Optical–to–X-ray emission in low-absorption AGN: Results from the Swift-BAT 9 month catalogue

25 Pages·2009·1.75 MB·English

Mon.Not.R.Astron.Soc.000,000–000(0000) Printed15July2009 (MNLATEXstylefilev2.2)
Optical–to–X-ray emission in low-absorption AGN: Results from the
Swift-BAT 9 month catalogue
1 2 3 1
R. V. Vasudevan R. F. Mushotzky , L. M. Winter and A.C. Fabian
1InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA
9 2LaboratoryforHighEnergyAstrophysics,NASA/GSFC,Greenbelt,MD20771,USA
0 3CenterforAstrophysicsandSpaceAstronomy,UniversityofColoradoatBoulder,440UCB,Boulder,CO80309-0440,USA
0
2

l 15July2009
u
J

4
ABSTRACT
1
Wepresentsimultaneousoptical–to–X-rayspectralenergydistributions(SEDs)fromSwift’s

X-ray and UV–optical telescopes (XRT and UVOT) for a well-selected sample of 26 low-
]
E redshift(z < 0.1)activegalacticnuclei(AGN)fromtheSwift/BurstAlertTelescope(BAT)
H 9-monthcatalogue,thelargestwell-studied,hardX-rayselectedsurveyoflocalAGNtodate.
. OursubsampleconsistsofAGNwithlowintrinsicX-rayabsorption(NH < 1022cm−2)and
h minimalspectralcomplexity,tomoreaccuratelyrecovertheintrinsicaccretionluminosityin
p thesesources.WeperformacorrectionforhostgalaxycontaminationinallavailableUVOT
-
filter images to recover the intrinsic AGN emission, and estimate intrinsic dust extinction
o
r from the resultant nuclear SEDs. Black hole mass estimates are determined from the host-
t galaxy2MASSK-bandbulgeluminosity.AccretionratesdeterminedfromourSEDsareon
s
a averagelow(EddingtonratiosλEdd . 0.1)andhardX-raybolometriccorrectionsclusterat
[ ∼10–20,incontrastwiththehighervaluesseenforquasars.AnaverageSEDforthe22low

1 accretionrate(λEdd < 0.1)objectsispresented,withandwithoutcorrectionforextinction.
v SignificantdustreddeningisfoundinsomeobjectsdespitetheselectionoflowNH objects,
2 emphasisingthecomplexrelationshipbetweenthesetwotypesofabsorption.Wedonotfind
7 acorrelationofoptical–to–X-rayspectralindexwithEddingtonratio,regardlessoftheoptical
2 referencewavelengthchosenfordefiningthespectralindex.Ananti-correlationofbolomet-
2 ric correctionwith black holemass may reinforce‘cosmic downsizing’scenarios, since the
. higher bolometric correctionsat low mass would boost accretion rates in local, lower mass
7
0 black holes. We also performa basic analysis of the UVOT-derivedhost galaxycoloursfor
9 our sample and find hosts cluster near the ‘green valley’ of the colour-magnitudediagram,
0 but better quality images are needed for a more definitive analysis. The low accretion rates
: andbolometriccorrectionsfoundforthisrepresentativelow-redshiftsampleareofparticular
v
importanceforstudiesofAGNaccretionhistory.
i
X
Keywords: blackholephysics–galaxies:active–galaxies:Seyfert
r
a
1 INTRODUCTION resultstoidentifytrendsbetweendifferentSEDparameters.How-
ever,recoveringthetrueaccretionluminositycanbecomplex,and
Active Galactic Nuclei (AGN) are known to emit radiation over previous studies have found a wide spread in the conversion fac-
thewholerangeofavailableenergiesobservableusingcurrentde- tors(bolometriccorrections)betweentheX-rayluminosityandthe
tectors. Characterising their spectral energy distribution (SED) is totalaccretionluminosity.Thisis,inalargepart,duetointrinsic
therefore important for understanding the different physical pro- variationbetweenobjectsinthewholeAGNpopulation,butisalso
cessesatwork.Theacceptedparadigmbehindtheradiationoutput complicated by numerous systematics and biases in the samples
ofAGNisaccretionontoasupermassiveblackhole.Theemission used.
directlyduetoaccretionemergesprimarilyintheoptical,UVand The pioneering study of Elvisetal. (1994) (hereafter E94)
X-rayregimesbyacombinationofthermalemissionfromanac- presentedradio–to–X-raySEDsfor47quasarsandhasprovideda
cretion disc and inverse-Compton scattering of UV disc photons useful template for determining bolometric corrections and iden-
byacoronaabovethedisc.AdustytoruspartiallyabsorbstheUV tifying trends in the SED shapes across a range of AGN prop-
photons from the accretion disc, re-emitting them more isotropi- erties. Recent studies have confirmed the usefulness of the av-
callyintheinfrared.Inthisstudy,weaimtorecoverthetrueaccre- erage bolometric corrections and SED parameters from E94, but
tionluminosityinarepresentativesampleofAGN,andusethese the sample of quasars used was predominantly X-ray bright and
(cid:13)c 0000RAS
2 R.V. Vasudevan,R. F.Mushotzky,L. M. Winter& A.C. Fabian
their bolometric luminosities included the re-processed infrared
Filter Centralwavelength(A˚)
emission. Richardsetal. (2006) present infrared–to–X-ray SEDs
for 259 quasars selected by a combination of optical and mid- V 5468
infraredcolourselectioncriteria,andhighlightthespreadinSED B 4392
parameters withinthe sample. Thislarge spread in SED parame- U 3465
UVW1 2600
terswasknownfromE94,promptingrefinementssuchasthetem-
UVM2 2246
plateSEDofMarconietal.(2004)whoemploytheobservedcor-
UVW2 1928
relationbetweenX-ray–to–optical spectralindexandX-raylumi-
nositytoconstructaluminosity-dependent SED,andimportantly,
Table1.CentralfrequenciesoftheUVOTfilters.
they exclude the reprocessed infrared emission to avoid double-
counting of part of the accretion energy budget. A similar tem-
plate is presented by Hopkinsetal. (2007) in their study on the shapes. Most importantly, they present values of absorbing col-
bolometric quasar luminosity function. These SED templates al-
umn density N for each source, determined from fits to the X-
H
lowedthediversityofSEDshapestobetakenintoaccount when raydatafromtheliteratureandnewfitsbytheauthorsthemselves,
calculatingthesupermassiveblackholemassdensityfromtheX- andidentifythosesourcesinwhichsignificantspectralcomplexity
ray background and AGN luminosity functions. More recently,
ispresent. Inthiswork, wepreferentiallyselect thosewithlower
Vasudevan&Fabian (2007) (VF07 hereafter) presented optical– absorption and minimal spectral complexity, facilitating a more
to–X-ray SEDsfor a sample of AGN observed by the Far Ultra- straightforwardcalculationoftheaccretionluminosity.Weassume
violet Spectroscopic Explorer (FUSE), which yielded interesting
thatforsuchsources,theaccretionluminosityexcludestherepro-
trendsbetweenSEDshapeandEddingtonratio,confirmedlaterby cessedIRemissionandisprincipallyseenintheoptical–to–X-ray
Vasudevan&Fabian (2009) (VF09 hereafter) using simultaneous regime(asinVF07andVF09).Additionally,AGNwithmoreX-
data and reverberation mapping mass estimates to improve accu-
rayabsorptionareexpectedtodisplayhigherlevelsofoptical–UV
racyof thebolometricluminositiesandaccretion rates.However, reddening,thecalculationofwhichdependsonthepreciseformof
the sample of VF07 is by necessity UV-bright, as it is selected theextinctioncurveandisdifficulttoaccountforwhencalculating
byFUSEandthesampleofVF09isrestrictedtothosewhichare
thetotalluminosity.Theseconsiderationsmotivateourselectionof
bright enough in the optical/UV for reverberation mapping to be objectswithlowN .
H
carriedout.
VariabilityinAGNcanproducelargechangesinluminosity,
These considerations emphasise thepressing need for arep- overtimescalesfromhourstoyears.Inordertocatchanaccurate
resentativesampleofAGNfromwhichconclusionscanbedrawn snapshot ofthetotalenergybudget inanAGNatagiventime,it
aboutaccretionpropertiesofthewiderAGNpopulation.Onema- isthereforehighlydesirabletousesimultaneousdata.Thepoten-
jorfactorinfluencingtheselectionofAGNforsurveysisthenature tialinaccuraciesinSEDparametervaluesfromnon-simultaneous
oftheirabsorption.IthasbeenknownforsometimethatX-rayand SED data are discussed in detail in VF07 and VF09, with the
optical surveys detect different segments of the underlying AGN latterfollowing theapproach of Brocksoppetal. (2006) byusing
population (Mushotzky 2004), with X-ray surveys able to probe contemporaneousoptical–to–X-raydatafromXMM-Newton’sPN
tohigher absorbingcolumndensity.Thestandardphysical mech- and Optical Monitor instruments. In this work, we make use of
anisms for the generation of X-ray emission in AGN produce a Swift’s own co-aligned UV–optical telescope (UVOT) and X-ray
power-law,butoftenAGNexhibit X-rayspectradeviatingsignif- telescope (XRT) to determine simultaneous SEDs. Many of our
icantly from this, in part due to absorption. The geometry of the targetsubsamplefromtheSwift/BATcataloguehavesimultaneous
absorption inX-raysisthesubject of muchdebate, andthecom- UVOT and XRT observations available in the archives; typically
plexspectrainsomesourcescanbeaccountedforwitheither‘par- theUVOTdataspansixfiltersbetween5468A˚ and1928A˚,provid-
tialcovering’scenarios(Gierlin´ski&Done2004)orstrongreflec- ingawindowontoasubstantialfractionofthediscemission.The
tionfromtheaccretiondiscduetolightbending(Miniutti&Fabian centralfrequenciesoftheUVOTfiltersaregiveninTable1.
2004),andwarmabsorberscanalsocomplicateourviewofthein- Thelargewavelengthcoverage,fieldofviewandspatialreso-
trinsic emission (Reynoldsetal. 1997, Blustinetal. 2005). Many lutionoftheUVOTdataalsoallowacorrectionforthehostgalaxy
ofthereverberationmapped AGNinVF09showed signsof such fluxto beestimated for each AGN.Weemploy GALFITfor this
spectralcomplexity,andtheauthorsidentifiedthedifficultiesinre- purpose,aprogramforperforming2DfittingofPSFsandvarious
gainingthetrueaccretionluminosityinthesecases. analytical profile forms to galaxy images (Pengetal. 2002). For
The Burst Alert Telescope (BAT) on board the Swift satel- a detailed discussion of the requirements of GALFIT, the reader
lite proves invaluable for addressing many of these considera- isdirected to peruse the accompanying documentation1. We also
tions. Canonical levels of absorption (column densities NH < presentbasicresultsonthehostgalaxiesfromtheGALFITfitting
1024cm−2) imprint signatureson the0.1–10 keV X-rayband, so process.TheUVOTdatausedinthisstudyalsoclarifyhowthede-
theveryhardX-raysensitivityoftheinstrument(14–195keV)pro- greeofhostgalaxycontaminationvarieswithwavelength(UVOT
videsthecapabilitytoobserveAGNinabandpassrelativelyunaf- filter).
fectedbysuchabsorption.The9-monthcatalogueofBAT-detected Understanding variationsintheAGNSEDisimportant,and
AGN(hereaftertheSwift/BATcatalogue,Tuelleretal.2008)there- one of the main drivers of these variations appears to be the ac-
foreprovidesanunprecedentedlevelofcompleteness(withrespect cretion rate (parameterised as the Eddington ratio, L /L
bol Edd
to absorption) when surveying the AGN population as it is unbi- for an object with bolometric luminosity L and Eddington lu-
bol
ased to all but the most heavily obscured sources. The study of minosity LEdd = 1.38 × 1038[MBH/M⊙]ergs−1 for a black
Winteretal.(2009)presentsacomprehensive overview oftheX- holeofmassM ).TherecentPrincipalComponentAnalysisof
BH
ray spectral properties of the 153 sources in the Swift/BAT cata-
logue and allows us to select an appropriate sample from which
wecanbeconfidentofcalculatingaccurateluminositiesandSED 1 http://users.ociw.edu/peng/work/galfit/galfit.html
(cid:13)c 0000RAS,MNRAS000,000–000
Optical–to–X-rayemissioninlow-absorptionAGN 3
Kuraszkiewiczetal.(2008)onasampleofred2MASSAGNSEDs isdiscussedatgreaterlengthin§3.4onblackholemassdetermi-
identifytheEddingtonratioasthe‘eigenvector 1’fortheseAGN nation.Werequiredthecentroidsreportedforthe2MASSdatato
(being responsible for most of the variation in the SED shapes). be within 2.0 arcsec of the NED position in the initial case. For
BothVF09andVF07highlightsubstantialvariationsinthebolo- afewobjectswhichliejustoutsidethislimit,the2MASSimages
metric output (in comparison to the X-ray output) across the ob- weredownloadedandthelocationsprovidedwerecheckedagainst
served range of Eddington ratios, and numerous studies explore therefinedpositionsobtainedfromtheXRTandUVOTimages;if
thesethemesfurther(Shemmeretal.2008,Kellyetal.2008).Ed- aconfident identificationof acounterpart tothe X-ray AGN was
dington ratios require accurate estimates of the black hole mass made, the 2MASS data were used in further processing. At any
in AGN, but since the most accurate estimates from reverbera- rate, objects with 2MASS centroids greater than 5.0 arcsec away
tionmappingareonlyavailablefor35AGN,hereweemploythe fromtheirNEDpositionswererejectedaltogether.Threepotential
M −L correlationtocalculateblackholemasses.Thecom- objectsareexcludedfromoursamplebytheirabsencefromthecat-
BH bulge
binationofrobustdeterminationsofthebolometricluminosityand alogues(IGR21277+5656,IGRJ07597-3842andLEDA138501).
sensible estimates of the black hole mass provide great opportu- Lastly,wecheckforblazarsinthesample.TheSEDproper-
nitiesfor insight into theaccretion process. Inthiswork, wedis- tiesofblazarsmakethemunsuitable forperformingabolometric
cuss the analysis of the Swift data, the construction of SEDs,the luminositycalculationbasedonthe‘disk+power-law’modelem-
derivationofSEDparameters,theidentificationofcorrelationsand ployedheresincetheirUVandX-rayluminosityisdominatedby
trends,andfinallythehostgalaxyproperties. jetemission.Outofthe30objectswhichsatisfyalltheabovecri-
teria,fourobjectsareexlcudedbasedontheirNEDclassifactionas
blazars: Mrk 501, 2MASX J19595975+6508547, ESO362-G021
(PKS0521-36) and PKS 0548-322. The final selection of 26 ob-
2 SAMPLESELECTION
jectsispresentedinTable2,alongwiththeirredshiftsanddetails
We firstly apply a cut in intrinsic column density N(int), select- oftheSwiftobservationsused.
H
ing only those with log(N(int))< 22 from the list of objects in
H
the 9-month BAT catalogue as presented in Winteretal. (2009).
Thisisthesuggestedcrossoverpointbetween‘absorbed’and‘un- 3 PROCESSINGOFMULTIBANDDATA
absorbed’ classesofAGNintheirstudy,whichalsoclassifiesthe
Wedownloadtheoptical–UVandX-raydataforourselectionfrom
objects in the sample into two broad categories based on X-ray
HEASARC. When multiple observations were available, those
spectral properties: ‘simple’ (S) and ’complex’ (C). The S class
with the maximum UVOT exposure time and maximum number
haveX-rayspectrawhicharebestfitbyasimplepower lawwith
of UVOT filters were preferentially selected. Pipeline-processed
intrinsic and galactic absorption (sometimes with a soft excess),
whereastheCclassdisplaymorecomplexX-rayspectrawhichare ‘level2’FITSfilesarereadilyavailablefromHEASARC.Thedata
forthe26sources identifiedinsection2werethenprocessed ac-
better fit by models such as double-power laws or partial cover-
cordingtotheprocedureoutlinedinthefollowingsections.
ing(thesemodelsareillustrativeinthattheyhighlightthespectral
complexity;moredetailedfitsincludingreflectionmayalsobepos-
sible).WealsoeliminateanyobjectsfromtheCclass,astheywill
3.1 Optical–UVphotometry:Correctingforthehostgalaxy
presentdifficultieswhendeterminingthetrueaccretionluminosity
(asdiscussedinVF09). We employ the custom-built software tools designed specifically
Inorder tofacilitateprofilefitstooptical andUVimagesof forprocessingUVOTdatawherepossible.EachindividualUVOT
thehostgalaxies,wealsoimposearedshiftcut,requiringz <0.1 filter data file in general contains a number of exposures which
forourselection.Forz <0.1,theangularresolutionoftheUVOT weresummedusingthetoolUVOTIMSUM.TheUVOTSOURCEtool
(∼ 1.7 arcsec) allows separation of the nucleus from the galaxy was then used to extract magnitudes from simple aperture pho-
to a physical length scale of 3 kpc, thus allowing a reasonable tometry.Sourceandbackgroundregionswerecreatedforthispur-
galaxy–AGN separation while still yielding 54 potential objects pose, with the position of the source region being obtained from
forstudyfromthesample.WethenidentifythoseforwhichSwift theNASAExtragalacticDatabase(NED)inthefirstinstance,fol-
XRT and UVOT data are available from the High Energy Astro- lowedbyfineadjustmentofthesourceregionpositionifnecessary.
physics Science Archive Research Center (HEASARC2), yielding TherequiredsourceregionsizeforUVOTSOURCEis5arcsec,and
33 objects. For estimating black hole masses, we also obtain K- thebackgroundregioncanbeanysize(atthetimeofwriting):we
bandmagnitudesfromtheTwo-micronAll-SkySurvey(2MASS) usedbackgroundregionswithradiifrom5arcsecto∼30arcsecde-
catalogues.Thekeyrequirementforcalculatingblackholemasses pendingonthefrequencyofotherforegroundsourcesintheimage.
isanestimateofthebulgeluminosity.TheK-bandisleastsubject The magnitudes from UVOTSOURCE provide a useful first-order
tothe effectsof Galacticreddening and predominantly tracesthe estimate of the nuclear flux, and were saved for a later compari-
older stars in the bulge over the stellar populations of the galaxy sonwiththemorecarefullydeterminednuclearfluxesusingpoint
disc, motivating its selection over the J and H bands also avail- spreadfunction(PSF)fitting.
able in the 2MASS catalogues. The 2MASS data were gathered TheimageswerethenpreparedforusewithinGALFIT.One
withtwogroundbasedtelescopes:theWhippleObservatoryinAri- oftherequirementsfor accuratelydeterminingthenuclear fluxis
zona,USAandtheCerroTololotelescopeatLaSerena,Chile.The tohavesuitablePSFsavailableforeachimage.Preliminarystud-
limitationsintroducedbyground-basedobservations(mostimpor- ies of the UVOT PSF in the six filters show that the PSF shape
tantly, the level of seeing for each observation) need to be taken may depend on a variety of factors including position on the de-
intoaccountwhenattemptingtorecoverthebulgeluminosity.This tector, countrate of the source and the filter being used. Average
PSFfull-width half-maxima range between 1.7–2.5 arcsec, when
considering all six filters. As discussed by Kimetal. (2008a) in
2 http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/swift.pl thecontext ofHubbleSpaceTelescope(HST)images, thechoice
(cid:13)c 0000RAS,MNRAS000,000–000
4 R.V. Vasudevan,R. F.Mushotzky,L. M. Winter& A.C. Fabian
AGN redshift SwiftobservationID TotalUVOTexposuretime(ks) XRTexposuretime(ks)
UGC06728 0.006518 00035266001 2.1 6.33
MCG-06-30-15 0.007749 00035068003 3.19 8.72
NGC4593 0.009 00037587001 1.83 4.88
Mrk766 0.012929 00030846039 1.34 3.71
ESO548-G081 0.01448 00035250002 2.8 6.33
Mrk352 0.014864 00035243002 6.38 15.91
NGC7469 0.016317 00031245005 1.38 4.27
NGC5548 0.017175 00030022062 1.84 5.13
WKK1263 0.02443 00035268002 1.45 8.94
ESO490-G026 0.02485 00035256001 2.87 8.51
Mrk590 0.026385 00037590001 1.43 4.46
1RXSJ045205.00+493248 0.029 00035281002 0.65 1.99
SBS1301+540 0.0299 00035269001 2.3 7.85
Mrk279 0.030451 00037591001 1.75 5.22
MCG+04-22-042 0.032349 00035263001 3.0 9.11
Ark120 0.032713 00037593003 1.44 4.11
IRAS05589+2828 0.033 00035255001 2.68 5.91
3C120 0.03301 00036369001 2.1 6.37
Mrk509 0.034397 00035469003 2.5 6.8
Mrk841 0.036422 00035468002 3.33 8.4
Mrk1018 0.042436 00035166001 1.41 4.53
NGC985 0.043143 00036530005 3.16 8.65
3C390.3 0.0561 00037596001 2.25 6.46
IRAS09149-6206 0.0573 00035233002 1.87 5.04
SBS1136+594 0.0601 00035265001 3.22 9.17
2MASXJ21140128+8204483 0.084 00035624002 1.72 5.09
Table2.DetailsofUVOTobservationsusedfortheobjectsinoursample.
of PSF can significantly affect PSF fitting results, since a poorly PSFswereusedinGALFITtomodelthecentralAGNinthegalaxy
chosen PSFcan give profile parameters that deviate dramatically profiles.
from their ‘true’ values (also see Simmons&Urry 2008 for an- When this approach was not possible due to lack of guide
otherdiscussionofthefactorsaffectingAGN–host-galaxydecom- stardetectionswithinreasonablecount-ratelimits(orlackofpoint
position).TomitigatetheseproblemsandminimizePSFmismatch, sourceswhichwerealsoidentifiedintheguidestarcatalogue),the
weadopted thefollowingapproaches. Thefirstand preferred ap- filterimagewasviewedusingthe XIMAGEpackage anda‘King’
proachwastogenerateauniquePSFforeachfilterimagefroma profilemodelwasfittoanidentifiablepointsourcewhichlooked
fewknownguidestarsintheimage,requiringthestarsselectedto similarinformandintensitytotheAGNnucleus.Theparameters
be withinacertainrange of thecount rateof the source of inter- fromthefitwerethenusedasamodelforthePSFinGALFIT(via
est (as determined from simple aperture photometry with UVOT- the‘Moffat’modeloption),inlieuofarealPSFimage.Inthevast
SOURCE).Firstly,theUVOTutilityUVOTDETECTwasusedtopro- majorityofcases,arealPSFimagecouldbeextractedfromtheim-
videalistofdetectablesourcesineachimage(UVOTSOURCEes- agesanda‘King/Moffat’modelPSFwasrarelyrequired.Inonly
sentiallyusestheSEXTRACTORpackage forthispurpose).These onefilterimageforoneobject,aGaussianmodelwasfoundtofit
were then cross-checked against published catalogues of known thenucleus betterthan other availablemodels, withtheGaussian
guidestarpositions.The XBROWSEtoolinthe HEASOFTsuiteof widthfixedattheaverageFWHMoftheUVOTPSFinthatfilter
utilitiesprovidesaccess tomany suchcatalogues, such astheUS asreportedintheCALDBdocumentation4.
NavalObservatory(USNO)andHST guidestarcatalogues.Typi- ThePSForPSFmodelthusgeneratedwasthenfitalongwith
cally,theUSNOcataloguewasusedtoobtainalistofsuchstars, other galaxy profile components in GALFIT.We performed tests
requiring them to be within 13 arcmin of the AGN of interest to to ascertain the level of detail discernible within the UVOT im-
ensuretheywerewithintheUVOTfieldof view.Theguide stars ages,startinginitiallywithafour-component modelconsistingof
wereselectedsuchthatbetween3-20 starswereusedtogenerate a constant sky background, acentral nuclear point source, a Ser-
eachPSFimage.ForthelowestenergyV-band,thistranslatedinto sicprofileforthegalaxybulgeandanouterexponentialdisk.Such
a requirement that the stars were typically within 0.1–0.2 dex of testsoverwhelminglyindicatedthatfourcomponentsincorporated
thetargetAGNcountrate;forthehighestenergyUVW2band,the toohighadegreeofdegeneracy,duetothelargeUVOTPSFsize.
limitswere typically within1.5-2.0 dex of the target AGN count ThePSFoftheUVOTinstrumentistypicallythesamesizeasthe
ratetoobtainasimilarnumberofguidestars.Finally,theregions galaxybulgewouldbeinhigherresolutionimagesofgalaxiesnear
of the images containing these stars were then summed to form redshift ∼0.05, and indeed for some of the more distant sources,
a final PSF image, using IDL code by A. A. Breeveld3 designed theUVOTPSFisaslargeasthehostgalaxyitself.OftentheSer-
specificallyforgeneratingPSFsfromUVOTimages.Theresulting sicprofilecomponentwouldshrinktoasizecomparabletothatof
3 MullardSpaceScienceLaboratory-http://www.mssl.ucl.ac.uk/ 4 http://heasarc.nasa.gov/docs/heasarc/caldb/swift/docs/uvot/
(cid:13)c 0000RAS,MNRAS000,000–000
Optical–to–X-rayemissioninlow-absorptionAGN 5
thePSF,andwould‘absorb’someofthefluxwhichwouldother- itshouldthereforebemorereadilyidentifiableintheHSTimages.
wisebeenreportedascomingfromthePSFcomponent.Therefore, WeperformsimpleaperturephotometryusingtheDS9packageon
threecomponentswereadoptedassufficienttogivesensiblemodel imagesfromACSfortheF550MandF330Wfilters(centeredon
reconstructionsoftheprofilesseenintheimages(sky+PSF+ex- 5580A˚ and 3353A˚ respectively). We extract counts from the nu-
ponential disk).Toget asaccuratearepresentation aspossibleof cleus with a circular region withradius 0.2 arcsec, which should
the nuclear flux, the following iterative algorthim was employed provideanupperlimitonthenuclearfluxandcontain>90percent
usingGALFIT: ofthecountsfromthenucleus.Wealsodeterminethetotalcounts
froma5arcsecregion,asusedwithUVOTSOURCEforcomparison.
(i) Allbrightforegroundstarswereexcludedfromthefitbycre-
In the F550M filter (closest to the UVOT V-band in wave-
atingabadpixelmaskwhichcoveredtheseunwantedobjects.
length),weidentifyadifferenceinfluxesofafactor∼5between
(ii) Theskybackgroundwasfitindependentlytoablankregion
thesmallerandlargeraperturesforHST.Incomparison,thediffer-
oftheskyclosetotheAGNofinterest.
enceinfluxesbetweenthe5.0arcsecUVOTSOURCEmagnitudeand
(iii) The central point source and sky were fit together, keep-
thatfromPSFfittingtotheUVOTimageisafactor∼2.4.Assum-
ingtheskyparametersconstantfromthepreviousstep.Thecentral
ingthe5.0arcsecfluxesfromthetwoinstrumentsshouldtheoreti-
pointsourcemagnitudewasseededwiththatobtainedfromUVOT-
callybeidentical,thisimpliesthatthefluxreportedtothenucleus
SOURCEaperturephotometry,toprovideasensibleinitialguessof
byPSFfittingtoUVOTimagesisafactor∼5.0/2.4toolarge.The
thenuclearflux.
problemislessacuteintheF330Wfilter(closesttotheUVOTU-
(iv) The sky, central source and exponential disk components
band),withanidenticalanalysisyieldingthatthenuclearfluxfrom
werefittedtogether,keepingtheskyandcentralsourceparameters
theUVOTimageisafactor∼ 1.8/1.2 ofthatfromtheHSTim-
fixedatthevaluesfromthepreviousstep.
age.ThereisalsotheissueofopticalAGNvariability,whichcould
Afterthesesteps,theresultantmodelfitswerecomparedwith be artificially increasing these ratios (the continuum near 5100A˚
theoriginalimagesandtheresidualimagesobtainedfromsubtract- isknowntovarybyfactorsof∼ 7inthecaseofNGC5548;see
ing themodel from the datawere inspected. In thefirst instance, Petersonetal.1999),butitisdifficulttodisentanglethisfromthe
thepositionsofthedifferentcomponentswereleftfreetofit.Ifany errorintrinsictotheinstrument,andthefactorswecalculatehere
obvioussignsofPSFmismatchorotherproblemswiththefitwere are therefore probably upper limits. This reflects a fundamental
evident, these positions were frozen manually by inspection and limitation of the resolution of the UVOT images, but the subse-
thefitwasre-evaluated.Insomecases,suchasforpoint-likeAGN quentanalysisshowsthatinmanyoftheobjectsseen,attempting
atthehigherendofourredshiftrange,asimplermodelconsisting toremovethehostgalaxydoesproduceanoptical–UVSEDshape
ofjustaPSFandaconstantbackground wasadopted,ifthefirst- closertothatexpectedforanAGNdespitepossibleoverestimates
passattemptatfittinganexponentialdiskdidnotshowasignificant of the nuclear flux. A more detailed analysis using observations
galaxy diskcomponent. WherethePSFimage displayed obvious fromtheKittPeakNationalObservatory(KPNO)2.1mtelescope
PSFmismatch,a‘King’profilefitwasalsoattempted.Thebestfit shouldprovideamuchmoredetailedgalaxyprofiledecomposition
obtained from all these approaches, determined by visual inspec- (Kossetal.inprep),whichwillmakeuseofthesmallerPSFavail-
tionof theresidual image, waschosen toobtain thefinal nuclear ablewiththeKPNO(FWHM∼1.0–1.4arcsec).
magnitudes.Anexampleofthesky-nucleus-diskdecompositionis
showninFig.2.Thechoicesofprofilesusedforeachfilterineach
3.2 Optical–UVphotometry:Correctingforcoincidenceloss
objectaregivenintable3.
andGalacticextinction
For AGN with very high count rates, the fluxes obtained from
3.1.1 ComparisonwithHST
UVOT images are highly susceptible to coincidence losses and
ThedetailedstudyofBentzetal.(2006)highlightstheneedtotake therefore often appear lower than their true values. Coincidence
into account host galaxy contamination when calculating nuclear lossreferstothephenomenonwheremultiplephotonsarriveatthe
luminositiesfromoptical HSTimages, specifically inthecontext same location on the detector during a single frame, and is dis-
ofdeterminingtheradius–luminosityrelationshipforthebroadline cussedindetailinPooleetal.(2008).Theythetheoreticalcorrec-
region(BLR)inAGN.Theyfindthatevenforanapertureof1arc- tiontobeappliedtothemeasuredcountrateforindividualpixels,
sec,therecanbesignificanthostgalaxycontamination. However, but also point out the need to account for the spread of a point
theHSTAdvancedCameraforSurveys(ACS)offersasignificant source over many pixels. They also provide an empirical correc-
advantage withaPSFof FWHM0.0575 arcsecincontrast tothe tion which takes the latter effect into account. We correct all of
typicalFWHMof∼2arcsecfortheUVOTPSFs.Thissomewhat ourmagnitudesfromGALFITforcoincidencelossmanuallyusing
limitsourabilitytodeterminethehostgalaxycontamination,since theseexpressions; the UVOTSOURCEaperturephotometry magni-
thestarsusedtomodelthePSFoftenareaswideinextentonthe tudesareautomaticallycorrectedforcoincidenceloss.
sky as some of the more distant galaxy disks in our sample. We There is some scope for error in the coincidence loss cor-
attempttogaugethepossibleunderestimateofhostgalaxycontri- rection when the PSF image is not quite a point source, as the
butionwithUVOTusingpublicallyavailableimagesfromtheHST coincidence loss correction only holds good for point sources.
ACSandWideFieldandPlanetaryCamera2(WFPC2)foroneof Thisproblemisespeciallypronounced forverybrightsources.In
ourobjects,NGC4593.Thisobjectisknowntohaveaclearlyiden- thesesources,thecoincidence-correctedfluxesaresometimeseven
tifiablespiralgalaxystructuresurroundingthecentralAGNsopro- greaterthanthoseobtainedfromUVOTSOURCE,whichshouldthe-
videsagoodfoundationforcomparisonbetweenUVOTandHST oretically provide an upper limiting nuclear flux. In cases where
imagequality.OurUVOTanalysisalsoshowsacleardiscrepancy this phenomenon is very pronounced, we do not use the magni-
betweenthe5.0arcsecaperturephotometryresultsandthosefrom tudes from GALFIT and instead employ the 5.0 arcsec aperture
PSFfittingintheoptical(V,BandU)bands.Sincesomelevelof photometrymagnitudesinanyfurtheranalysis.
galaxy contamination is clearly identifiable using UVOT images, After calculation of magnitudes from both GALFIT and
(cid:13)c 0000RAS,MNRAS000,000–000
6 R.V. Vasudevan,R. F.Mushotzky,L. M. Winter& A.C. Fabian
100 200 300 400 500600700800 100 200 300 400 500600700800 100 200 300 400 500600700800
100 200 300 400 500600700800900 100 200 300 400 500600700800900 100 200 300 400 500600700800900
100 200 300 400500 100 200 300 400500 100 200 300 400500
50 100 150 200 50 100 150 200 50 100 150 200
10 203040 10 203040 10 203040
20 4060 20 4060 20 4060
Figure1.ExampleGALFITprofilefittingresultsforMCG-06-30-15.Thefirstcolumnineachrowshowstheoriginaldataimage,thesecondshowsthemodel
fitandthethirdshowstheresidualobtainedfromsubtractingthemodelfromthedata.Therows,fromtoptobottom,showtheresultsfortheV,B,U,UVW1,
UVM2andUVW2bands,inthatorder.IntheVandBband,theresidualsimplythatabulgecomponentmayalsobediscernibleinthisobject,buttheUVOT
datadidnotallowrobustfitsincludingabulgecomponentformanyofourobjects.AsimpleanalysisusingDS9regionsindicatethattheputativebulgemay
accountforupto10percentofthetotalgalaxyfluxintheVandBbandimages.
UVOTSOURCE,these magnitudes were corrected for Galactic ex- 3.3 X-rayspectrafromXRT
tinctionusingthevaluesforE(B−V) fromtheNASA/IPAC
Gal
Infrared Science Archive5 and the Galactic extinction curve of
Cardellietal.(1989).ThefinalmagnitudeswereturnedintoXSPEC
PHAfilesusingtheFLX2XSPutility,tofacilitatefittingalongwith Thepipeline-processedeventfilesfromtheXRTdetectorwerepro-
thecontemporaneousXRTdatausingtheXSPECanalysissoftware. cessedusingthe XSELECTpackage, asdirectedintheSwiftXRT
user guide. Source regions of 50 arcsec were used, with larger
accompanying background regions (averageradius∼150arcsec).
Backgroundlightcurvesweredeterminedfromtheeventfilesand
inspectedforflaring,butthiswasnotfoundtobeaprobleminany
ofourobservations.Sourceandbackgroundspectrawereextracted,
andthesourcespectraweregroupedwithaminimumof20counts
5 http://irsa.ipac.caltech.edu/applications/DUST/ perbin.
(cid:13)c 0000RAS,MNRAS000,000–000
Optical–to–X-rayemissioninlow-absorptionAGN 7
AGN V B U UVW1 UVM2 UVW2
1RXSJ045205.00+493248 P P P P – –
2MASXJ21140128+8204483 P+E P P+E P P+E P+E
3C120 P+E P+E P+E P+E M+E P+E
3C390.3 P+E P+E P P P+E P+E
Ark120 P+E P+E P+E P+E P+E P+E
ESO490-G026 P+E P+E P+E P+E P+E P+E
ESO548-G081* P+E P+E P+E P+E M+E M+E
IRAS05589+2828 P P P P M Gaussian
IRAS09149-6206 P+E M P+E P+E P+E P+E
MCG+04-22-042 P+E P+E P+E P+E M+E P+E
MCG-06-30-15 P+E P+E P+E P+E P+E P+E
Mrk1018 P+E P+E P+E P+E M+E M+E
Mrk279 P+E P+E P+E P+E P+E P+E
Mrk352 P+E P+E P+E P+E P+E M+E
Mrk509 P+E P+E P+E P+E P+E –
Mrk590 P+E P+E P+E P+E P+E P+E
Mrk766 P+E P+E P+E P+E P+E P+E
Mrk841 P+E P+E P+E P+E M+E P+E
NGC4593 P+E P+E P+E P+E P+E P+E
NGC5548 P+E P+E P+E P+E P+E P+E
NGC7469 P+E P+E P+E P+E P+E P+E
NGC985 P+E P+E P+E P+E P+E P+E
SBS1136+594 P P P+E P+E P+E P+E
SBS1301+540 P+E P P+E P P P+E
UGC06728 P+E P+E P+E P+E – P+E
WKK1263 P+E P+E P P P P
Table3.TableshowingthemodelcomponentsusedinGALFITwitheachfilterimageforeachAGN.‘P’signifiesaPSFgeneratedfromguidestarswithin
appropriatecount-rateranges,fromeachimage,‘M’signifiesaMoffat(King)profilewithparametersestimatedfromasinglepointsourceintheimage,and
‘E’signifiesanexponentialdiskmodelcomponent..*ForESO548-G081,anextremelybrightforegroundstarwaslocatedwithin∼30arcsecoftheAGN,
renderingthephotometryobtainedsusceptibletolargeerrors.
1000 2000 3000
Figure2.ComparisonbetweenimagesfromHST(left)andUVOT(right)forthesourceNGC4593.A5arcseccircularregionisshownforreferenceonboth
images.
3.4 Blackholemassestimatesusingthe2MASSAll-Sky holemassfortheSwift-BATcatalogueAGNfrom2MASSK-band
SurveyCatalogues totalsourcemagnitudes,whichinvolvessubtractingthecentralnu-
clear component from the extended source flux to estimate the
bulgeluminosity.Weattempttorefinethismethodherebyincorpo-
TheM −L correlationforgalaxiesprovidesausefulway
BH bulge ratinginformationontheexpectedangularsizeofthebulgeonthe
ofestimatingtheircentralblackholemasses.Thekeychallengeis
skyandtheresolutionlimitationsofthe2MASSdata.Thecrucial
toobtainanaccurateestimateofthebulgeluminosity.Thestudyof
factor is the degree of seeing affecting the 2MASS observations;
Marconi&Hunt(2003)presentsadecompositionofimagesfrom
typically the seeing takes a value of 2.6 arcsec. For bulges with
2MASSusingGALFITtoobtainthebulgeluminosityandcorre-
typical size ∼ 0.5−1 kpc (Graham&Worley 2008), the bulge
late it with the black hole mass from direct determination meth-
becomes unresolvable at redshifts of about z ≈ 0.01 (assuming
ods (stellar or gas kinematics, maser kinematics, etc.). However,
H =71kms−1Mpc−1,Ω =0.27andaflatUniverse).There-
the redshifts of the objects under scrutiny here are generally sig- 0 M
fore,fortheoverwhelmingmajorityofobjectsinour sample,the
nificantlyhigherthanthoseinMarconi&Hunt(2003),presenting
bulge should be unresolved. Inspection of the atlas images from
problemsforperformingafullnucleus-bulge-discdecomposition.
2MASSforthelowestredshiftobjectsinoursampleconfirmsthat
Mushotzkyetal.(2008)presentamethodforcalculationofblack
(cid:13)c 0000RAS,MNRAS000,000–000
8 R.V. Vasudevan,R. F.Mushotzky,L. M. Winter& A.C. Fabian
thevisuallyidentifiablebulgecomponentisnotresolved.Thebulge 42.0 < log(L ) < 43.0, 43.0 < log(L ) < 44.0, 44.0 <
X X
light istherefore mixedinwiththe nuclear light inthesesources log(L ) < 45.0). The fractions are plotted in Fig. 3 against the
X
andidentifiedasa‘point source’.Thepoint sourcesidentifiedby central luminosity of each bin. We also plot a logarithmic inter-
2MASS have been collated, along with their magnitudes, in the polation between the points, to allow determination of the ratio
2MASSPointSourceCatalogue(PSC);similarlyextendedsources of LK,host/LK,total at ageneral value of LX, assuming theratio
have been catalogued in the 2MASS Extended Source Catalogue variescontinuously. Forvalues of L greater thanthose spanned
X
(XSC).Basedonour assumptionthat thebulgeisunresolved, we bytheSilvaetal.(2004)study,wesimplyemploythefractioncal-
initially download only the magnitudes from the PSC for further culated for L = 1045ergs−1, extrapolating from the direction
X
use,astheywillcontainthebulkofthebulgelightwewishtore- ofthetrendshownbetweenthebinscentred onlog(L ) = 43.5
X
cover. and 44.5. For luminosities log(L ) < 41.5, we use the fraction
X
Bywayofcalibratingourattempttoobtainblackholemasses, evaluatedatlog(LX) = 41.5(extrapolatingfromthetrendwould
we first turn to the reverberation mapping (RM) sample of AGN yieldfractionslargerthanUnity).Thehighluminosityextrapola-
presented by Petersonetal. (2004), representing the most secure tionisclearlynotlikelytobeaccurateforextremelypowerfulob-
massdeterminationsforAGNtodate(augmentedwiththerefined jects(logLX > 46), butnone ofthereverberation mappedAGN
result from Denneyetal. 2006 for NGC 4593). There are uncer- ortheAGNinourSwift-BATsubsampleareinthisregime.Inthe
taintiesintheRMmethod,connectedtoassumptionsaboutthege- absenceofinformationonIRSEDsoutsidethisluminosityrange
ometry of the broad-line region and whether it is gravitationally wedonotattemptamorecomplexextrapolation.
bound,butthe∼35AGNforwhichRMmassestimatesexistnev- Before using these fractions to calculate bulge luminosities
erthelessconstitutethesampleofAGNwiththemostcarefullyde- fromthe2MASSPSCmagnitudes, weconsider potentialsources
terminedblackholemasses.Initially,wedownloadthe2MASSat- of bias. SinceSilvaetal.(2004) adopt areprocessing scenario to
lasimagesforthoseRMAGNbelow aredshiftof0.01,inwhich accountfortheK-bandcontinuum,itispossiblethatthemodelnu-
thebulgeshouldbetheoreticallyresolvedandperformaGALFIT clearK-bandluminosityisafunctionoftheEddingtonratio(since
3-component decompositionusingagaussianPSFforthenuclear itisultimatelylinkedtotheUVaccretiondiscluminosity,thedom-
pointsource,aSersicbulgeandanexponentialdisc.OurGALFIT inantcomponent ofthetotalaccretionluminosity).TheX-raylu-
analysis yields that there is a significant degree of uncertainty in minositycanberecastastheproductoftheEddingtonratio,bolo-
the identification of the bulge component in these AGN, and the metric correction and black hole mass (via the Eddington ratio),
magnitudeascribedtothebulgeisheavilydependent ontheprior so the trend seen in Fig. 3 could be the result of two functions
constraintsimposed.Weexploreanumberofdifferentconstraints ofEddington ratiobeingplottedagainst eachother. However, we
onthemodelprofiles;forexample,theSersicindexnisoftencon- again note the low X-ray luminosities probed by the Swift/BAT
strained toan upper limitto avoidthefittingroutine confusing it 9-monthcatalogue(uptoafewtimes1044ergs−1),andfindthat
withthe nuclear point source, and often requires alower limitto the host-to-total fraction varies at most by a factor of two inthis
avoidconfusionwiththedisccomponent.Despitesuchstrategies, regime.Therefore,thedependenceisnotstrongandwillnotintro-
insomesourcesthebulgeanddiscprofilesacquireverysimilaror ducesignificantbiasescomparedtoothersourcesoferror,suchas
identicalradiiand‘share’thediscluminosity,withtheSersicpro- the intrinsic spread in RM masses and the intrinsic dispersion of
filepartiallytracingthediscinsteadofthebulge.Insuchsources, theMBH −LK,bulge relation.Regardlessoftheparticularmodel
three-componentmodelfitsdonotyeildmeaningfulbulgeparame- used topredict thenuclear K-band continuum, itisclear that the
ters.OurattemptsatconstrainingthebulgeusingGALFITresultin fraction of an unresolved bulge that isattributable to the nucleus
bulgeluminositiesthatvarybyuptoanorderofmagnitudedepend- willdecreaseforlowerluminosityAGNandviceversa;thesimple
ingonthechoiceofmodelandconstraintsimposed,andshowthat relationship inFig.3 provides an observationally-rooted estimate
evenfortheclosebysources,thebulgesareprobablynotresolved. ofthiseffect.
In light of this, we then employ the 2MASS PSC catalogue WeemploythevaluesofLXfromXMM-Newtonreportedin
magnitudestoprovideasimpleestimateofthetotalbulgeandnu- Vasudevan&Fabian (2009) to calculate the K-band host-to-total
clearflux.Inordertoestimatetherelativecontributionsofthenu- ratioforeachoftheRMobjects,andassumetheSilvaetal.(2004)
cleus and bulge in the PSC magnitudes, we employ the infrared Seyfert1IRSEDtemplateforallobjectsinthesample.Intheab-
SEDtemplatespresentedinSilvaetal.(2004).Intheirstudy,they senceofadetailed,uniformstudyontheabsorbingcolumnsofthe
presentnuclearIRSEDtemplatesconstructedusingavailablenear- RMAGNsamplethisisareasonableassumption,sincetherever-
to-midIRdataon33Seyferts,usingaradiativetransfermodelsfor berationmappingsampleisheavilybiasedtowardsSeyfert1AGN;
dustheatingtointerpolatebetweenthewavelengthscoveredbythe noneoftheRMAGNareclassifiedasSeyfert2sinNED.Wescale
data.TheyalsopresenthostgalaxySEDtemplatesbysubtracting thePSCmagnitude bythe appropriate fraction, usingtheexpres-
thenucleartemplatecontributionfromthetotalphotometryateach sion
availablewavelength. Theypresent anumber of different nuclear
SEDtemplatesappropriatefordifferentlevelsofX-rayabsorption,
andhost SEDtemplatesarepresented fordifferent intrinsic2–10 MK,bulge =MK,PSC−2.5log10(fbulge(LX)), (1)
keVAGNluminosity(LX)regimes.Usingtheappropriatenuclear where the fraction fbulge = LK,host/LK,total is calculated as
SED along with the corresponding host galaxy SED, it is there- above.TheblackholemassesarethencalculatedusingtheM −
BH
forepossibletoestimatethefractionofthetotalluminositywhich LK,bulge relation of Marconi&Hunt (2003). The resulting mass
canbeaccountedforbythehostforanAGNwithaparticularL . estimatesarecomparedwithRMmassestimatesinFig.4.
X
Intheprocesswemaketheassumptionthat,inthecaseoftheK- Areasonableagreementbetweenthetwomethodsisseen,al-
band,thehostfluxshouldbedominatedbythebulgeasdiscussed beit with some significant deviation at higher masses. The grey
in §1. We calculate the ratio of host to total luminosity (nuclear shaded areahighlightstheuncertaintiesinRMmassesduetothe
plushostluminosity)fromtheseSEDtemplatesintheK-bandfor lackof preciseknowledge of theBLRgeometry. Thelargestdis-
the four different luminosity regimes (41.0 < log(L ) < 42.0, crepancyisfortheAGNwiththehighestmass,3C273,forwhich
X
(cid:13)c 0000RAS,MNRAS000,000–000
Optical–to–X-rayemissioninlow-absorptionAGN 9
11
1
0.9 des10
u
nit
0.8 mag
LK,total 0.7 ASS PSC 9
=L/K,host 00..56 m scaling 2M 8
fbulge 00..34 (bulge) froMK
om 7
0.2 M frBH
0.1
6
40 41 42 43 44 45 46
6 7 8 9 10 11
log(LX) Reverberation mapping MBH
Figure3.Variation ofLK,host/LK,total withX-rayluminosity, extrap- Figure 4. Comparison between masses from reverberation mapping and
olated fromthehostandnuclear IRSEDtemplates ofSilvaetal.(2004) massesestimatedfromK-bandbulgeluminosities.Thesolidlinerepresents
(black filledpoints -determined usingthefourfiducialluminosities pro- thedesired one-to-one correspondence between thetwomethods andthe
videdintheirpaper;solidline-extrapolation between points asdetailed shadedareadepictstheintrinsicuncertaintiesinreverberationmapping.The
inthetext).Thesefractions areemployedtocalculate thecontributionof dashed line shows thebest fitoftheform log(MBH,LK,bulge) = A+
thebulge tothe2MASS point sourcemagnitudes, fordetermining black log(MBH,revamp).
holemasses.ThecurveforanAGNwithintrinsicX-rayabsorptionNH =
1023.5cm−2 isshown(dashedline)forcomparison(thecurvesforother
absorptionsaboveNH = 1022cm−2areverysimilar;thesignificantdif- gestapossiblecontributortothisoffsetandpresentacorrectionfor
ferenceisbetweenobscuredandunobscuredAGN). it.
The Silvaetal. (2004) host galaxy SEDs have been calcu-
lated using large-aperture and extended-source data (such as the
theK-bandbulgeluminosity estimategives ablack holemassan 2MASS XSC catalogue magnitudes) which could include more
order of magnitude too high. This is known to be a very power- thanthebulgelight.Ifthegalaxydiscissignificantinsomecases,
fulobject,anditispossiblethatoursimpleapproachtoestimating theSilvaetal.(2004)host-to-totalratiosactuallyprovidethefrac-
thebulgefractioninthepointsourcelighthasstillunderestimated tion of bulge plus galaxy disc to the total luminosity rather than
thepowerful nucleus. Thereisalsolikelytobeasignificant syn- justthebulge,andthereforeusingthemtoscalethe‘nucleusplus
chrotron (non-accretion) contribution to fluxes at all wavelengths bulge’luminositiesfromthe2MASSPSCisnotstrictlycorrect.It
inthissource,whichfurtherincreasesuncertainties.ThisAGNis isthereforenecessarytogaugetheeffectofneglectingthegalaxy
far more powerful than the majority of the Swift-BAT catalogue disc in thiscalculation. We do this by obtaining the 2MASS Ex-
AGN, so such problems are not likely to affect the lower-power tended SourceCatalogue magnitudes (matching thecentroids ap-
objectsweconsiderhere. propriatelyas before), using thesefluxesasestimatesof thetotal
Marconietal.(2008)pointoutthatthepreviousreverberation nuclear, bulge and disc light (L = L +L +L ).
total nuc bulge disc
massestimateshavebeencalculatedwiththeassumptionthatthe Employing thePSCmagnitudes asthebulgeand nuclear light as
BLRisgravitationallybound,andintroduceacorrectionbasedon before(L +L ),wethencanutilisethefractionofnuclear-
bulge nuc
anestimator of theaccretion rate(the5100A˚ monochromatic lu- to-total luminosity predicted from the Silvaetal. (2004) IR SED
minosity)toproviderevisedmassestimatesfortheRMAGNcat- templates(f =L /[L +L +L ])toobtainathe-
nuc nuc nuc bulge disc
alogue.Wealsoprovideacomparisonwiththeirrevisedmasses- oreticallymoreaccurateestimateofthebulgemagnitude:
timates, in Fig. 5. The correlation between the two mass estima-
torsisstrengthenedsignificantlyifthesefirst-ordercorrectionsto
thereverberation massesareapplied,andparticularlyreducesthe MK(2,)bulge=MK,PSC−2.5log10(1−fnuc10MK,PSC2−.5MK,XSC)),
scatterseenforthoseobjectswithhighaccretionrates(forwhich (2)
thecorrectionismaximalandworkstoincreasethereverberation Thisexpression isobtained by solving for L fromtheavail-
bulge
massestimate).Theoffsetisstillpresenthowever,andasimplefit able quantities. Put simply, it arises from using the nuclear frac-
of the form log(MBH,LK,bulge) = A+log(MBH,revamp) yields tionfromtheIRSEDtemplatestoestimatethenuclearfluxfrom
A ≈ 0.57inbothcases(usingreverberationmasseswithorwith- the XSC flux; this nuclear component is then subtracted from
outcorrectionforradiationpressure),implyinganoffsetofafactor the PSC flux to obtain the bulge flux. This estimate is not avail-
ofupto∼ 3.7inblackholemass,justoutsidethetypicalquoted able for all of the objects available previously, as some objects
toleranceforreverberationmasses(afactorof∼ 3).Wenowsug- do not have 2MASS XSC magnitudes. For a couple of sources,
(cid:13)c 0000RAS,MNRAS000,000–000
10 R.V. Vasudevan,R. F.Mushotzky,L. M.Winter&A. C. Fabian
11 11
S10 10
AS
003) from 2M 9 & Hunt 2003) 9
& Hunt 2 Marconi
M from L (Marconi BHK,bulge 78 log(M) from L (BHK,bulge 78
6 6
6 7 8 9 10 11 6 7 8 9 10 11
MBH from reverberation mapping (corrected for radiation pressure effects) log(MBH) from reverberation mapping
Figure5.ComparisonbetweenmassesfromRM(corrected forradiation Figure 6. Comparison between masses from reverberation mapping and
pressureeffectsasdiscussedbyMarconietal.2008)andmassesestimated massesestimatedfromK-bandbulgeluminosities (withoffsetduetoun-
fromK-bandbulgeluminosities.Theemptywhitecirclesshowtheresults derestimationofthegalaxydisccontributiontakenintoaccount).Keyasin
using the reverberation masses before correcting for radiation pressure. Fig.5.
OtherkeyconventionsasinFig.4
(2009),andtheN valuesinthesamepaperareusedtoselectbe-
H
the predicted fraction fnuc = Lnuc/(Lnuc + Lbulge + Ldisc) tweenthetwohost-to-totalratiocurvesforobscuredorunobscured
fromtheSilvaetal.(2004)templateswaslargerthanthefraction AGN(Fig. 3) asrequired. Bywayof another check ontheaccu-
(Lnuc+Lbulge)/(Lnuc+Lbulge+Ldisc)foundfromtheratioofthe racyofourmassestimates,therecentstudyofWangetal.(2009)
PSCandXSCfluxes,leadingtoanimpossiblesolutionforLbulge. presentsvirialmassestimatesforasampleofSeyfertswhichpar-
Thisindicates that the nuclear-to-total fraction obtained from the tiallyoverlapswithSwift-BAT9-monthcatalogueAGN,usingthe
Silvaetal. (2004) templates is not appropriate for that object, or single-epoch Hβ linewidth-based black hole mass estimator (as
thatthebulgeisnotcompletelycontainedinthePSCflux.These giveninGreene&Ho2005).Weplotacomparisonbetweentheir
problemslimittheuseofthismethod,butforthoseobjectswherea valuesandoursinFig.7forthe24overlappingobjects.Whilethe
calculationispossible,wefindthatthenewK-bandmassestimates relation shows some scatter, we caution that the linewidth-based
are systematically shifted down by 0.14 dex (afactor 0.72) from black hole mass estimation methods also show significant scatter
thevaluesfromthesimplerapproachofusingthePSCmagnitude themselveswhencomparedtoRM.Thetwoestimatorsstillappear
alone. We therefore apply this correction to all masses obtained to trace each other (with a correlation coefficient of 0.80); addi-
using the PSC alone, which brings the best-fit line for the new tionally, preliminary calculations of black hole masses from Kitt
mass estimates within the tolerance of the reverberation masses. PeakNationalObservatory(KPNO)andSloanDigitalSkySurvey
The strength of the correlation is good, asindicated by the Pear- (SDSS) spectra for the Swift/BAT 9-month catalogue AGN also
soncorrelationcoefficientsof0.83and0.93obtained(correlating seemtomatchourestimateswell,withascatterofafactorof∼2
withreverberationmassesbeforeandafterradiationpressurecor- (Winter et al., Koss et al. in prep). We see some indications that
rection).Thisanalysisalsoindicatesthatthegalaxydisccontribu- thelocalSwift-BAT9-monthcatalogueAGNhavepredominantly
tioninthehost-to-totalratiosisoftheorder∼ 30percent,anda lowblackholemasses,asexpectedin‘anti-hierarchical’structure
similarvalueappliestoallAGNintheRMsample.Therestillre- formation scenarios. The masses thus determined are used in all
mainssomeoffsetabovereverberationandwithinthetolerancere- subsequentanalysesforcalculationofaccretionratesandforcon-
gion,butanyfurtherattempttoaccountforthisissomewhatredun- strainingaccretiondiscmodelsinSEDconstruction.
dantinlightoftheintrinsicuncertaintiesinreverberationmasses,
sowedonotmakeanyothercorrectionstoourapproach.Theoff-
setofvirialmassestimatesbelowtheM −L relationhas
BH bulge 4 GENERATIONOFSPECTRALENERGY
beennotedanddiscussedindetailbyKimetal.(2008b);theyfind
DISTRIBUTIONS
that it isacomplex function of avariety of parameters including
theblackholeaccretionrateandhostgalaxymorphology. We fit the optical, UV and X-ray SED data points with a simple
Wefinallycalculatethemassesusingthisapproachforallof multicolour disc DISKPN and absorbed power-law model combi-
thez<0.1objectsintheSwift-BAT9-monthcatalogueforwhich nationusingXSPEC,followingtheapproachoutlinedinVF09.In
2MASS PSC magnitudes are available. The K-band host-to-total thiswork,weextendtheapproachofVF09byinclusionofamulti-
ratiosarecalculatedusingtheLX valuesreportedinWinteretal. plicativeZDUSTcomponentontheDISKPNmodelusedfortheUV
(cid:13)c 0000RAS,MNRAS000,000–000