3.7/1.6)and2.2/1.6forsuchgalaxiesrelativetolow- Lir >7X10L),thereisnocorrelationbetweenRand mate, Rofthemaximumpossiblepoint-sourcecontribu- dust contributesasubstantialfractionofthe2.2and3.7/im was thusobtainedbymodelingthespatialdistributionof tion totheobserved10fimfluxdensityforeachofLBGs er-luminosity galaxies.Thisexcesshot-dustemissionap- emission, resultinginagreatlyincreaseddispersion hot dustwithcharacteristictemperatures~800K.This results: greater thanorequalto10Lhasyieldedthefollowing optical diameter. less than50"(asizethatincludes12ofthe14LBGswith a selectioneffectsince,forgalaxieswithangulardiameter sion doesdecreaseabruptlyabovethisluminosity.Thisisnot population ofgalaxieswithbroadlyextended10fimemis- nosities belowapproximately7X10L.However,the not appeartobeanyluminositydependenceinR,forlumi- ted againsttheinfraredluminosityforLBGs.Theredoes has beeninvestigatedfurtherinFig.9,whichshowsRplot- gram haveR>0.4.Thispossibleluminositydependence of thesevengalaxieswithL>10plottedinhisto- the degreeofconcentration10/¿memission,sincesix ¿ir >10L.Thedataforroughlytwo-thirdsoftheLBGs more fromapointsource. the galaxiesareconsistentwithacontributionof50%or total 10¡imemissionfromacentralpointsource,andhalfof are consistentwithacontributionof20%ormoretothe Fig. 8,fortheentireLBGsampleandalsoLBGswith 0 peak brightnessataradiusD/2.Theresultsareshownin exponential diskwhosesurfacebrightnessdropsto1%ofits 01 PS 0 0 10 10 PS IR0 0 10 /¿memissionasacentralpointsourcecoupledwithan 0 An analysisof61IRASgalaxieswithinfraredluminosities Figure 8alsoshowsapossibleluminositydependencefor ( 1)Anincreaseinthetotalinfraredluminosityabove based beamtothetotal10fimemission, versusthein- plotted withanasterisk. at 10or12//m(seeTableII)havenotbeen included.The frared luminosityfortheLBGs.Galaxies withonlylimits Fig. 9.TheratioÄofthe10//memission intheground- LBGs previouslystudiedbySanders et al.(1988)are 10 V. CONCLUSIONS LirAo 372 1988AJ 95. . 35 6C 1 1 plained asanincreaseinsilicateabsorptionduetoin- hotter temperaturesinthesegalaxies,butcanalsobeex- which mayrepresentashiftinthetemperatureofdustto hot dusthavesystematicallysmalleri?(10/3.7)ratios, crease inthemassofdustthesegalaxies. the largestcontributiontonear-infraredemissionfrom pears to“turnon”atluminosities—10Lq.Galaxieswith infrared galaxiesgenerallyspantherangefromnormalto have steeperenergydistributionsbetween12and25¡imthan IRAS PointSourceCatalog(1985).(U.S.GPO,Washington,DC). de Jong,T.,Clegg,P.E.,Soifer,B.Rowan-Robinson,M.,Habing,H.J., but requiresacontributionfromcolddust(T~30-50K) propriate fortypicalSeyfertgalaxies. galaxies presentedinthispaperhaveflux-densityratiosap- are expectedfromnormalorstarburstgalaxies.Noneofthe Désert, F.X.(1986).InLightOnDarkMatter,editedbyP.Israel Cohen, J.G.,Frogel,A.,Persson,S.E.,andElias,H.(1981).As- Carico, D.P.,Soifer,B.T.,Beichman,C,.Elias,J.H.,Matthews,K.,and Draine, B.T.,andLee,H.M.(1984).Astrophys.J.285,89. 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