The infrared is a key wavelength regime for probing the dusty, obscured nuclear regions of active galaxies. We present results from an infrared study of 87 nearby Seyfert galaxies using the Spitzer Space Telescope and ground-based telescopes. Combining det

Buchananetal.:SeyfertIRSEDs283

2.SeyfertInfraredSEDs

Thesampleofobjectsstudiedcomprisesthe85Seyfertgalaxiesfromtheextended12µmsam-ple(Rushetal.1993)withcz<10000kms 1,excludingtwosourcesduetoproblemswiththedata.Thepropertiesofthesamplearediscussedinmoredetailin(Buchananetal.2006)andBaumetal.(2008,inpreparation).TheSpitzerSEDscoverthewavelengthrange3.6–100µm,andcompriseIRACphotometryat3.6,4.5,5.8and8.0µm,IRSlow-resolutionspectroscopyfrom5–35µm,andMIPSSED-modespectrafrom～50–100µm.Inaddition,near-IRphotometrymeasuredusingUKIRTwasusedtoconstructhigherspatialresolutionSEDsfrom～1–4µmfor40%ofthesample.ExampleSpitzerSEDsareshowninFigure1.

TheSEDsweredecomposedintostarburstandAGNcontributionstothedustheating(Gallimoreetal.2007andGallimoreetal.2008,inpreparation)by ttingthecombinationofaclumpytorus(Nenkova,Ivezi´c&Elitzur2002)andastar-burstmodel(Siebenmorgen&Kr¨ugel2007).SEDdecompositionsforthesourcesshowninFigure1areshowninFigure2.

We ndthattheSeyfert1stendtoshowweaksilicateemission,whiletheSeyfert2sshowsomewhatstrongersilicateinabsorption.Thisisconsistentwiththeuni edschemeforAGN.Thesamplecontainsseveral‘anoma-lous’sources,includingSy1swithsilicateinabsorption,Sy2swithsilicateinemissionandsilicateabsorptionat9.7µmbutemissionat18µm.Thesefeaturescanbeaccountedforbytheclumpytorusmodelbutnotbysmooth-densitytorusmodels,providingstrongsupportfortheclumpytorusmodel.

HiddenSeyfert1s(opticallyidenti edSeyfert2swithahiddenbroadlineregion(HBLR)observedintheinfraredorpolarisedlight)closelyresembleSeyfert1galaxiesintheirinfraredSEDs.Thisprovidesfurthersup-portforthehypothesisoftheuni edscheme,thattype1and2AGNscontainthesamesortofcentralengine.

We ndthattheSeyfert1sandtheSeyfert2swithknownhiddenbroadlineregionsaregenerallyAGN-dominatedat12µm,whilethe

Seyfert2swithoutHBLRtendtobestarburst-dominated.Thisislikelytobeaselectionef-fectinthesampleduetothemildanisotropy(aboutafactorof2)ofthemid-IRemis-sionandtheselectionofthesampleat12µm(Buchananetal.2006).

Spectralindicesinthemid-IR(20-30µm)andfar-IR(50-90µm)weremeasured,toesti-matetherelativecontributionsofcooldust.Inaddition,lineandcontinuumdiagnosticsweremeasuredusingPAHFIT(Smithetal.2007).Figure3showsthatthePAH6.2µmequiv-alentwidthiscorrelatedwithwiththemid-andfar-IRspectralindices.ThefactthatthePAHemissionisstrongerinsourceswithalargercooldustcontribution(redderspectralindices)arguesthatthecooldustisprimarilyheatedbystarformationandnottheactivenu-cleus.WealsonotethattheSy2swithhid-denbroadlineregionsshowweakerstarforma-tion(weakerPAHemission)thanthosewith-outhiddenbroadlineregions,suggestingthatthebroadlineregionismoredi culttode-tectinthepresenceofmorestarformation.CorrelationsbetweenAGNandstarbursttrac-ershavebeenfoundforQSOsandSeyferts(e.g.,Haasetal.2003;Maiolinoetal.2007).Figure4showstheobservedcorrelationbe-tweenthe6.2µmPAHluminosityandthe[NeV]24µmluminosityforoursample.Itisnotclearifthisapparentcorrelationisduetofeedbackorissimplythatthebothpropertiesrelatedirectlytotheavailablesupplyofmolec-ulargas.

Thenear-IRSEDsweredecomposedintostellarandhotdustcomponentsusingasim-plenon-AGN+blackbodymodel,wherethenon-AGNSEDwasderivedfromthecoloursofnon-Seyfertgalaxiesinthe12µmsampleofgalaxies(Spinoglioetal.1995)andthetem-peratureoftheblackbodywasallowedtovary.We ndthatthedusttemperaturesweretypi-cally～1000K,somewhatcoolerthanthedustsublimationtemperature.Figure5showsthefractionalcontributiontotheemissionbythehotdustcomponentasafunctionofwave-length.We ndthattheAGNcontributionincreaseswithwavelengthanddominatesby3.7µm.TheSy1sshowslightlylargerhotdust