1987ApJ. . .318. .595C examined theopticaltofar-infraredenergydistributionsof National OpticalAstronomyObservatories, operatedbytheAssociationof lished: dustnearthenucleusmayabsorbopticalandultravio- was well-establishedandisnosurprise:starscooldustin could beprimarilytheresultoftwosimpleeffects.Oneeffect have aconfusingvarietyofforms,PaperIsuggestedthatthese emission fromdust.MacAlpine(1985)hasmadeastrong case varied muchlessintheinfraredthanopticaland con- hereafter EM)gofurther,attributingthebulkofemission nonthermal componentat3.5/mi.EdelsonandMalkan(1986, red continuaofSeyfert1galaxiesarethermalornonthermal. let lightandreemititthermallyintheinfrared. nuclei. Theothereffectwassuggestedbutnotfirmlyestab- This contaminationisespeciallyimportantforlow-luminosity the hostgalaxycontaminateemissionfromnucleus. Science Foundation. Universities forResearchinAstronomy, Inc.,undercontractwiththeNational tended thatthebulkofemissionbeyond1/miisthermal other hand,RiekeandLebofsky(1981)foundthatNGC4151 at allinfraredwavelengthstononthermalemission.On the by theUniversityofHawaiiundercontract withtheNationalAeronauticsand Stein andWeedman(1976)foundevidenceofasubstantial Seyfert 1galaxies.Althoughtheobservedenergydistributions Space Administration,andtheCerro TololoInter-AmericanObservatory, The AstrophysicalJournal,318:595-611,1987July15 © 1987.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. 1 A precedingpaper(Wardetal1987,hereafterPaperI) There hasbeenacontinuingdebateaboutwhethertheinfra- BasedondatatakenattheInfrared TelescopeFacility,whichisoperated energy distributionsaremainlynonthermalbutmayhavethermalcontributionsatwavelengthsthatdifferin photons; dereddeningwouldremovethisdeficiency.Weconcludethat,ingeneral,theobjectswithflattest individual wavelength.Moreover,extrapolationoftheobservedsteepspectrasuggestsadeficiencyionizing component intheinfraredisbettercorrelatedwithhardX-rayluminositythanfluxdensityatany Subject headings:galaxies:Seyfert—infrared:spectraspectrophotometry range ofdistancesfromthenucleiasemission-lineregions. different objects,whiletheobjectswithsteepspectraaremainlythermalexceptatwavelengthsshorterthan give considerableevidenceforthishypothesis;example,asimplydefinedupperlimitthenonthermal ent “steepspectrum”objectsshowingacombinationofreddeningatshorterwavelengthsandthermalemis- galaxies. Wepostulatethatthenonthermalcontinuaofallobjectsareintrinsicallysimilar,withappar- sion bydustatlongerwavelengths.Correlationsbetweeninfrared,hardX-ray,andemission-lineluminosities sample; allgalaxiesinthesamplehavebeenmeasuredhardX-rays,andmostturnouttobeSeyfert1 a sampleofactivegalacticnuclei.TheisdominatedbythemembershardX-rayselectedcomplete ~2 /un.Theinferreddustdistributionscanhavesubstantialcoveringfactorsandextendovermuchthesame © American Astronomical Society • Provided by the NASA Astrophysics Data System We attempttodistinguishbetweenthermalandnonthermalcontributionsthe1100¡xm.continuumin THE CONTINUUMOFTYPE1SEYFERTGALAXIES.II.SEPARATINGTHERMALAND I. INTRODUCTION Institute ofAstronomy,Cambridge,England;andAstronomyDepartment,UniversityWashington N. P.Carleton,MartinElvis,G.Fabriano,andS.Willner Received 1986OctoberS;acceptedDecember24 1 NONTHERMAL COMPONENTS Harvard-Smithsonian CenterforAstrophysics Queen MaryCollege,London Martin Ward A. Lawrence ABSTRACT AND 595 either ofthesewouldsuggest thatitcomesfromthesame is muchmoreextended(WilsonandHeckman1985).Evidence tant foratleastsomeobjects. dust mustbepresent.Rieke(1985)hasreviewedmuchaddi- and continuumemissionatvarious wavelengths.Theresultis search forthestrongestcorrelations betweenthesequantities region. Wehavethereforecollected emission-linedataforthe that thestrengthofinfrared emissioniscloselyrelatedto comes fromaverycompactregion(see,e.g.,Rees,Begelman, infrared emissiontothatatotherwavelengths.Forexample, tional evidenceandconcludesthatthermalemissionisimpor- that reddeningaffectsthevisibleandultravioletlines,thus and Blandford1981),whiletheopticalforbidden-lineemission there arestrongreasonsforbelievingthattheX-rayemission ponents (§II)isbasedonindirectcluesfromcomparisonof the ponent inthenucleusanditsrelationtocentralsourcelumin- find thatthisinterpretationoftheinfraredcontinuumis sup- energy distribution,whichismodifiedbydustabsorptionand Seyfert 1nucleicouldhavethesameunderlyingcontinuum Seyfert nuclei,togetherwith hard X-rayluminosities,andwe osity. temperature distributionoftheinfrared-emittingdustcom- ported byavarietyofdata.Finally,weaddressthespatial and thermal reemission.Wethenexamineadditionalevidence and thermal components.Basedontheresults,wepostulatethatall the infrared(1-100/mi)continuumintothermalandnon- approach. Weintroduceanempiricalmethodfordecomposing The decompositionintothermalandnonthermalcom- This papertakesarelativelysimplebutsomewhatnovel 1987ApJ. . .318. .595C a a physicallymeaningfulcomponent. under theinfraredregionwith anindexaä—1mayindeedbe indices arelistedindividually in Table1.Theaverageindexfor infrared powerlawshouldbemosteasilydistinguished for among power-lawslopessuggests thatapower-lawbaseline the classAobjectsisa=—1.02 +0.10.Thesmalldispersion class Aobjects.Figure2ashowsthedistributionofpower-law in aplotoflogv/(v)versusv,asindicatedFigure1. An slopes [for/(v)ocv]forthe 12objectsinclassA,andthe this componentisastraightlinethroughthelowesttwopoints law underliesthewhole1-100pmregion.Anupperlimit on continuum, thecurvatureisslightininfrared(Landauet al for objectsinwhichahigherdegreepolynomial(e.g., a parabola) givesabetterfittotheradiothroughultraviolet as theinfrared,coveringoneortwodecadesinfrequency.Even good approximationatleastinsectionsofthecontinuum,such in theinfrared.Nonthermalprocessesareusuallyconsidered in terms ofpower-lawspectra.Empiricallythisseemstobe a reddened AGNs. (class B)thatweconsiderascandidatesforsubstantially these 12objectsweredesignatedclassA.Thisleftnine fore havetheleastpotentialforthermalinfraredemission; 1986). Wethereforemaketheassumptionthatasinglepower tive ultravioletfluxdensitiesaretheleastreddenedandthere- densities. Weassumedthatthoseobjectswiththegreatestrela- were separatedbasedontheratioof0.36/mito1.2¡nmflux had insufficientdatatobeclassified.Theremaining21galaxies IR and theseobjectsweredesignatedclassC.Fourmoregalaxies both fromcooldustemissionat60-100/¿mandstarlight, appeared tohavestrongcontaminationfromthehostgalaxy, energy distributions.Typicaldistributionsareshownin Figure 1ofPaperI.Oftheoriginalsample34galaxies,nine Figure 1,andthedataforentiresamplewereshownin tion ofthedustandfindittobeplausible. lates withreddeningmeasures,aswouldbeexpectedfor thermal reemission.Finally,weexaminetheimplieddistribu- shows thatinfraredemissionatavarietyofwavelengthscorre- tinua, aswelltheemissionlines(MacAlpine1985).Itthen that reddeningisimportantforthevisibleandultravioletcon- dust inactivegalacticnuclei(AGNs).SectionIIIfirstshows makes itsingularlyvaluableforastudyoftheimportance neither towardnorawayfromobjectscontainingdust.This X-ray selectedsampleofPiccinottietal(1982),itisbiased our sampleisdominatedbythemembersofcompletehard sary tolookatthepropertiesofalargesampleobjects.As example, byLawrenceandElvis(1982).Itisthereforeneces- existence ofsomestructurelikeatoroidorthickdiskwhose orientation variesfromobjecttoobject,assuggested,for whole, owingeithertorandompatchinessofthedust,or attenuation inourlineofsightmaynotberepresentativethe would bestraightforward.Inreality,wemustexpectthat distributed aboutthesource,thentestingofhypothesis ponents isnoteasy.Ifthedustwereuniformlyandspherically really differentiatesbetweenthermalandnonthermalcom- correlated withthehardX-rays. that wecandefineaninfraredcontinuumlevelishighly 596 Our firsttaskistodefineaplausiblenonthermalcomponent Paper Idividedoursampleintothreegroupsbasedonthe Testing thehypothesisthatempiricaldecomposition © American Astronomical Society • Provided by the NASA Astrophysics Data System a) UnderlyingNonthermalComponent II. AUNIVERSALCONTINUUM CARLETON ETAL. infrared baselinemayinclude componentsofstarlightand actual datapointsispotentially thermal.(Thepowerabovethe power representedbythearea abovethelineandbelow under theinfraredbaselineis potentially nonthermal,whilethe “infrared baseline,”IR.The powerrepresentedbythearea line throughit.Wereferto this lowestvalueofv/(v)asthe in aplotofv/(v)therange1-100pmanddrawhorizontal mic bandwidth—ahorizontallineonourplotsofvf(v)versus v. IR usedinthecorrelationanalysis. comprise thedatashowninFig.2a.Thesolidlinesdenote“infrared of thermalandnonthermalcomponents:findthelowestpoint spectra, thenwehaveawayofmakingprovisionalseparation If weassumethatsuchapowerlawmaybepresentinall our baselines” drawnthroughthesinglelowestpoint;theserepresentvalues of law fitthroughthetwolowestpointsininfrared;slopesofthese lines data; seePaperIfordetailsandreferences.Thedashedlinesdenotethepower- represents thesimplecaseofconstantpowerperunitlogarith- approximation toanunderlyingnonthermalspectrum,as it the 6keVfluxdensities.StarlighthasbeensubtractedonlyfromNGC931 are UBVRphotometry.Thearrowsontherightmarginindicatelevelof points, squaresareground-basedJHKLMNQinfrareddataandcircles of atypicalobjectineachclassdefinedPaperI.TrianglesareIRASdata & b A powerlawwitha=1.0isveryattractiveasgeneral Fig. 1.—Theinfraredtoultravioletenergydistribution[logv/(v)vs.logv] IOO¿¿m 30/¿mIO/¿m3/í.m\fim0.3/¿.m log v(Hz) 1987ApJ. . .318. .595C infrared, andtherightside(b)showsindicesa_derivedbyconnecting1.25¡amfluxdensityofinfraredbaselinewithhardX-rays. IRx Fig. 2.—(a-b)Thedistributionofpower-lawindicesforclassAandBobjects.leftside{a)showstheaderivedfromlowesttwopointsin IR © American Astronomical Society • Provided by the NASA Astrophysics Data System f f f NGC5548 NGC4151 NGC3783 Akn120 III Zw2 NGC 5506 NGC931 NGC 526a ESO 141-G55 F9 NGC 2992 IC 4329A Mkn 509 Mkn 841 Mkn 1383 3C 273 Mkn 79 NGC 7469 NGC 7314 NGC 7213 NGC 7172 NGC 4593 NGC 4051 NGC 3227 ESO103-G35 . MCG -6-30-15 3A0557-385 ... MCG 8-11-11... 3C 120 NGC 7582 f a d c h IRASdatamissingfortheseobjects ;parametersdefinedonavailabledata. SeeTable2forreferences. er —f_T i-be,ow=[«JxI"(100/1.2). 2=secondpointusedwithXtodefine a. À=wavelengthofminimumvalue ofv/(v),between1and100/¿m. SB 1R B -‘-'above -‘-'observed^below Object n 0.8 1.0 0.0033 0.0091 0.0222 0.0325 0.0461 0.0898 0.0330 0.0163 0.0189 0.0352 0.0368 0.0366 0.086 0.0166 0.158 0.013 0.0061 0.0138 0.0078 0.0344 0.0205 0.009 0.0085 0.0023 0.0033 0.0073 0.0053 0.0167 0.0056 0.0058 Observed BalmerDecrementsandPower-LawParameters a IR >18 Ha/H/P 12.6 13.2 18 11.5(N) 19.2(N) 4.8 4.2 4.9 2.8 2.9 4.3 6.5 6.3 3.7 5.3 3.1 3.6 5.9 3.6 6.7(N) 6.2 5.1 5.1 3.3 5.6 -0.95 -0.96 -1.12 -1.09 -0.99 -1.03 -1.04 -0.95 -1.21 -0.85 -0.93 -1.08 -1.16 -1.21 -0.75 -0.87 -0.90 -1.40 -0.94 -1.39 -0.93 TABLE 1 Class A Class A Class C Class B Class B 100 100 100 100 100 60 20 10.2 10.2 10.2 2.2 2.2 4.8 4.8 4.8 3.5 1.2 1.2 1.2 1.6 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.6 1.2 1.2 100 100 100 100 100 100 100 100 0.8 1.01.21.4 20 60 60 60 10.2 1.2 1.2 1.6 1.2 1.2 1.2 1.2 1.2 L r 'above/^"'below a |R-X 0.69 0.48 0.14 0.22 0.41 0.48 0.34 0.18 4.06 0.86 0.61 0.77 2.91 2.71 2.18 2.92 2.33 3.51 3.40 3.65 1.57 1.19 5.41 1.04 1.08 1.43 1.36 1.63 1.17 log L h( 46.61 43.53 43.84 44.39 44.82 45.49 45.47 44.24 44.99 44.91 44.62 45.42 44.42 43.91 43.87 44.23 43.54 44.82 44.27 44.76 44.14 43.61 44.72 43.75 43.80 43.87 42.65 42.97 43.68 43.00 1.4 L log al 44.83 44.59 44.64 44.57 43.76 46.22 43.56 44.04 44.47 44.50 45.02 44.73 43.67 45.03 44.88 44.83 44.57 44.17 44.03 44.69 44.14 43.66 42.54 43.44 43.98 44.46 44.41 45.25 43.56 1987ApJ. . .318. .595C a 2 23- with theX-rayregion. ponent withastrong,nonluminosity-dependentcorrelation cussion intheAppendix).Itthusappearsthatinfrared baseline indeeddefinesavaluefornonthermalinfraredcom- IR with[6keV]isthemorefundamentalcorrelation(see dis- indeed significantlybettercorrelatedwith[6keV]than is for thenineclassBobjectsis a_ =—1.03±0.04.First,itis shows thatforthecompletesampleofAandBobjects,IR is result ofthepartialSpearmanranktest,listedinTable4, luminosity. Thiscorrelationisthebestofall.Thequantitative value forthe12classAobjects isa_=—1.05±0.05and infrared baselinetothe6keVpoint.Theresultsofthisexercise (Malkan 1984)andtheleastdependenceonluminosityof are listedinTable1anddisplayed inFigure2.Theaverage flux density.Wemakethecomparisonbydefininganindex [3.5 /¿m]with[6keV].Thissuggeststhatthecorrelation of tion betweentheinfraredbaselineIRandhardX-ray directly observedquantities.Figure3alsoshowsthecorrela- iR-x f°rthepowerlawthatconnects1/miendof the osity correspondingtov/(v),wherev is thefrequencycorrespondingto20/an. obtained bycomparingitsactualfluxdensitytothehardX-ray [6 keV]standsoutastherelationwithleastscatter luminosity. menon simplyscaleswithluminosity.Véron-Cetty,Véron,and scaling holdsoveravarietyoftypesAGNincludingSeyfert the ultravioletspectraofAGNs.Shuder(1981)foundthat Tarenghi (1983)reachedasimilarconclusionthroughstudying with highsignificance(Table3)butvaryingdegreesof b scatter. ThisimpliesthattofirstordertheentireAGNpheno- IRx b resenting 3C273,themostluminousandUV-rich plot showsalineofunitslopepassingthroughthepointrep- IRx object inthesample. nation fromstarlightcouldbethegreatest.Forreference,each & several lowerfrequencies,omittingthoseatwhichcontami- shows thecorrelationsbetweenluminositiesinX-raysand sities lessthan6x10atomscm(Zombeck1982).Figure3 attenuation bygasordustislessthan1magforcolumnden- certainly originateinthecentralsource.Moreover,their arguments concerningenergyimplythathardX-raysmust nonthermal radiation,becausevariabilityobservationsand dix. Ts andextendingoverarangeofmorethan4decadesin the dataandresults(Tables2-4)arepresentedinAppen- quantities. Adetaileddescriptionofthemethodandtables performed aformalanalysisofcorrelationsbetweenthese sured atdifferentwavelengthsandinemissionlines,wehave study ingeneraltherelationbetweenluminositiesmea- class C. ferent thisbaselineisfromanypowerlawthatmightbe suggested bytherawdatafortypicalobjectsinclassBand osities aboveandbelowthebaseline.Figure1showshowdif- À, wherethebaselineisdefinedforeachobjectandlumin- circumnuclear dustordensegas.)Table1liststhewavelength, galactic dustemissioninadditiontothefromhot 598 B 2 Hereandsubsequentlyweshalluse, e.g.,[20/mi]tostandforthelumin- Figure 3showsthatthecorrelationof[3.5/un]with Further informationontheinfraredbaselinecanbe All ofthelineandcontinuumluminositiesarecorrelated The 6keVradiationisaparticularlyusefulindicatorof To examinethesignificanceofinfraredbaseline,andto b) InfraredandX-rayContinuumCorrelations © American Astronomical Society • Provided by the NASA Astrophysics Data System CARLETON ETAL. makes totheoverallenergybudget, evenwiththisconservative plot ofv/(v)emphasizeshowlarge acontributionthebigbump the poweractuallyradiatedin thatfrequencyband.Thelinear the plottedspectrum,between twovaluesoflogv,represents maximum factorof2wouldnotsignificantlychangetheresults v/(v) againstlogvisparticularly usefulinthatanareaunder of thispaper.Thepresentation ofFigure4asalinearplot than theamountshown,andevenareductionby the we consideritunlikelythattheactualultravioletfluxis less reddening istheGalacticvalueimpliedby21cmobservations, by MalkanandSargent.Consideringthatmostoftheadopted amounting to=0.17mag,comparedA0.28derived but includesamoreconservativereddeningcorrection is basedonthedataandanalysisofMalkanSargent(1982) The ultravioletportionoftheassumedcentralsourcespectrum the assumedformforunderlyingcentralsourcespectrum. sample. Figure4showstheobservationsof3C273alongwith dened spectrummightlooklikethatof3C273,awell-observed discussion thatfollows,wewillconsideratrulyunred- object thathasasmuchultravioletfluxanyin our to objectrelativethepowerlaw.Fordefinitenessin ponent, referredtoasthe“bigbump,”maychangefromobject tion disk.Thereislittleevidenceforhowmuchthiscom- index near—1.0.Manyobjectsalsoshowastrongupturnin the blue,suggestinganothercomponentinterpretedby ponent thatcanbecloselyrepresentedasapowerlawwithan Malkan andSargent(1982)asthermalemissionfromanaccre- the centralsourceluminosity. the infraredbaselineisthatX-raysaredirectlyindicativeof the keyassumptioninestablishingphysicalsignificanceof lation oftheinfraredpowerlawtoshorterwavelengths.Rather physical mechanismfortheX-rayemissionoronextrapo- (Bezier etal1984).Weemphasize,however,thatourconclu- for 3C273,wherev/(v)goesonrisingintothe100keVregion v sions regardingtheinfraredemissiondonotdependon extended fromtheinfraredandaflattercomponentthatdomi- nates athigherenergies.Thisexplanationappearssatisfactory X-ray emissionisthatitacombinationofthepowerlaw tron producingelectrons.Aplausibleexplanationofthehard emission, unsaturatedComptonizationofaninfraredsynchro- tron spectrum,andself-Comptonemissionofinfraredsynchro- models existthatcanproducesuchanextendedpowerlaw(see discussion byElvisetal1986),includingdirectsynchrotron (Madejski 1985)andisphysicallyreasonable.Severalclassesof ected quasars(Elvisetal1986)andforseveralBLLacobjects X-ray regionhasbeensuggestedforasampleofopticallysel- On theotherhand,asinglepowerlawcoveringinfraredto and thereforethepresenceofanothercomponentisindicated. this sampleareoc»0.7(Petreetal1984;Mushotzky1984), vening frequencies.Infact,themeasuredslopesinX-rayfor ily meanthatasinglepowerlawmustextendovertheinter- infrared powerlawforthissampleofobjectsdoesnotnecessar- and Table1). might beinferredfromtheclassBspectra(asshowninFig.2 spite ofthewidevariationapparentinfraredslopesthat again impliesthatourmethodofselectingIRismeaningful,in red. Second,theidentityofa_valuesfortwoclasses interesting thatthesevaluesaresoclosetotheaveragevalue a =—1.02thatcharacterizestheclassAobjectsininfra- x b IRx IR The datasuggestthatallobjectshaveanemissioncom- The factthatthe6keVpointisonanextrapolationof c) ACommonCentral-SourceSpectrum 198 7ApJ. . .318. .5 95C © American Astronomical Society • Provided by the NASA Astrophysics Data System 0.36 fimto100asafunctionofhardX-ray be classified.Thelineineachplotgoesthroughthe open squaresclassBobjects,trianglesC luminosity. FilledsquaresdenoteclassAobjects, for twoobjects(NGC4051and3C120)toindicate connected bydashedlinesinFig.3/showboth point for3C273andhasaslopeof1.Thepoints objects, andopencirclestheobjectsthatcouldnot includes somenewandstringent upperlimits IRAS andKAO(smalleraperture)measurements derived fromIRASdata(Boisson1986). Thesedata the effectofgalaxycontamination.Fig.3/also effect, (g)Theinfraredbaselineluminosity vL(v)asa function ofhardX-rayluminosity. inclusion elsewherewouldnothaveany appreciable particular relevancetotheturnover question. Their are includedonlyinthisonefigurebecause oftheir Fig. 3.—{a-f)Luminosityatwavelengthsfrom 1987ApJ. . .318. .595C turnover inthepowerlaw,butratherfallingofspec- indeed thecauseofsteeper opticalslopes.Figure5com- “equivalent width”[6keV]/L[Ha].PaperIshowedthat all would beveryinterestinginclarifyingthematter.Weempha- /¿m to100/¿m.Apower-lawturnovernearfiminsome itself showsaslightbutpossiblysignificantdownturnfrom60 central-source spectraareidenticaltothatof3C273.Inpartic- The predictedslopesderived from thereddeninglawofSavage pares thereddeningvaluesderived fromeachpairofindicators the classAnuclei.Asdefinitionofclasseswasbased three indicatorsimplymorereddeningintheclassBthan in and smalleraperturemeasurementsinthe50-150jumregion vents anyquantitativeanalysisofapossibleturnover,however, to radio-loud3C273.Theconfusionbygalacticemissionpre- radio-quiet objectsisnotsurprising,especiallyincomparison their spectraisbeginningtoturndown,particularlyas3C273 We takethisasevidencethatthepower-lawcomponentin have significantlylessfluxrelativetoX-raysthandoes3C273. ionizing photons. estimate ofitssize.Thebigbumpprobablyextendswell and Mathis(1979)arealsoshown. Mostoftheobservations slope iswell-correlatedwith each oftheothertwomeasures. and showsthatthereddening derivedfromthecontinuum only onthefirstindicator,thisisevidencethatreddening is cators ofreddening:thelineratio[Ha]/[H/f]and the good submillimeterdatawillresolvethematterdirectly. turn exhibitedbymanyspectraissimplythelow-frequency trum belowtheX-rayreferencelevel.Inourview,down- 60-100 fimthatwetaketobeevidenceforthebeginningofa size thatitisnotsimplyadownturnbetween20/miand ular, Figure3e,fshowsthatat60¿¿mand100/unmanyobjects beyond theLymanlimitandcontributesagoodshareof surements isastrongaidinmakingdistinction,although sibilities. WebelievethattheavailabilityofhardX-raymea- side ofablackbodycurvethatpeaksnear20/mi.Edelsonand 600 Malkan (1986),lackingtheX-rayreference,considerbothpos- The differencebetweenthetwoX-raymeasurementsprobablyrepresentssourcevariability.long-dashedlinedenotespower-lawbaseline,and short-dashed linerepresentsa27,000Kblackbodyspectrum.TheverticalarrowindicatestheLymanlimit(912Â). et al.(1982)andapointat1450ÂfromVéron-CettyThedottedlineshowstheX-rayspectraldistributionmeasuredbyWorrall(1979)on1978June30. [1.2 /¿m]/[0.36/mi]canbecomparedwithtwoadditionalindi- It ispresumablyanoversimplificationtoexpectthatallthe The reddeningindicatedbytheopticalcontinuumslope Fig. 4.—Theenergydistributionof3C273plottedonalinearscale.Datapointsareasin1withtheaddition6keVpoint(filledsquare)fromPiccinotti © American Astronomical Society • Provided by the NASA Astrophysics Data System a) EvidenceforReddening III. EFFECTSOFDUST lOO^m lO^xmO.l/xmO.lkeVI10 CARLETON ETAL. nificant. well withthecontinuumreddeningthatweinferfrom systems ofsixobjectsforoursample.Thesevaluescorrelate measurements aredifficultformostoftheobjectsinthislow- (Carleton etal.1984;Fabbiano1986).Unfortunately,Paa coverage ofthecentralsourcebybroad-linecloudswould give efficiency ofhydrogen-lineproductionissuchthatcomplete continuum issimilartotheoneshowninFigure4,and the spheric absorption.Lacyetal.(1982)usedtheirobservationsof redshift samplebecausethelineliesinaregionofstrongatmo- by usingPaschen-alphaintensitiesinadditiontoHaandHß continuum betweentheLymanlimitand6keV. covering factorofbroad-linegasandtheshapeionizing and Puetter1981)[6keV]/L[Ha]dependsonboththe affected byradiativetransfer(KwanandKrolik1981;Canfield nine classAobjects,including 3C273,oneclassBobject, sample, andonlyasmallfraction ofthedataareforclassB by MalkanandSargent(1982).Theimpliedcoveringfactor for the relativevaluesofv/(v)at3400ÂandLymanlimitgiven ultraviolet continuum(Neugebaueretal.1979)togetherwith based onsimultaneousmeasurementofHaandthenear- L(Ha)/[912 Â]=1/7.Theobservedratiofor3C273is 1/44 photoionization. Inthebest-fitting“standard”photoioniza- not furnishenoughultravioletphotonstogeneratethelines by limits implythatthecontinuaofclassBobjectsareconsider- lines placelowerlimitsonthefluxofionizingphotons.These Paa, Ha,andHßtoderivereddeningvaluesforthebroad-line a fewobjectsthatdisagreeisnotsurprisingbecauseHa/H/? agree reasonablywellwiththepredictions,andexistenceof objects. Véron-Cettyetal.compiled 1450Âfluxdensitiesfor tion modelofKwanandKrolik(1981),theassumedionizing ably reddenedbecausetheobservedenergydistributionsdo observed directly,theopticalandnear-ultravioletemission [1.2 /mi]/[0.36/mi],butthesubsampleistoosmalltobesig- Seyfert 1galaxiesfromIUE data. Fromoursample,theylist 3C 273isthus15%. 120, andthreeclassCobjects. Boisson(1986)hasprovidedus A bettermeasureofbroad-linereddeningmightbeobtained Ultraviolet dataexistforrelatively fewobjectsinour Although theionizingultravioletspectrumcannotbe b) UltravioletEnergyDistributions Vol. 318 1987ApJ. . .318. .595C the correlation.The linesontheHa/Hßaxesindicate thecaseBratioof each arrowisarbitrary, sothearrowsdonotrepresent theregressionlinefor indicated. Thearrowsoneachplot indicate reddeningvectorsbasedonthe Ha/Hß. reddening lawtabulatedbySavageand Mathis(1979).Thestartingpositionof tors, thesignificancePofcorrelation givenbytheSpearmanranktestis objects; thestarredpointrepresents3C 273.Foreachpairofreddeningindica- tors. FilledsquaresdenoteclassA,open squaresclassB,andtrianglesC r No. 2,1987 Fig. 5.—Thecorrelationsbetweenthree pairsofpossiblereddeningindica- © American Astronomical Society • Provided by the NASA Astrophysics Data System log [1.2/xm]/[0.36/i.m] CONTINUUM OFTYPE1SEYFERTGALAXIES.II. curve maydiffer fromtheGalacticreddening curve,because the albedoof dustparticlesmaydepend on wavelength.We for aGalacticsource.Moreover, theshapeofreddening density isneededtoproduce theindicatedvaluesofAthan contributes totheextinction. Thereforealargerdustcolumn dust iswithinourbeam,soonly absorptionandnotscattering the extinctiontoactivegalactic nuclei.Foronething,allofthe that agalacticreddeningcurve willcorrectlydescribeindetail same rangeofvisualabsorptions. their infrared-selectedsampleofSeyfertgalaxiestohave the light subtractionisessentialbeforethisstatementcanbegiven strong weight.Rowan-RobinsonandCrawford(1986) find bination ofreddened3C273plusstarlight,butaccuratestar- correct forstarlight.Figure6showsthat3C273reddened by other objectsinclassBarealsoreasonablyfittedbyacom- A =2.4isareasonablefittothespectrumofNGC931. The mined, becauseonlyone(NGC931)hassufficientdata to 0.24 isalsoshownandareasonablefittothemedianclass A spectrum. ThespectralshapeofclassBobjectsispoorlydeter- 273. Theeffectofreddeningthe3C273spectrumwithA = hard X-rayflux,togetherwiththenormalizedspectrumof3C typical Seyfert1nuclei.Figure6showsthe3.5-0.36pmportion is areasonablerepresentationoftheobservedspectrum lower frequencies. of themedianspectrumforclassAobjectsnormalizedto energy photonsdonotaffecttheionization. ior ofthespectrumbetween13.6and~30eV,higher of dustwerefartheroutandcooler,thepeakwouldappearat hot, thepeakwouldcomeinnear-IR,andifsamekind properties oftheindividualgrains.Ifdustwereclose-inand excess woulddependonthedistributionofdustand but therewouldbeadecreaseintheblueandthermalexcess that theobservedultravioletfluxdensitiesindicatebehav- v has shownexplicitlythattheline-productionefficiencyL(Ha)/ than arephotonswithenergynearthethreshold.Kwan(1986) energy photonsaremuchlessefficientationizinghydrogen ciably helptheproblemofalackionizingphotons.High- over thepowerlawininfrared.Theshapeofinfrared appear? Thefluxdensitynear1-2^mwouldbelittlechanged, spectrum isreducedrelativetotheX-rays.Thusextent manner asthenucleithathaveactuallybeenobserved. extrapolate fromtheUbandtoLymanlimitinsame violet continuumisaffectedbyextinction,whiletheionizedgas more reasonabletoassumethatourlineofsighttheultra- [912 Â]changesverylittleastheultravioletcomponentof the remainingfiveclassBobjects,providedtheirspectra sees thesourcemoredirectly.Thesameconclusionholdsfor radiation thatisundetectableat1450Â,thesevaluescertainly factor of34.Unlessthereisanadditionalsourceionizing v strain thecapacitiesofphotoionizationmodels.Itseemsmuch four oftheclassBnuclei,however,impliedcoveringfactors range from1.3to5.3,andIC4329Ahasacomputedcovering v results fortheclassAandCnucleirangefrom0.14to0.93.For flux densitiesbyassumingthatallnucleihavethesameslope then computedcoveringfactorsfromHafluxesand1450 as 3C273from1450Âthroughtheionizingcontinuum.The sured 1450Âcontinuumfluxdensitiesfromthese.Wehave NGC 3227,MGC—6-30-15,andIC4329A,wehavemea- with spectraoffouradditionalclassBobjects,MCG8-11-11, In spiteofthereasonablefit to thedata,itismostunlikely In thevisibleandnear-infrared,areddened3C273spectrum How wouldanincreasinglyreddenedversionof3C273 The presenceofahardX-raycontinuumdoesnotappre- c) DereddenedSpectralShape 601 1987ApJ. . .318. .595C emits between1and100/un(logv=12.5-14.5).Figure4 lengths ofroughly100Âand1fim(logv=14.5-16.5) noting thatdustefficientlyabsorbsenergybetweenwave- potentially availableinthethermalexcesscanbeestimatedby luminosities absorbedandreemitted.Theamountofpower in thevisibleandreradiatedinfrared,wecompare thermal excessintheinfraredcouldbemorethantwice ultraviolet asisemittedbythepowerlawininfrared,so shows thatabout2.5timesasmuchpowerisavailableinthe have usedtheGalacticreddeningcurvesimplyasafunction the visibleimpliesthatalarge amountofenergyisbeing The figureemphasizeshowmuch energy3C273emitsinthe approximation tothepower that mightbeabsorbedbydust. similarly markedareainthe ultravioletrepresentsarough resents Lfortheclass A medianspectrum,andthe lying spectrum.Thesinglyhatchedareaintheinfrared rep- that of3C273,whichwehavetakentorepresenttheunder- power lawintheseobjects. 0.7 ±0.5forclassAand2.0+1.2B.Thehigherratio of anybetteroption. that hasareasonabledependenceonwavelengthandforlack ultraviolet andshowsthateven asmallamountofreddeningin tion fromagalaxydiskandrelativelyweakernonthermal Labove/^beiow shouldapproximatetheratioofthermaltonon- luminosity aboveIR,foreachobject,andtheratio power undertheinfraredbaseline.Table1giveL,to of 3.0±1.4forclassCisconsistentwithasignificantcontribu- of theseratios,andtheirrangeisjustwhatwewouldpredict: thermal powerforeachobject.Figure7showsthedistribution matches themedian3.5/mifluxdensityforallclassBnuclei. nucleus withstarlightsubtraction,normalizedsothe3.5/mifluxdensity The pointsrepresenttheenergydistributionofNGC931,onlyclassB median energydistributionforclassAnucleinormalizedtothehardX-rays. 602 trum with0.24and2.4magofextinction{A).Thesquaresrepresentthe spectrum shiftedtotherestframe,whiletwodashedlinesshowthisspec- reddened energydistributionof3C273.Thesolidlineistheobserved273 100 /miluminositybelowIR,andLthe1to /mi above ft below v babove In ordertotestthehypothesisthatenergyisbeingabsorbed Figure 8comparesmedianspectraofclassesAandBwith Fig. 6.—ComparisonofobservedSeyfert1energydistributionswiththe © American Astronomical Society • Provided by the NASA Astrophysics Data System 3/u.m I0.3yu.m d) ThermalEmission CARLETON ETAL. objects didnotdiscriminatefororagainstdustinessapriori. sample islargelyhardX-rayselected,andthustheselectionof osity. Thepresentresultislesssubjecttoselectionbiasesasour that dustcontentofAGNsdecreaseswithincreasinglumin- consistent withtheconclusionofLawrenceandElvis(1982) excess accompaniesreddeningofthevisiblespectrum. We considertheseresultspersuasiveevidencethataninfrared ^above/^beiow isobservedinthisrange,asshownFigure9c. log [6keV]between43.5and44.3.Noluminosityeffecton luminosity nuclei.Figure9cshowsthatthereisindeedsome shows thesameplotasFigure9abutonlyforobjectswith not themajoreffect,asdemonstratedbyFigure9d,which luminosity dependenceintheexpectedsense.However,thisis relatively greaterthermalemissionofagalacticdiskforlow- reradiating itintheinfrared.Apossiblecomplicationis infrared baselineforclassA,B,andC objects. seeing theexpectedeffectsofdustinremovingUVenergyand reddening indicators.Thecorrelationbetweenthermalemis- is ameasureoftheinfluencepatchinessororientation. sion andreddeningisstrong,suggestingthatwereallyare eters areconstant.Thescatterfromthelineofbestcorrelation Figure 9a,bshowsthedependenceofL/Lontwo will begeneratediftheamountofdustvaries,butotherparam- energy remainingatthewavelengthswheredustabsorbs. shape. similar calculationsthatshowmoredetailsofthespectral median spectrumisnotimportanthere.)Anevenmoreheavily Rowan-Robinson andCrawford(1986,Fig.3d)havepresented than theclassBmedian,becausethereisnotmuchmore reddened objectcouldnotconvertagreatdealmoreenergy heavier reddening.(ThestarlightincludedintheclassB is theadditionalenergyavailableforabsorptionbecauseof doubly hatchedarea.Theultravioletcounterpartofthisexcess shows theadditionalinfraredexcessofclassBobjectsasa distributions mayhaveastronginfraredexcess.Figure8also absorbed bythedust.Thusevenobjectswithfairlyblueenergy abovebelow The smallerinfraredexcessesinhigh-luminosityobjectsare Fig. 7.—Thedistributionsoftheratio ofluminositiesaboveandbelowthe A goodcorrelationbetweeninfraredexcessandreddening NON-THERMAL «ITHERMAL m DOMINATES | I I 1987ApJ. . .318. .595C the medianclassAobject.DoublehatchingindicatesextrapowerabsorbedandreemittedforB are normalizedtothehardX-rays.Singlehatchingshowsultravioletpowerhypothesizedbeabsorbedbydustandinfraredreradiated bydustfor the filledsquaresmedianenergydistributionforclassAobjects,andopenBobjects.Alldistributions diagram. but onlyforobjectswithlog[6keV] between43.5and44.3,i.e.,objectstheverticaldashedlines in(c).Thecorrelationshown(a)isnotspoiledby class AandopensquaresBobjects, (c)Dependenceoftheratioluminosityaboveandbelowpower-law baselineonthe6keVluminosity,(d)Sameas{a) restricting thesampletoasmallrange ofluminosity.ThesignificancePeachcorrelationasmeasuredby theSpearmanranktestisgiveninappropriate r Fig. 8.—Comparisonofthepowerinferredtobethermalemissionwithavailableinultraviolet.Thecirclesrepresent3C273energydistribution, Fig. 9.—(a,b)Thecorrelationofthe ratioofinfraredluminosityaboveandbelowthepower-lawbaselinewith tworeddeningindicators.Filledsquaresdenote o CP © American Astronomical Society • Provided by the NASA Astrophysics Data System 12 13141516 100/i.m IO/aíti1/j.mO.l¿¿m log i/(Hz) 1987ApJ. . .318. .595C 44-1 -1 54 _1 44_1 lations ofKwanandKrolik(1981)togetherwiththelumin- 0.1-0.3 pcforthebroad-lineregioninferredfromcalcu- center. Thesmallestradiusaboveiscomparabletothesizeof if itisintheshadowofdustorgasthatstillcloserto class AandBobjectsisabout2x10ergs,therefore might beupto2.5timesL.Themedianvalueoffor line showsapossiblefree-freecontribution fromdenseionizedgas(Fig.lu,curve2ofPuetterandHubbard[1985]). r(45 K)ä1600pc.Cooldustmayalsoexistclosein,ofcourse, at distancesofr(1000K)æ0.7pc,r(18050and the observedemissionat3.5,20,and80fimmusttypicallyarise as 2.Asnotedin§llld,theeffectivepowerforheatingdust the dustfromsource.TheTdependenceinsteadof of theheatingsourceinergss,andrisdistancepc the dusttemperatureinkelvins,Liseffectiveluminosity agrees reasonablywellwithmoreextensivecalculations(e.g., 5 x10ergssisatypicalvalueforL.Usingthisvalue, occurs becausetheemissivityofdustwasassumedtovary Rees etal.1969;RudyandPuetter1982).Inequation(1),Tis Davidson andNetzer(1979), uncertain dustproperties.Averysimpleexpressiongivenby absorbing cloudsfromtheheatingsourceandonnecessarily 604 UBVR photometry,andthecrossisa pointat1450ÂfromVéron-Cettyetal.Thesolidlinesshowapowerlaw andasingleblackbodycurveat1050K.Thedashed dust. Thedusttemperaturedependsonboththedistanceof depends uponthetemperaturedistributionofemitting thermal infraredemission,butofcoursetheenergydistribution reddened high-luminositycasescertainlyexist(e.g.,3C234-— The sampleissmall,however,andsocontainsfewoftherare Carleton eia/.1984). radio-loud AGN.Amongradio-selectedobjects,somestrongly below eff eff Fig. 10.—The3C273energydistribution near3.5fimplottedlinearly.TrianglesdenoteIRASdata,squares denoteground-basedinfrareddata,circles So farwehavetreatedonlytheintegratedluminosityof © American Astronomical Society • Provided by the NASA Astrophysics Data System e) RadialDistributionofDust 621/5 T*1 x10~(L/r),(1) eff lOO^im 30/¿mIO^í.m3/xmI/¿m0.3/imO.l/xm CARLETON ETAL. 1-3 in the3C273spectrumthandoesfree-freeradiation. gives amuchbetterfittotheshortwavelengthsideofbump free emissioninthe3/imneighborhoodifdensitywereas for thebroademissionlinescouldgenerateconsiderablefree- peak isnotradiationfromhotdustbuttheionizedgas. pc. Onepossiblealternativeexplanationisthatthe3.5fim central-source radiationisinterceptedveryclosein,aträ0.5 sharply peaked.Figure10showsthatasingleblackbodycurve the 3.5/imbumpisthatfree-freeemissionnotvery high as10cm.Theproblemwiththisanexplanationfor at 2.3and3.5¿unthanotherwavelengths(Cutrietal.1985; components. Directevidencethatthesecomponentsare log ([IR]/[6keV])=0.23.Thusthedataareconsistentwith Robson etal.1983). occurred onatimescale~1monthwereofsmalleramplitude separate hasbeenseenin3C273,wherevariationsthat the infraredbaselineand3.5¿¿mbumpbeingindependent the ratiolog([3.5/mi]/[6keV])is0.27,whiledispersionin 273 spectrum(relativeto[IR])is0.27inlogv/(v),whilethe in classAobjects,wheretheexcessemissionnearlyalways (Neugebauer etal.1979).The3.5/unpeakisverywelldefined (Rieke andLebofsky1981)evenoccursin3C273 3.5 jum.ThisbumphasbeenpreviouslynotedforNGC4151 average overtheentiresampleis0.29±0.19.Thedispersionin decreases from3.5jamto5or10/¿m.Itsamplitudeinthe3C correspond totheinnerpartofagalacticdisk. Puetter andHubbard(1985)showedthatthegasresponsible perature andradiusabove.Thethirdtemperature give aradiusof30-300pc,correspondingtothesecondtem- narrow-line region(Ferland1981)andthesameluminosity osity assumedabove.Calculationsforthesizeof & & If the3.5fimbumpisduetodust,asignificantfractionof Many objectsshowapronouncedbumpinthespectrumat Vol. 318 1987ApJ. . .318. .595C /mi]). Thetotal“thermalluminosity,”L,islesswelllinked source. factors of~5000inradiusif the centralsourceisonlyheat grows relativetothehotdustemission(i.e.,high[20/mi]/[3.5 dominant, (i.e.,high[Om]/Ha),thecoolerdustemission that Lintegratesemissionfromdustcoveringafactor of with L([0m])thanis[20/mi].Tnissimplyreflectsthe fact this, showingthatasthenarrow-lineregionbecomesmore these effects,thescatterismuchreduced.Figure12illustrates If, however,oneformsasecondratiothatisindependent of and ionizationwouldaddconsiderablescattertotherelation. gas-to-dust ratiosorintherelativeefficiencyofdustheating It istoomuchtoexpect[Om]and[20/mi]orHa and with L([0in]),while[20/mi]correlatesbetter m]). which showsthat[3.5/mi]correlatesbetterwithL(Ha)than ment withourcorrelationanalysis(Tables3and4;Fig.13b,c), emission andbetween[Om]and,say,20jam.Thisisinagree- [3.5 /mi]tobeuniquelycorrelated,becausedifferencesin the that thereshouldbeacloseconnectionbetweenHaand3.5/un tances ofthebroad-linegasandnarrow-linesuggest separate distances,theexpecteddusttemperaturesatdis- above nuclei. (which mayincludeburstsofstarformation)ratherthanfrom most oftheemissionfromthesecamegalacticdisks ~30 intemperature.Thisdust mustbephysicallyspreadby above original samplewasinclassC,andPaperIgaveevidencethat emission, andtheobjectswithmuchdustinthisrangewould be placedinclassC.Nevertheless,onlyasmallfractionofthe Such dustwould,ofcourse,appearthesameasgalacticdisk the energyisinterceptedatdistancesinkiloparsecrange. sion at60to100jam,suggestingthatnoappreciableamountof object. either case,theamountofdustinourlinesightisnotneces- sarily proportionaltotheamountofdustsurrounding random patchinessortosystematicorientationeffects.In correlations arepoorer,butthetrendsinrightdirec- tion. Thescatterinthesediagramsmaybeassignedeitherto the samedustthatreddensbroademissionlines.Theother rement (Fig.114implyingthatthedustradiatingat10jumis The 10fimexcesscorrelatessurprisinglywellwithBalmerdec- shows thecorrelationof10and20/onexcesseswithreddening. have bigbumpsevenlargerthanthatof3C273.Figure11c-/ factor wouldbereducedonlyiftheintrinsicsourcespectra including mostoftheclassBobjects.Theimpliedcovering and absorptionindicatedinFiguredimplythatthecovering factor ofthisdustmustbequitesubstantialinsomecases, the dustisdirectlyexposedtocentralsourceorcloserif lengths implythattheradiatingdustliesmostlyatr^50pcif most ofthedustisshadowed.Therelativeamountsemission red excessesoccuratwavelengthsof10to25/un.Thesewave- from dustinornearthebroad-lineregion. with thesuggestionthat3.5/unbumpcouldbeemission No. 2,1987 general increasingtrendisevident.Thisresultconsistent Figure 11a,b.Thereiscertainlyconsiderablescatter,buta reddening. Theresultfortworeddeningindicatorsisshownin compare theexcess3.5jumemissionwithamountof Our analysisofthecontinua of Seyfert1nucleiisuniquein If dustinAGNsisactuallyconcentratedwiththegasattwo Finally, themedianspectradonotshowmuchexcessemis- The medianspectrainFigure8showthatthelargestinfra- A testofwhetherthe3.5/imbumpisduetodust © American Astronomical Society • Provided by the NASA Astrophysics Data System IV. COMPARISONWITHOTHER MODELS CONTINUUM OFTYPE1SEYFERTGALAXIES.II. have hadlittlesuccess(e.g., Roche etal.1984;Aitkenand detection ofdustspectralfeatures inemission.Searchessofar Roche 1985;Moorwood1986). However,failuretodetectfea- important inunbiasedsamples. -1 biased againstdustcontent(Rudy 1984),itmustbeevenmore make aconsiderablecontributiontotheinfraredemission. If absorption andthermalemissionisfoundeveninsamples tion occursataverylargedistancefromthenucleus,dustmust energy emittedintheultravioletshouldbeabsorbedby dust and reemittedsomewhereintheinfrared.Unlessabsorp- A ä0.2foundbyEM)implythatmorethanhalfof the absorption generallyconcededtobepresent(e.g.,themedian infrared emissionisentirelynonthermal,withnothermalemis- sion fromdustatall.Eventhemodestamountsofvisual EM areprobablybiasedtowardlowreddening(e.g.,Rudy and Illh).Moreover,thesamplesstudiedbyMacAlpine and Fabbiano etal.1986;Carleton1984;thiswork,§§Illa of largerreddeninginsomeobjects(A~1.5,Lacyetal1982; required byEM(MacAlpine1985;EM),thereisalsoevidence continuum reddeningatthefewtenthsmagnitudelevel determined. Althoughthereiscertainlyevidenceoflineand 1984). sion lines,butitisreallythecontinuumreddeningthatmustbe values forotherSeyfertl’sandQSOswithsteepspectra. the onlyoneofourclassBobjectsintheirsample,andsimilar responding toA>2,whileEMderive=0.3for3C120, v have suggestedthattheobjectsinclassBreddeningcor- cussed above,andwediscusspossibledirecttestsbelow.We the differentinfraredemissionmechanismshavebeendis- tinua havetwodifferencesthataredirectlytestable.Those thermal ornonthermal.Statisticalteststodistinguishbetween the amountofreddeningandwhetherinfraredemissionis better withhardX-rays. is littlecontaminatedbyothercomponents(nucleardust,star- being abetterrepresentationofthepowerlaw,correlateseven light, cooldustinthegalaxydisk).ThelowestvL(v)point, ponent. Theonlyspecialpropertyofthe3.5/mipointisthatit power lawequallywellrepresentstheluminosityinthatcom- v fixed slopeunderliestheinfraredspectrum,anypointon fim point.Bycontrast,inourpicturewhereapowerlawof unless forsomereasonthepower-law“pivots”about3.5 ent slope,the3.5/miluminosityrepresentsadifferentsampling of thebolometricluminosityinpowerlaweachgalaxy, continuum isthatitdoesnotpredictthegoodcorrelation v between [3.5jum]and[6keV].Aseachspectrumhasadiffer- parison withtheirworkisagoodmeansofsummarizingour analysis withemphasisonthefeaturesthatareparticulartoit. amplitudes toaccountforthecontinuumradiation.Acom- variable slopeplusadditionalcomponentswith effects ofdust.Theypostulateapower-lawcomponentwith uum ofobjectssuchasthesewithminimalrecoursetothe been takenbyEM,whotrytoexplainthe0.1-100/micontin- and subsequentthermalreradiation.Adifferentapproachhas tional physicalprocess:theabsorptionofradiationbydust central source,scaledonlyinluminosity,andasingleaddi- The dusthypothesisexplainsallthedatawithasingletypeof infrared andascribealldeparturesfromittotheeffectsofdust. that wepostulateauniversalvpower-lawcontinuuminthe The mostdirectevidencefor dustemissionwouldbethe There isafundamentaldifficultywithanyassertionthatthe The reddeningcanbemeasuredmosteasilyfromtheemis- The dusthypothesisandtheEMofdiversecon- One difficultywiththeEMinterpretationofinfrared 605 1987ApJ. . .318. .595C The probabilitiesPthatthecorrelationscouldarisebychance(basedon a Spearmanranktest)aregivenineachframe,{a,b)-3.5d)-10fim;(e,f)-20/mi. denote classAandopensquaresBobjects.Thequantityplottedishypothesized torepresenttheratioofthermalnonthermalluminosityateachwavelength. r Fig. 11.—Ratioofluminositiesaboveandbelowthepower-lawbaseline atindividualwavelengthscorrelatedwithtworeddeningindicators.Filledsquares T m a: io O o tr E © American Astronomical Society • Provided by the NASA Astrophysics Data System E xt i .o Xi 3- 2- I - _ P=0.003 r —^ \r -0.4 J »JI log [1.2/i.m]/[0.36/im] ■ 0.4 0.81.2 “I I a) log L(Ha)/L(H/3) 1987ApJ. . .318. .595C broad emission-lineregions.Thedustcontributionsaretakentobetheexcessesaboveinfraredbaselineat3.5and20/¿m,respectively.Solidsquares denoteclass A objects,opensquaresdenoteclassBandtrianglesCobjects.Thecorrelationsignificanceisindicated. ing toAæ2fortheobjects with thesteepestopticalspectra. It wouldbeinterestingtoexamine othersamplesthatare plausible way.Wededuceacontinuum reddeningcorrespond- relations amongtheobservedquantitiesinasimple,physically X-ray emittingsample.Thedusthypothesisexplainsnumerous existing observationsofvariability(LebofskyandRieke1980; include thepresenceandcharacterofvariability(Reesetal cally thickclouds,orlesssilicaterichgrainswouldallweaken is notyetpracticalbutverysoonwillbecomeso. consistent withthermalemissionbutfarfromconclusive(Rudy et al.1982).Directmeasurementofsourcesizesintheinfrared definitive test.Multiwavelengthpolarizationstudiesarealso thermal emission,buttherearetoofewobservationsfora nated bydustemission(Rieke1985;EM). the factthatthosenucleiaregenerallyconsideredtobedomi- smooth spectra,andnoneshowssilicateemission,inspiteof the dustfeatures.Indeed,Seyfert2nucleigenerallyshow different inactivenuclei.Largegrainsizes,thickmantles,opti- depend stronglyondustpropertieswhichmaywellbevery good fractionoftheinfraredcontinuum,asthesefeatures tures countsonlyveryweaklyagainstathermaloriginfor weaker inhardX-raystosee ifthesameinterpretationis single spectrumisconsistentwithallofthedataforourhard tinua undoubtedlydifferinsomedegree,theassumption of a and thermalreemission.Whiletheunderlyingnonthermalcon- observed spectrumof3C273togetherwithdustabsorption understood asasingleunderlyingspectrumsimilarto the contributions iscorrect,most oftheabsorptioncentral viable. Rieke andLebofsky1979,1981;Cutrietal.1985)favor 1969), polarimetry,andmeasurementofsourcesize.Most v We suggestthatthecontinuaofSeyfert1nucleimaybe Other teststodistinguishthermalfromnonthermalemission If thepictureofidenticalcentral sourceswithdifferentdust Fig. 12.—Correlationoftherationarrowtobroademissionlineswithinfraredexcessesduedustinferredbeatdistances narrowand © American Astronomical Society • Provided by the NASA Astrophysics Data System V. CONCLUSIONS _ -0.6- a o _J x ö « -0.2- o -0.8- C7> -0.4 - -1.2 - -1.4 - 0.4 - 0.2- -0.8 -0.6-0.4-0.200.20.40.60.8I 0 - CONTINUUM OFTYPE1SEYFERTGALAXIES.II. P< 0.0005 r n 1r log ([zOfjLm]-[lR])/([3.5^m]-[lR]) b explanation oftheinfraredandvisiblecontinua. extremely valuable,thoughdifficulttoobtain. in thefar-infraredandsubmillimeterregionswouldbe made inthevisibleandnear-infrared.Smallbeamobservations contributions fromstarlightandcooldust.Thisempha- windows tothecentralnonthermalcontinuumarebetween1 contribution fromdustemission,andthemostreliable broad-line region.Mostinfraredwavelengthscontainsome distances correspondingtotheregionwherenarrowemis- /¿m andshorterwavelengthssimultaneously.Totheextent that sizes thenecessityofsubtractingstarlightfromobservations unfortunately justtheregionswherehostgalaxyhaslarge and 2/unatwavelengthslongerthan100/tm.Theseare that canbeunderstoodasdustatdistancestypicalofthe sion linesareformed.Thereisalsoanemissioncomponent source radiationandthermalreemissionbydusttakesplaceat “ reasonable”dustcompositionandaboutthegeometry, this bination ofdustcomposition,temperaturedistribution, and spectrum canbereproducedwithsomereasonablecom- this hasbeendone,evidencefavorsourmodel. emission isnonthermal,thenuclei shouldbeverysmall,while reddening hypothesis. hypothesis withthemuchlargerfluxesimpliedby the the reducedultravioletfluxesimpliedbysteepcontinuum ses. approach maynotyieldacleardistinctionbetweenhypothe- optical depth.Asweareuncertainabouttherange of emitting gas. diameter. Comparisonofinfrared andemission-lineimages thermal emissionshouldcome fromregionsoforder100pcin should indicatewhetherdust isdirectlyassociatedwithline- There areseveralareasoffutureworksuggestedbyour 4. Obtainhigh-resolutionimages at10and20/¿m.Ifthe 2. Investigatewhethertheobserveddetailsof8-13/un 3. Constructemission-linemodelstocomparetheeffectsof 1. Monitorvariabilityofsteep-spectrumobjectsat10-20 1.2 1.4 607 1987ApJ. . .318. .595C Table 2givesacompilationofallthecontinuumandemission-lineluminositiesusedincorrelationanalysis. 3givesthe sample. Tokeeptheamountofinformationmanageable,wewillusefollowingdata. advance ofpublication,E.H.Avrettforvaluablediscussions, modeling thegenerationofX-rayspectrum. thermal andnonthermalcomponentsinthisregion of thenonthermalspectrum.Thiswouldassistinseparating observations soastodefinebetterthepossibleturnoverregion 608 3 3 4. [20¿mi],torepresenttheinfraredregionmostlikelybecontaminatedbywarm-dustemission. Forbroad-lineobjects,thisistheluminosityinbroadcomponent.narrow-linegalaxiesNGC2992and5506,totalHa wasused. 7. L,(discussedin§Illfr)torepresentapossiblemeasureofthermaldustemissionabovetheinfraredbaseline[IR ]. 6. [IRJ,(thelowestpointinthe1.2-100fimrange)torepresentapossibleinfrared“window”oncentral-sourcecontinuum. 5. [3.5¿mi],torepresentthesameforhot-dustemission. 2. L(Ha),torepresentgasinthebroad-lineregion. 3. L([0m]),torepresentgasinthelargerforbidden-lineregion. We presenthereaformalanalysisofcorrelationsbetweensomethelineandcontinuumluminositiesforobjectsinour The authorsthankC.Boissonforcommunicatingdatain 1. [6keV],torepresentthecentralsourcecontinuum. above fe 5. Obtainsmalleraperturefar-infraredandsubmillimeter © American Astronomical Society • Provided by the NASA Astrophysics Data System (d) Phillips1979;(e)Wilsonetal.1976; (/)Phillipsetal.I979;(g)Ward1980;(h)Yee1980. NGC 7213 NGC 7469 NGC 7314 NGC 7172 NGC 4593 NGC 4051 NGC 3227 NGC 2992 ESO 103-G35 NGC 5506 MCG-6-30-15 MCG-8-11-11 NGC 931 NGC 526a 3A 0557-385 Class C: 3C120 Mkn 509 ES0 141-655 Mkn 841 Mkn 1383 NGC 5548 IC 4329A NGC 4151 NGC 3783 Mkn 79 Ákn 120 Class B: F-9 3C273 Class A: III Zw2 Obj ect References forHaand[Om]:(a)Rudy 1984;(b)Neugebaueretal.1979;(c)Ward(unpublisheddata); CONTINUUM ANDEMISSION-LINECORRELATION Continuum andLineLuminositiesUsedinCorrelationAnalysis [6 keV][3.5pm][20pm] 42.48 43.46 42.51 43.01 42.80 41.27 41.95 43.09 42.79 43.63 43.12 42.95 44.14 43.53 44.10 43.24 43.61 44.25 44.16 43.88 44.27 43.69 45.79 42.74 43.01 43.64 43.80 44.26 44.95 43.17 44.22 42.41 43.59 43.42 42.18 42.45 43.25 43.47 44.24 43.29 43.04 44.74 44.06 44.55 44.01 43.73 44.60 44.51 44.21 43.96 46.15 43.14 43.64 44.04 44.46 44.99 45.03 CARLETON ETAL. APPENDIX 44.72 43.30 42.46 42.94 43.53 43.54 44.45 43.39 44.58 44.60 44.52 44.16 44.72 44.49 43.97 44.24 46.04 43.39 43.82 44.25 TABLE 2 colleague whomwegreatlyvaluedforhisintellectand brightness andgoodcheer. work inastrophysicsonlyjustbegun,hastakenfromusa extensive, high-qualityobservationalworkofDr.Christopher useful conversations.Dr.McAlary’suntimelydeath,withhis W. McAlary,withwhomwehavehadmanyinterestingand and A.W.Campbellforhelpfulcommentsonthemanuscript. This paperanditscompaniondependstronglyuponthe 42.36 43.11 44.08 43.16 43.23 42.01 42.33 42.97 43.27 43.23 43.59 44.18 42.90 43.63 44.12 43.50 43.60 44.35 44.27 43.98 44.78 43.78 45.97 42.89 43.20 43.75 44.18 44.85 44.83 [IRbi 42.78 41.3 41.78 40.30 40.25 41.31 41.36 40.73 42.71 41.24 42.53 43.09 41.91 41.84 43.44 43.36 43.16 42.67 44.84 41.85 42.07 42.74 43.77 43.81 43.37 L(Ha) L([OIII])(ref) 42.11 40.78 40.88 40.10 40.55 41.39 41.69 41.56 40.92 40.52 42.22 42.43 41.42 41.74 42.52 42.37 42.36 43.58 41.98 41.86 41.82 42.92 41.95 42.02 42.56 (a) (d) (a) (a) (a) (g) (f) (e) (a) (a) (a) (a) (c) (c) (a) (a) (a) (b) (a) (h) (a) (a) (a) (a) (a) Vol. 318 1987ApJ. . .318. .595C No. 2,1987 line, andthenumberofobjectsinthirdline. results fromperforminganonparametricSpearmanrankcorrelationtestonallthepairsofvariables.Foreachcorrelation, the X-ray continuum(between912 Âand6keV)areimportant. with [6keV]isexpected.The lackofsuchacorrelationsuggeststhatvariationcovering factorandvariationsinthefarUV/soft where alltheemissionlinesarise fromphotoionizationbythecentralUV/X-raysource, astronganddirectcorrelationofL([0m]) entire sampleandfortheobtainedbyexcluding “galaxydominated”classCgalaxies.(SeePaperI.)Wehavenotapplied correlations areintrinsicallyvalid,andwhichmaybethe secondary resultsofotherprimarycorrelations?Thesequestionscanbe one-tailed probabilitythatthecorrelationmightarisebychanceisgiveninfirstline,coefficients inthesecond variable. L([0 in])and[20pm]isdifferent whenthiscorrelationistestedrelativetotheL(Ha)and [3.5pm]variablesorrelativetotheL set ofvariableschosen,asforanychoiceitisalways possiblethatthecorrelationsunderexaminationareaconsequence resulting probabilities,andtherelationsamongsomeof variablesareshowngraphicallyinFigure13.Giventheintrinsicnature this testtoclassAgalaxiesalonebecausethenumberofobjects detectedinallthevariablesisgenerallytoosmall.Table4lists three ormorewhentheothervariablesarekeptfixed.We haveappliedthistesttogroupsofthreeorfourvariablesbothforthe partial correlationcoefficients,whichrepresenttheconditional probabilitiesofcorrelationsbetweentwovariablesinagroup astrophysics seeMacklin1982;Tananbaumetal.1983;Fabbiano etal.1984;andFabbianoTrinchieri1985).Thetestgives answered withtheSpearmanpartialrankcorrelationtest (KendallandStuart1979;forpreviousapplicationsofthistestin pm luminosityisthereforealsounlikely.Moreoverthecorrelationsarepresent,althoughtoalesserdegree,in relationships which areavailableformostofthegalaxiesinsample.Thepresenceadominantdistancebiascorrelations withthe20 galaxies wereobservedanddetectedat3.5/un.Asfluxwasnotanaprioriselectionthisfrequency,wecanexclude thepossibility of alinkwithsomevariablenotconsidered.Thisexplains, forexample,whytheformalconditionalprobabilityofalinkbetween of partialcorrelationanalysis(seeKendallandStuart1979), theconfidenceofacorrelationbetweentwovariablesdependsupon between thefluxes. that the3.5pmtoX-raycorrelationresultsfromadistancebias.Thesameistrueforcorrelationswithline luminosities, above The observedcorrelationsarenotlikelytobedueaselectionbias.Althoughoursampleisflux-limitedinthe X-rays,all One resultofourcorrelation analysisisthelackofastrongconnectionbetween[6keV] andL([0m])(Fig.13d).Inapicture Having establishedcorrelationsofinfraredwithotheremission parameters,weraisethequestion:which,ifany,ofthese © American Astronomical Society • Provided by the NASA Astrophysics Data System would showacorrelationcoefficientashighr. 3 b L(Ha) ^above L([0 III]) [3.5fim] [6 keV] [IRb] [20fim] QuantitiestoupperrightofdiagonalareforclassAandBobjects,whilequantitieslowerleftonly. ValuesintablearethenumberofobjectsN,correlationcoefficientr,andprobabilityPthatrandomobservations -6 =5xl0 -8x10-4 -5x10-7 <5xl0“7 -7x10-6 [6 keV] <5x10-7 0.982 0.976 0.972 0.933 0.964 0.936 N*> b 11 rb 12 11 11 P 8 9 CONTINUUM OFTYPE1SEYFERTGALAXIES.II. «5x10-7 -5x10-6 -7x10-5 <5x10-7 -7x10-5 <5x10-7 [3.Sum] 0.946 0.982 0.976 0.991 0.952 0.909 20 11 11 11 8 9 3 Spearman RankCorrelationResults -5x10-5 <5x10-7 -5x10-6 -8x10-5 [20jim] -5x10-6 0.854 0.924 0.952 0.976 0.976 0.833 8x10-3 15 15 8 8 8 TABLE 3 «5x10-7 -5x10-5 -8x10-4 <5x10-7 [iRbl -7x10-5 <5x10-7 0.981 0.936 0.846 0.973 0.900 0.909 21 20 13 11 11 9 ^above -7x10-5 -2x10-4 -4x10-4 <1x10-6 <5x10-7 0.752 0.884 0.955 0.741 0.917 0.850 2x10-3 18 18 15 18 9 9 -1x10-5 <5x10-7 -5x10-4 <5x10-7 <5x10-7 -8x10-6 L(Ha) L([0III]) 0.937 0.858 0.836 0.928 0.709 0.900 19 19 14 19 17 11 -8x10-7 -1x10-6 -2x10-4 -5x10-7 -2x10-3 <5x10-7 0.940 0.840 0.801 0.861 0.666 0.902 19 19 19 14 19 17 609 1987ApJ. . .318. .595C Kwan, J.1986,Ap.J.,305,679. Kendall, M.,andStuart,A.1979,The AdvancedTheoryofStatistics,Vol.2, Edelson, R.A.,andMalkan,M.A.1986,Ap.J.,308,59(EM). Davidson, K.,andNetzer,H.1979,Rev.Mod.Phys.,51,715. Cutrie, R.M.,Wisniewski,W.Z.,Rieke,G.H.,andLebofsky,M.J.1985, Ap. Ferland, G.J.1981,Ap.J.,249,17. Fabbiano, G.,Willner,S.P.,Carleton, N.P.,andElvis,M.1986,Ap.J. Fabbiano, G.,andTrinchieri,G.1985, Ap.J.,296,430. Fabbiano, G.,Miller,L.,Trinchieri, Longair,M.andElvis,1984,Ap.J., Elvis, M.,Green,R.F.,Bechtold,J.,Schmidt,Neugebauer,G.,Soifer, B. T., Carleton, N.P.,Willner,S.Rudy,R.J.,andTokunaga,A.T.1984,Ap. J., Canfield, R.C,andPuetter,C.1981,Ap.J.,243,390. Aitken, D.,andRoche,P.F.1985,M.N.R.A.S.,213,111. Boisson, C.1986,privatecommunication. Bezier, M.,Kendziora,E.,Staubert,R.,Hasinger,G.,Peitsch,W.,Reppin, C, the correlationisinsignificant.Thenumberofobjectsincludedineachtestwrittenunderneathrelateddiagram. associated witheachmarkingaregiveninthelegendandrangefromP0.005foratriplelineto<4%dottedline;absenceof lineindicatesthat fixed. Quantitiesconnectedbymultiplelinesarethemostcloselyrelated,andtheserelationstakentobeintrinsicallysignificant.Theformal probabilities and Bobjectsonly.Theresultsindicatetheconditionalprobabilityofcorrelationbetweenanytwovariablesinagroupthreeormorewhen othersarekept random 610 Values Correlated b: L(Hct),L([0III]),[20|iin],[3.5^m] a: [6keV],[3.5nm],[IR] d: [6keV],L(Ha),L([0III]) c: L[0III]«[20|im],^above b a b (4th ed,;London:CharlesGriffin),chap. 27. (Letters), 304,L31. 277,115. J., 296,423. 284,523. Trümper, J.,andVages,W.1984,Astr.Ap.,136,351. Matthews, K.,andFabbiano,G.1986,Ap.J.,310,291. L Fig. 13.—SummaryoftheresultsSpearmanpartialrankcorrelationtest(Table4).Theleftcolumnisforallobjects,whilerightincludes classA Correlationcoefficient. Probabilityofrandomdatabeingthiswell-correlated. L(Ha), L([OIII] L( [OIII]),[S.Sfim] L( [0111]),[20im] L(Ha), [3.5^m] L(Ha), [20iun] above. L([OIII]) L( [OIII]),[201«»] L(Ha), L([OIII]) L( [OIII]),[6keV] [IRb], [6keV] [3.5fim], [IR] [6 keV],[3.5urn] [20|iin], [3.5iim] [20|un], L [6 keV],L(Ha) b above © American Astronomical Society • Provided by the NASA Astrophysics Data System Spearman RankPartialCorrelationResults -0.534 -0.426 -0.244 0.600 0.587 0.257 0.721 0.625 0.947 0.684 0.564 0.654 0.741 0.648 0.087 a All Objects D Pb (28 objects) (19 objects) (18 objects) (25 objects) TABLE 4 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 0.099 0.045 0.009 0.195 0.015 0.345 Class AandBonly -0.505 -0.480 -0.596 0.846 0.115 0.404 0.596 0.641 0.840 0.782 0.953 0.763 0.749 0.069 0.545 pa Pb (20 objects) (14 objects) (14 objects) (19 objects) CARLETON ETAL. <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 0.320 0.045 0.048 0.022 0.059 0.013 0.017 0.010 0.394 REFERENCES Neugebauer, G.,Oke,J.,Becklin,E.E., andMatthews,K.1979,Ap.J.,230,79. 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