Does the obscured AGN fraction really depend on luminosity?

19 Pages·2015·1.74 MB·English

MNRAS454,1202–1220(2015) doi:10.1093/mnras/stv2069
Does the obscured AGN fraction really depend on luminosity?
S. Sazonov,1,2‹ E. Churazov1,3 and R. Krivonos1
1SpaceResearchInstitute,RussianAcademyofSciences,Profsoyuznaya84/32,117997Moscow,Russia
2MoscowInstituteofPhysicsandTechnology,InstitutskyPer.9,141700Dolgoprudny,Russia
3Max-Planck-Institutfu¨rAstrophysik,Karl-Schwarzschild-Str.1,D-85740GarchingbeiMu¨nchen,Germany
Accepted2015September2.Received2015September2;inoriginalform2015July14
ABSTRACT
D
We use a sample of 151 local non-blazar active galactic nuclei (AGN) selected from the o
w
INTEGRAL all-sky hard X-ray survey to investigate if the observed declining trend of the nlo
a
fraction of obscured (i.e. showing X-ray absorption) AGN with increasing luminosity is d
e
d
mostlyanintrinsicorselectioneffect.Usingatorus-obscurationmodel,wedemonstratethat fro
in addition to negative bias, due to absorption in the torus, in finding obscured AGN in m
h
hardX-rayflux-limitedsurveys,thereisalsopositivebiasinfindingunobscuredAGN,dueto ttp
Comptonreflectioninthetorus.Thesebiasescanbeevenstrongertakingintoaccountplausible ://m
n
intrinsiccollimationofhardX-rayemissionalongtheaxisoftheobscuringtorus.Giventhe ra
s
AGNluminosityfunction,whichsteepensathighluminosities,theseobservationalbiaseslead .ox
fo
to a decreasing observed fraction of obscured AGN with increasing luminosity even if this rd
jo
fractionhasnointrinsicluminositydependence.WefindthatifthecentralhardX-raysource u
rn
inAGNisisotropic,theintrinsic(i.e.correctedforbiases)obscuredAGNfractionstillshowsa als
.o
decliningtrendwithluminosity,althoughtheintrinsicobscuredfractionissignificantlylarger rg
than the observed one: the actual fraction is larger than ∼85percent at L (cid:2) 1042.5erg s−1 at C/
(a1n7g–le60θkoefVa)n,aonbdscduercinregastoersutso,(cid:2)th6is0ipmeprlcieensttahtaLt θ(cid:3)(cid:2)103404◦eirnglso−w1.erInlutemrminsosoiftythAeGhNal,f-aonpdenθin(cid:3)g aliforn
45◦ inhigherluminosityones.If,however,theemissionfromthecentralsupermassiveblack ia In
hisocleonissicsotelnlitmwaittehdaalsudmLi/ndo(cid:3)sit∝y-cinodseαp,etnhdeenintttroinrusischdaelfp-eonpdeennincegoafngthleeθob∼sc3u0re◦.dAGNfraction stitute
o
f T
Keywords: galaxies:active–galaxies:nuclei–galaxies:Seyfert. e
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h
n
o
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prompted by the fact that even hard X-ray ((cid:3)10 keV) surveys, gy
1 INTRODUCTION o
which are usually flux (or signal-to-noise ratio) limited, should n
J
AlotofrecentstudiesbasedonX-rayandhardX-rayextragalac- be biased against detection of Compton-thick AGN, i.e. objects an
u
ticsurveyshavedemonstratedthatthefractionofX-rayabsorbed viewed through absorption column density NH (cid:3) 1024cm−2, let ary
(hereafter referred to as obscured) active galactic nuclei (AGN) aloneX-raysurveysatenergiesbelow10keVwhichmustbebi- 3
1
decreases with increasing observed X-ray luminosity, at least at asedagainstevenCompton-thinobscuredsources.Duetothisde- , 2
0
(cid:3)1042ergs−1,bothinthelocal(z≈0)andhigh-redshiftUniverse tection bias, the observed fraction of obscured AGN is expected 16
(Ueda et al. 2003; Steffen et al. 2003; Hasinger 2004; Sazonov to be lower than the intrinsic fraction of such objects. Further-
& Revnivtsev 2004 ; La Franca et al.2005 ; Sazonov et al.2007; more, this effect may depend on luminosity, somehow reflecting
Hasinger2008;Beckmannetal.2009;Brightman&Nandra2011; the shape of the AGN luminosity function (LF). In fact, as dis-
Burlonetal.2011;Uedaetal.2014;Airdetal.2015;Buchneretal. cussed by Lawrence & Elvis (2010), some mid-infrared selected,
2015; note also earlier evidence, Lawrence & Elvis 1982). This radio-selected and volume-limited AGN samples do not demon-
mightindicatethattheopeningangleofthe(presumably)toroidal strateanyclearluminositydependenceoftheproportionoftype1
obscuringstructure–thekeyelementofAGNunificationschemes (i.e.containing broademissionlinesintheopticalspectrum)and
–increaseswithAGNluminosity,forexampleduetofeedbackof type2AGN.
thecentralsupermassiveblackhole(SMBH)ontheaccretionflow. Althoughtherehavebeenpreviousattempts(Uedaetal.2003;
CouldtheobservedluminositydependenceoftheobscuredAGN DellaCeccaetal.2008;Maliziaetal.2009;Burlonetal.2011;Ueda
fraction arise due to selection effects? This question has been etal.2014)totakeintoaccountdetectionbiaseswhenestimating
occasionally raised before (e.g. Mayo & Lawrence 2013 ) and is thespacedensityofobscuredAGNbasedonhardX-raysurveys,
they were, in our view, not fully self-consistent and/or used too
smallsamplesofhardX-rayselectedAGN.Itisourgoalhereto
(cid:5)E-mail:[email protected] improveonbothoftheseaspects.
(cid:6)C 2015TheAuthors
PublishedbyOxfordUniversityPressonbehalfoftheRoyalAstronomicalSociety
ObscuredAGNfractionvs.luminosity 1203
Thepurposeofthepresentstudyisto(i)evaluatetheimpacton
theobservedhardX-rayLFandobservedluminositydependenceof
theobscuredAGNfractionofthenegativebiasforobscuredAGN
discussedaboveandapositivebiasthatwedemonstratelikelyexists
forunobscuredAGN,and(ii)reconstructtheintrinsicdependence
of the fraction of obscured AGN on luminosity in the local Uni-
verse.Ourtreatmentisbasedonarealistictorus-likeobscuration
model and makes use of the INTEGRAL/IBIS 7 yr (2002–2009)
hardX-raysurveyoftheextragalacticsky.Oursampleconsistsof
∼150local(z(cid:2)0.2)Seyfertgalaxiesandishighlycompleteand
reliable.AlthoughtherearenowsignificantlylargerhardX-rayse-
lectedsamplesoflocalAGN,basedonadditionalobservationsby
INTEGRAL/IBISandespeciallybySwift/BAT,theycurrentlysuf-
ferfromsignificantincompletenessasconcernsidentificationand
absorptioncolumndensityinformation.Mostimportantly,oursam-
D
pleislargeenoughtocontainasignificantnumber,17,ofheavily o
obscured(NH≥1024cm−2)AGN,forwhichweuseasmuchaspos- wnlo
sibleN estimatesbasedonhigh-qualityhardX-rayspectraldata, a
H d
e
inparticularfromtheNuSTARobservatory,whichhasrecentlybeen d
systematicallyobservingAGNdiscoveredintheSwift/BATandIN- fro
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TEGRAL/IBIShardX-raysurveys. h
0.3WaendadHo0pt=a7(cid:6)0kcomlds−d1arMkpmca−t3t.ercosmologicalmodelwith(cid:3)m = Ffuingcutrioen1o.fCfluuxmluimlatiitvientfhraecItNioTnEoGfRtAhLe7exytrrasguarlvaecyt.ic (|b| > 5◦) sky as a ttp://mn
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2 THE INTEGRAL AGN SAMPLE xfo
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Weusethecatalogueofsources(Krivonosetal.2010b)fromthe jo
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INTEGRAL/IBIS7yrall-skyhardX-raysurvey(hereafter,theIN- rn
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TEGRAL7yrsurvey;Krivonosetal.2010a).Tominimizepossible ls.o
biasesinourstudyofthelocalAGNpopulationduetoremaining rg
a/
unidentifiedINTEGRALsourcesandobjectswithmissingdistance t C
asindde/roartioXn-rtahyeaGbasolarcpttiiconpliannfeorrmegaitoionn(,|bw|e<ex5c◦l)u.dTehferocmatatlhoeguceonis- aliforn
composedofsourcesdetectedonthetime-averaged(2002Decem- ia
ber – 2009 July) 17–60 keV map of the sky and is significance Ins
limited (5σ). The corresponding flux limit varies over the sky: titu
(fd9e0t p<er2c.e6nt×)of1t0h−e11ex(t<ra7ga×lact1i0c−(1|b1|e>rg5◦s)−s1kcym(−s2e)eFfoigr.510).percent te of T
e
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The main properties of the INTEGRAL 7 yr survey and of the h
n
corresponding catalogue of sources were described by Krivonos olo
g
etal.(2010a,b).Usingthiscatalogue,Sazonovetal.(2010)made y
o
preliminaryestimatesofthehardX-rayLFoflocalAGNandthe n
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dependence of the obscured AGN fraction on luminosity. Subse- an
u
quent follow-up efforts by different teams have resulted in addi- ary
tional identifications, classifications, distance measurements and 3
1
X-rayabsorptioncolumnestimatesformanyINTEGRALsources, , 2
0
which has significantly improved the quality of the catalogue, as Figure2. ObservedhardX-ray(17–60keV)luminosityversusredshiftfor 16
non-blazar AGN from the INTEGRAL 7 yr survey. Filled circles, empty
detailedbelow.
squaresandstarsdenoteunobscured,lightlyobscuredandheavilyobscured
The final sample used here consists of 151 non-blazar (i.e.
objects,respectively.
Seyfert-like) AGN (see Table A1 in Appendix A), with blazars
(15intotal)beingexcludedfromtheanalysis.Thesampleishighly
complete,asthereareonlyfoursourcesat|b|>5◦fromtheINTE- out that some of our objects have blazar-like properties, i.e. their
GRAL7yrcataloguethatremainunidentified.Moreover,allofour observed hard X-ray emission contains a significant contribution
AGNshaveknowndistancesandreliableestimatesoftheirabsorp- fromarelativisticjet.Themostsuspiciousinthisrespectareobjects
tioncolumnsbasedonX-rayspectroscopy.AsillustratedinFig.2, classifiedasbroad-line(i.e.presumablyorientedtowardsus)radio
oursampleismostlylocal,with146outofthe151objectsbeing galaxies.TherearesixsuchAGNsinoursample:3C111,3C120,
locatedatz<0.2,andspansaboutfivedecadesin(observed)lumi- Pic A, 3C 390.3, 4C +74.26 and S5 2116+81. All of them have
nosity,fromLobs∼1041to∼1046ergs−1(hereafter,allluminosities Lobs > 1044 erg s−1 (but <1045 erg s−1), i.e. belong to the high-
areinthe17–60keVenergyband,unlessspecifiedotherwise). luminositypartofthesample.However,thetotalnumberofobjects
Wenotethatalthoughweusedthemostup-to-dateinformation with L > 1044 erg s−1 is much larger: 42. This suggests that
obs
from the NASA/IPAC Extragalactic Database (NED) and recent possibleincompletefilteringofthesamplefromblazarsisunlikely
literaturetoremoveblazarsfromourAGNsample,wecannotrule tosignificantlyaffecttheresultsandconclusionsofthiswork.
MNRAS454,1202–1220(2015)
1204 S.Sazonov,E.ChurazovandR.Krivonos
Table1. HeavilyobscuredAGNfromtheINTEGRAL7yrsurvey.
Object D Lobs NH ReferenceforNH
(Mpc) (ergs−1) (cm−2)
SWIFTJ0025.8+6818 52.0 3.2×1042 >1025 NuSTAR(Krivonos,inpreparation)
NGC1068 12.3 3.8×1041 >1025 NuSTAR(Baueretal.2014)
NGC1194 59.0 6.6×1042 ∼1024? XMM–Newton(below10keV;Greenhill,Tilak&Madejski2008)
CGCG420-015 129.2 3.3×1043 >1025 NuSTAR(Krivonos,inpreparation)
MRK3 58.6 2.8×1043 1024 Suzaku(Ikeda,Awaki&Terashima2009)
IGRJ09253+6929 172.6 4.5×1043 >1024? LowX-ray/hardX-rayfluxratio(Swift/XRT+INTEGRAL/IBIS)
NGC3081 28.6 4.4×1042 1024 Suzaku(Eguchietal.2011)
NGC3281 46.3 1.2×1043 2×1024 BeppoSAX(Vignali&Comastri2002)
ESO506-G027 109.5 5.8×1043 1024 Suzaku(Winteretal.2009b)
NGC4939 34.7 2.3×1042 >1025? BeppoSAX(Maiolinoetal.1998),butvariedtoNH=1.5×1023cm−2
(XMM–Newton,below10keV;Guainazzietal.2005a)
NGC4945 3.4 2.6×1041 4×1024 NuSTAR(Puccettietal.2014;Brightmanetal.2015),Suzaku(Yaqoob2012) D
IGRJ14175−4641 348.3 1.6×1044 >1024? LowX-ray/hardX-rayfluxratio(Swift/XRT+INTEGRAL/IBIS) ow
NGC5643 11.8 1.7×1041 >1025 NuSTAR(Krivonos,inpreparation) nlo
NGC5728 24.8 3.2×1042 2×1024 NuSTAR(Krivonos,inpreparation) ad
IGRJ14561−3738 107.7 1.6×1043 ∼1024 Chandra+INTEGRAL/IBIS(Sazonovetal.2008) ed
ESO137-G034 33.0 1.8×1042 >1025 Suzaku(Comastrietal.2010) fro
m
NGC6240 107.3 5.8×1043 2.5×1024 NuSTAR(Krivonos,inpreparation) h
ttp
2.1 Absorptioncolumns,heavilyobscuredAGN Intotal,oursampleconsistsof67unobscured(N <1022cm−2) ://m
H n
Fcoomr pthleetepuanrpdorseelsiaobfletihnifsosrtmudatyi,onitoinstihmepXo-rrtaanytatbosohrapvtieonmcaoxliummanllsy, aonbdsc8u4redob(NscHur≥ed10(N24Hcm≥−12)02o2ncems.−2) AGNs, including 17 heavily ras.oxfo
N ,ofthestudiedAGN.Ourstartingsourceofsuchinformation Table 1 provides key information about our heavily obscured rd
iei(nsStHaaaozllu.lor2nca0ops0vree7&sv,iw2oR0uhe1sev2rnpe)iaviapttssewerwvsaes2ol0nln0eac4sthe)o,senbsauItNrthywTeaEeRnGhXdaRTpvAEoeLsu(s/p3iIbd–Bla2Iet0Se(dskseetuehVrevT)NeasybHlel(eewSsAtasiz1muo)ra.nvtoeeyvs btwAhuGeattNoatdnh.oeFepo(stIroGstuheRrvacteJen1’Ns4oH5sf6pt>h1eec−st1r3e0u,72mt53h8cei)mrseo−rafe2rflt)eheefrcretorlieimoamnbalNdeinuoNiSmnHTgiAne1saRt0tiemoodbba(stjieeensrcvtowsarthaieorivcenihdse.eictnAhacseleerl ajournals.org/
Forunobscuredandlightlyobscured(N <1024cm−2)sources, planned to be observed by NuSTAR soon or have already been t C
Xfo-rraeyvaslpueactitnrogsNcop.ySautchendeartgaiedsobeexloiswtf1o0rakHlelVofisouursusaolulyrcseusfafincdienint oobfswerrviteindgb.yHtohwisetveelre,scfoorpemboustttohfetdhaetsaeasroeuprcreosprtiheetareryexatistthsefatiimrlye aliforn
amFduoorstpthtecNramsHeos=rteh0,eiarfentHdahreceoarnbeslsiiodarebprlteisoupncuhbclosiosluhumercdneNsisHunlveoasblsuscethusa,rnewdh1.i0c2h2cwme−a2d,owpte. rNAeHGlTiaN≥hbrle1aeer0ie2no4fcfocutmrhrmre−ea2nottib–loyjnescecftearsonTimdnaibcdollauethtde1ees.rdhraiantrhdoeurXrt-hsraaaymnmpfiliresmsoilfoynhesesaitnvadibliylcisaohtbiensdgcurterhepad-t ia Institute o
10HkoewVevbeerc,oambseorupntrioelniacbolleumfonressttriomnagtleysbabasseodrboendXs-oruarycdeas,tahbaevlionwg resentatives of this class: the quoted value NH ∼ 1024cm−2 for f Tec
NraHy≥(a1b0o2v4ec1m0−k2e.VIn)ssupcehcctraossecso,pwye,pwrhefeenretvoeurspeorsessiublltes.fSropmechifiacrdalXly-, NenGceCo1f1N9H4c>om10e2s4fcrmom−2Xa-brasoyrdpatitoanbceololwum1n0skienVI,GwRheJ0re9a2s5t3h+e6p9re2s9- hnolog
and IGR J14175−4641 is strongly suggested by very low y
ourpreferencelistofinstrumentsisheadedbyNuSTAR–theunique o
focusinghardX-raytelescope,followedbySuzakuandthenbyall ((cid:2)0.01) X-ray/hard X-ray flux ratios that we find for them from n Ja
Swift/XRT and INTEGRAL/IBISdata. Note that we initially used n
othercurrentlyoperatingorpreviouslyflownhardX-raymissions. u
a
canFdoirdafitvees,owfethcearhreieavdiloyutobosucruorewdn(NanHal≥ysi1s0o24fcpmu−bl2i)cloybjaevcatislaabnlde itSthWeinIsdFaeTmedeJ0pa0rr2og5vue.m8d+etn6ot8b1toe8,rseaugscahardolniakcneeolytwheehreaasnvoaiullyyrcsoeedbfsrNcouumrSeTdtAhAiRsGdsNaamt,a.panlIedn, ry 31, 2
NuSTARdata(Krivonos,inpreparation).Specifically,wefittedthe theanalysisbelow,weassumethatN =3×1024cm−2 forboth 016
spectrabyasumofastronglyabsorbedpower-lawcomponent(with H
IGRJ09253+6929andIGRJ14175−4641.
ahigh-energycutoff)andadisc-reflectioncontinuummodelledwith
pexrav in XSPEC. The NuSTAR spectra of SWIFT J0025.8+6818, itseTlhfeasmaosrtedflieffictciuolnt-dcaosmeiinsattehdatsoofuNrcGeC(N493>9,1w0h25icchmm−2a)nidfuesritnedg
CGCG 420-015 and NGC 5643 are consistent with being fully H
BeppoSAX observations in 1997 (Maiolino et al. 1998), but was
reflectiondominated(i.e.dominatedbyCompton-scatteredcontin-
uum),andsoweprescribedN >1025cm−2tothem.Theothertwo foundtobeinaCompton-thinstate,withNH ∼1.5×1023cm−2,
H byXMM–Newtonin2001(Guainazzietal.2005a).Wenevertheless
objects, NGC 5728 and NGC 6240, along with strong reflection
treatNGC4939asareflection-dominatedsourceinouranalysis,
demonstrateasignificantcontributionfromtheprimarycomponent
suppressed by intrinsic absorption at the level of N ∼ 2–2.5 × in part because the hard X-ray flux measured by INTEGRAL for
1024cm−2.MorephysicallymotivatedAGNtorusmodHelsconfirmed this source is similar to that measured by BeppoSAX but lower
than the flux inferred from the XMM–Newton observation and so
this qualitative result (see Krivonos, in preparation for details).
INTEGRAL may have caught the source in a state similar to that
Our derived spectral parameters for CGCG 420-015, NGC 5643,
revealed by BeppoSAX. Generally, we adopt N = 1025cm−2 for
NGC 5728 and NGC 6240 are consistent with pre-NuSTAR esti- H
reflection-dominatedsources(thereareintotalsixsuchobjects)in
mates for these objects (Severgnini et al. 2011 ; Matt et al.2013;
ouranalysis,althoughinrealitythecolumndensityinsuchobjects
Comastrietal.2010;Vignatietal.1999,respectively).
maybeevenhigher,sayN ∼1026cm−2.
H
MNRAS454,1202–1220(2015)
ObscuredAGNfractionvs.luminosity 1205
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Wehavethusobtainedafairlylargeandhigh-quality(interms ls
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AGN. The high completeness and reliability of this sample are a/
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3 OBSERVED PROPERTIES OF LOCAL AGN ia In
s
WefirstconsideranumberofobservedpropertiesofthelocalAGN titu
populationusingourINTEGRALsample. te o
Fig. 3 shows the observed distribution of absorption columns f T
e
for our objects, while Fig. 4 shows the observed dependence of ch
n
the obscured AGN fraction on hard X-ray luminosity. The latter o
lo
wasobtainedbycountingobscuredandunobscuredsourceswithin gy
specifiedluminositybinsanddividingthefirstnumberbythesum on
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ofthetwo.Onecanclearlyseeadecliningtrendoftheobscured a
n
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AGNfractionwithincreasingluminosity,whichiswellknownfrom a
ry
previousstudies. 3
1
WenextcalculatedtheobservedhardX-rayLF,φ(Lobs)(number , 20
ofobjectsperMpc3 perlogLobs),oflocalAGN:bothinbinnedand 16
analyticform(seeFig.5).TheanalyticLFmodelusedthroughout
Figure5. Observed(intheINTEGRAL7yrsurvey)hardX-rayluminosity
thisstudyisabrokenpowerlaw:
functionoflocalAGN(filledcircles)fittedbyabrokenpowerlaw(black
dN A solidline).Thebest-fittingparametersaregiveninTable2.Forcomparison,
dloAgGLN = (L/L∗)γ1+(L/L∗)γ2. (1) theLFbasedontheSwift/BATsurvey(Ajelloetal.2012)isshownbythe
magentadashedline.
ThebinnedLFwasconstructedusingthestandard1/V method,
max
whereasthebest-fittingvalues(andtheiruncertainties)ofthechar- 7yrsurveyforagivenL ,whichcanbecalculatedfromthesky
acteristicluminosity,L∗,andofthetwoslopes,γ1 andγ2,ofthe coveragecurve(seeFig.1o)b.sThenormalizationoftheanalyticmodel
analyticmodel(seeTable2)werefoundusingamaximumlikeli- isderivedfromtheactualnumberofobjectsinthesample.
hoodestimator(similarlytoSazonovetal.2007): ComparingthisnewlydeterminedobservedhardX-rayLFwith
L=−2(cid:2)ln(cid:3) φ(Lφ(L)oVbs,i)V(mLax(L)doblso,ig)L , (2) oveurrsuosld1r5e1suolbtj(eScatsz)onoofvAeGtNal.de2t0e0c7te)dbwasiethd oINnTaEGsmRaAlLle,rwseetfi(6n6d
i obs max obs obs good agreement between the two, but the constraints on the LF
whereL aretheobservedluminositiesofAGNinoursample,and parametershavenowsignificantlyimproved.Wecanalsocompare
obs,i
V (L )isthevolumeoftheUniverseprobedbytheINTEGRAL theINTEGRALLFwiththatderivedfromastilllarger(361objects)
max obs
MNRAS454,1202–1220(2015)
1206 S.Sazonov,E.ChurazovandR.Krivonos
Table2. FitsofdifferenthardX-rayluminosityfunctionsbyabrokenpowerlaw.
AGN NAGN logL∗ γ1 γ2 Aa, Num.density Lum.density
class 10−5Mpc−3 (logL=40.5–46.5) (logL=40.5–46.5)
10−4Mpc−3 1039ergs−1Mpc−3
ObservedLF
All 151 43.74±0.19 0.93±0.10 2.33±0.15 1.122 54(41÷82) 1.57±0.20
Unobscured 67 43.98±0.32 0.83±0.18 2.37±0.28 0.243 10(7÷25) 0.45±0.08
Obscured 84 43.65±0.21 0.99±0.21 2.48±0.22 0.839 48(37÷78) 1.14±0.18
IntrinsicLF,isotropicemission,θ=30◦
All 151 43.69±0.18 0.89±0.10 2.36±0.16 1.806 61(47÷96) 1.97±0.25
Unobscured 67 43.87±0.31 0.84±0.18 2.39±0.28 0.201 7.0(5.1÷16.7) 0.30±0.05
Obscured 84 43.62±0.21 0.93±0.12 2.45±0.21 1.581 59(46÷101) 1.63±0.26
IntrinsicLF,isotropicemission,θ=45◦
All 151 43.71±0.19 0.89±0.10 2.36±0.16 1.494 52(41÷82) 1.71±0.21
Unobscured 67 43.90±0.31 0.84±0.18 2.39±0.27 0.203 7.5(5.4÷18.2) 0.32±0.06 Do
Obscured 84 43.62±0.21 0.92±0.12 2.44±0.21 1.698 59(46÷105) 1.70±0.26 wn
IntrinsicLF,cosine-lawemission,θ=30◦ loa
d
All 151 43.69±0.17 0.90±0.10 2.43±0.17 1.593 57(44÷87) 1.79±0.21 ed
Unobscured 67 43.70±0.30 0.86±0.17 2.42±0.28 0.188 5.3(3.9÷11.6) 0.19±0.03 fro
Obscured 84 43.68±0.21 0.93±0.12 2.45±0.21 1.565 66(51÷114) 1.88±0.30 hm
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bythecentralsourceinAGN.ThisobservedLFisexpectedtobeaf- n
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hardX-rayfluxandDisthedistancetothesource),thanitsintrinsic J
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likethiscanbefoundinaflux-limitedhardX-raysurveywithina ry
3
F10ig22urcem6−.2,ObbluseervfielldedhacridrcXle-sr)ayanludmoibnsocsuitryedfu(nNcHtio≥ns1o0f22uncomb−s2c,urreedd(eNmHp<ty sXm-raalylearbvsoolrupmtieono:fVthmeaxU(Lnoibvs)e/rsVemtahx(aLninittr)w≈ou(lLdobbse/Linintrt)h3e/2a.bHseenrec,ethoef 1, 201
squares)AGN,fittedbybrokenpowerlaws(bluedottedandreddashed approximationsymbolreflectsthefactthatAGNobscurationmay 6
lines,respectively).Thebest-fittingparametersaregiveninTable2. alsoaffecttheshapeofthemeasuredX-rayspectrumandthusthe
number of photons recorded by a given detector with its specific
sampleof(mostly)localAGNfoundinnearlythesameenergyband
energyresponse.Ontheotherhand,asdiscussedbelow,unobscured
(15–55keV)intheSwift/BATsurvey(Ajelloetal.2012).Ascanbe
AGNareexpectedtohavehigherobservedluminositiesthantheir
seeninFig.5,thetwoLFsareingoodagreementwitheachother.
intrinsic angular-averaged luminosities and can thus be detected
Finally,wecalculatedseparatelytheobservedLFsofunobscured
within a larger V . We can correct for both of these biases and
max
andobscuredAGN(seeFig.6).ItcanbeseenthattheseLFsare
obtainanintrinsichardX-rayLFoflocalAGN.Tothisend,weuse
differentinshape,asisverifiedbythebest-fittingparametersofthe
aphysicallymotivatedobscurationmodeldescribedbelow.
correspondinganalyticfits(seeTable2).
4 INTRINSIC PROPERTIES OF LOCAL AGN 4.1 TorusmodelandAGNspectra
TheobservedLFjustdiscussedhasnotbeencorrectedforanyef- We have a developed a Monte Carlo code for modelling AGN
fectsassociatedwithabsorptionorscatteringofhardX-raysemitted X-ray spectra modified by reprocessing in a toroidal structure of
bytheAGNcentralsourceonthewaybetweenthesourceandthe gas. The adopted geometry (see Fig. 7) is similar to that used in
MNRAS454,1202–1220(2015)
ObscuredAGNfractionvs.luminosity 1207
otherexistingmodels,e.g.Ikedaetal.(2009),Murphy&Yaqoob
(2009)andBrightman&Nandra(2011).Thekeyassumptionsof
ourmodelare:
(i) Thegeometricalshapeisthatofaringtorus.
(ii) Thegasishomogeneous,cold,neutralandofnormalcosmic
chemicalcomposition.
(iii) The X-ray spectrum emitted by the central source is a
powerlawwithanexponentialcutoff,dN/dE∝E−(cid:10)e−E/Ecut,with
(cid:10)=1.8andE =200keV.
cut
(iv) The central (point-like) source is either isotropic,
dL /d(cid:3) = const – hereafter, Model A, or emitting according
intr
toLambert’slaw,dL /d(cid:3)∝cosα,whereαistheviewingangle
intr
withrespecttotheaxisofthetorus–hereafter,ModelB.
TheintroductionofModelBisanimportantaspectofthepresent
D
studyandismotivatedbythecommonbeliefthatthehardX-ray o
w
emission observed from AGN is produced by Comptonization of n
lo
softeremissionfromanaccretiondiscaroundanSMBHinahot a
d
e
coronalyingabovethedisc.Ifsuchacoronahasquasi-planarge- d
ometry, the hard X-ray flux it produces will be collimated along fro
m
theaxisofthedisc/coronaroughlyasF∝μ(theexactlawbeing h
dependentonthephotonenergyandtheopticaldepthofthecorona; ttp
Pozdnyakov,Sobol&Sunyaev1983;Sunyaev&Titarchuk1985), ://m
n
whereμisthecosineoftheanglebetweentheoutgoingdirection ra
s
andtheaxisofthedisc/corona.Becausetheobscuringtorusinturn .ox
islikelycoalignedwiththeaccretiondisc,theemergenthardX-ray ford
radiationwillbecollimatedalongtheaxisofthetorus.Inreality,a jo
u
significantfractionofthecoronalemissionisreflectedbytheunder- rn
a
lyingaccretiondisc,butthisalsooccurspreferentiallyalongtheaxis ls.o
ofthedisc/torus(Magdziarz&Zdziarski1995).Sincethereisstill rg
a/
significantuncertaintyintheoverallphysicalpicture,weintroduce t C
taosgimetpalen,iedneeargoyf-ihnodwepsetnrodnegnltycoinlltirminastiicocnoflalicmtoartidoLninotrf/dh(cid:3)ard∝Xco-rsaαy aliforn
emissioncanaffectobservedpropertiesoflocalAGN.Wenotethat ia
possibleeffectsofanisotropicemissionontheobservedLFandob- Ins
scuredfractionofAGNhavebeenpreviouslydiscussedbyZhang titu
te
(2005)andLiuetal.(2014). o
Apart from the two alternatives for the angular dependence of f T
e
c
intrinsic emission (Model A or Model B), our model has three h
n
freeparameters:(i)theequatorialcolumndensity,NH,eq (thetotal olo
numberofHatomspercm2alonganequatoriallineofsightbetween gy
o
thecentralsourceandtheobserver,(ii)half-openingangleofthe n
J
torus,θ and(iii)theviewinganglerelativetotheaxisofthetorus, an
u
α(seeFig.7). ary
X-rayphotonsemittedbythecentralsourcecanscattermultiple 3
1
timeswithinthetorusbeforetheyeithergetphotoabsorbedinthe , 2
0
gasorescapefromthesystem.Ourradiativetransfercalculations Figure 8. Top: examples of simulated AGN spectra for Model A, half- 16
arebasedonamethoddevelopedbyChurazovetal.(2008).Thegas opening torus angle θ = 30◦ and equatorial column density NH,eq =
inthetorusisassumedtobeneutral,withtherelativeabundances 1025cm−2, for various viewing angles. The dashed curve shows the in-
ofallelementsasinthesolarphotosphere.Thefollowingprocesses trinsic(angular-averaged)spectrum.TheshadedareaindicatestheINTE-
areincludedinthesimulations:photoelectricabsorption,Rayleigh GRAL/IBISenergybandusedforAGNselectioninthiswork.Bottom:The
same,butforModelB.
and Compton scattering and fluorescence. Photoelectric absorp-
tion is calculated using the data and approximations of Verner &
Yakovlev(1995)andVerneretal.(1996).Forfluorescence,weuse Fig.8showsexamplesofemergentAGNspectrasimulatedusing
theenergiesandyieldsfromKaastra&Mewe(1993).Comptonand ourmodeloftheobscuringtorus.Asexpected,forobscuredAGN
Rayleigh scattering are modelled using differential cross-sections ( α >θ),theobservedhardX-rayfluxcanbestronglyattenuated
provided by the GLECS package (Kippen 2004 ) of theGEANT code relativetotheemittedfluxandforhighabsorptioncolumns(NH(cid:10)
(Agostinelli et al. 2003). Namely, the Livermore Evaluated Pho- 1024cm−2)thespectrumcanbecomereflectiondominated,asthe
ton Data Library (see Cullen, Perkins & Rathkopf 1990) and the observerwillmostlyseeemissionreflectedfromtheinnerwallsof
Klein–Nishinaformulaforfreeelectronsareusedtocalculatetotal thetorusratherthanemissionfromthecentralsourcetransmitted
cross-sectionsandtheangulardistributionofscatteredphotonsfor through the torus. In this last case, there also appear strong iron
eachelement. Kα and Kβ fluorescent lines at 6.4 and 7.06 keV. These spectral
MNRAS454,1202–1220(2015)
1208 S.Sazonov,E.ChurazovandR.Krivonos
propertiesandtrendsforheavilyobscuredAGNareofcoursewell
known.
WefurtherseefromFig.8thatthespectraobservedfromdirec-
tionsα<θ,correspondingtounobscuredAGN,alsodifferfromthe
intrinsic spectrum. Namely, they have an excess due to Compton
reflectionofhardX-raysfromthetorusinthedirectionoftheob-
server.Thishumpislocatedapproximatelywithintheenergyband
of 17–60 keV that we use for detecting AGN in the INTEGRAL
survey.ItisobviousthatthisComptonreflectioncomponentshould
biasobservedluminositiesofunobscuredAGNhigherinthisand
similar(e.g.Swift/BAT)hardX-raysurveys.Anyintrinsiccollima-
tionofemissionalongtheaxisoftheobscuringtoruswillmakethis
positivebiasevenstronger(seethespectrumforModelBandα≈
0inthelowerpanelofFig.8).Thisimportantaspectisfrequently
overlooked in AGN population studies, even though a reflection
D
componentiswellknowntobepresentinthehardX-rayspectraof o
w
unobscuredAGN. n
lo
a
d
e
d
4.2 AGNdetectionbias fro
m
Toquantifybiasesaffectingdetectionofunobscuredandobscured h
ttp
aAnGdNMiondethleBI,NthTeErGatRioA,LRs(NurHv,eeqy,,θw,eα)sh=owLobins/LFiingtr.,9o,fftohreMobosdeervleAd ://mn
tointrinsicluminosityinthe17–60keVenergybandasafunction ras
ofN ,foratorushalf-openingangleθ =30◦andseveralnarrow .ox
rangHes,eqoftheviewingangleα.OnecanseethatRisalwayslarger ford
Mtahfaoendweul1nA0it2y4a,ncimd.e.α−L2≈oabns0d>,RreLmiinnatcri,rnefsaosaretusanfporpobrmsocxu1irmteodat∼AelGy2Ntahs.iNsFHloe,revqeeixlnatchmreepraelseae,fstfeotror. journals.o
rg
Thistrendcanbeeasilyunderstood:theamplitudeofComptonre- a/
flectionisexpectedtobeproportionaltothetorusopticaldepth,τ, t C
cinastehe(τo(cid:10)ptic1a)l.lAysthriengarredgsimobes(cτur(cid:11)ed1A)GaNnd(cαo>nstθa),nRtidnetchreeaospespowsiitthe aliforn
–iNnHdc,rueeqea∼stoin3tghe×NrHe1,efl0qe2a4cntcedmdi−nc2ocrmaetapnsoiennaegrn-αte)q,(uaaasptaocrrotiuafllrdodmbireeacetxliopocenacsltefmodardxMuimeoutdomelthaBet ia Institute
increasingattenuationofthetransmittedcomponent.Themostob- of T
viousandimportantdifferenceofModelBwithrespecttoModelA e
c
isthattheobservedhardX-rayfluxisanisotropicevenintheab- hn
o
senceofanobscuringtorus(i.e.forNH=0)–justduetotheinitial log
collimationofemission. y o
We can proceed further and ask the question: what would be n J
a
the average observed/intrinsic flux ratio for the local populations nu
a
ofunobscuredandobscuredAGNif(i)AGNtoriwererandomly ry
orientedwithrespecttotheobserver,whichisanaturalassumption, 31
and (ii) all the tori had the same half-opening angle θ (this, of Figure9. Top:calculatedratioofobservedtointrinsic(angular-averaged) , 20
1
course, permits the physical size of the torus to vary from one luminosityinthe17–60keVenergybandforatorushalf-openingangle 6
objecttoanotherand,e.g.todependonluminosity).Tothisend, θ=30◦,fordifferentviewingangles(α),asafunctionofthetoruscolumn
wejustneedtoaveragethedependencesshowninFig.9overthe densityforModelA.Bottom:thesame,butforModelB.
viewingangleαfortheunobscuredandobscureddirections:
(cid:3) byNH,eq ∼1.5×1025cm−2 andstaysatapproximatelythislevel
Runobsc(NH,eq,θ)= c1osθR(N1H−,eqc,oθs,θα)dcosα, (3) fAoGrNhigmhoernoctoolnuimcanlldyednescitrieeass.eTshferoamver1agtoe∼ra0ti.o2RasobsNcHf,oeqrionbcsrceuarseeds
from(cid:11)1024cm−2to∼1.5×1025cm−2andstaysatthislevelthere-
Robsc(NH,eq,θ)= (cid:3)0cosθR(NHc,eoqs,θθ,α)dcosα . (4) aqofubtaseclri.utarIentidvtehdleyircesacimstieoilnoasfr,aibsucmtostohirneeec-ploarnowtnraoesumtnibctteeitdnw:geisetoniustrhcpeer,eustnheonebtssaictluurreaeatiddoynanaidst
The result is shown in Fig. 10 as a function of N for torus N = 0 and increases further, due to Compton reflection, with
H,eq H
half-opening angles θ = 30◦, 45◦ and 60◦. One can see that increasingN .
H
for Model A, R (the average observed/intrinsic flux ratio ItisobviousfromFig.10thatahardX-raysurvey,liketheones
unobsc
for unobscured AGN) reaches a maximum of ∼1.5–2, depend- performed by INTEGRAL and Swift, will find unobscured AGN
ing on θ, at N ∼ 5 × 1024cm−2, then declines to ∼1.4–1.7 more easily than even lightly obscured objects, let along heavily
H,eq
MNRAS454,1202–1220(2015)
ObscuredAGNfractionvs.luminosity 1209
torus.GiventhefairlysmallnumberofobscuredAGN,especially
of heavily obscured ones, in our sample, we are bound to make
somesimplifyingassumptions.Forexample,wemayassumethat
the intrinsic N distribution does not depend on luminosity. In
H,eq
this case, the intrinsic N distribution can be estimated simply
H,eq
bydividingtheobservedonebyRo3b/s2c(NH,eq,θ)(andnormalizing
theresultingdependencesothatitsintegraloverN equalsunity),
H
with the bias factor R = L /L having been discussed in
obsc obs intr
Section4.2.
In doing this exercise, we assumed that NH,eq=(4/π)NH≈
1.27N for our obscured AGN. This is because we do not know
H
the orientation of our objects apart from the fact that some of
themareunobscuredandhenceα <θ,whileothersareobscured
and hence α > θ. For our assumed torus geometry (see Fig. 7),
theline-of-sightcolumndensitydependsontheviewingangleas
D
follows: o
(cid:4) w
(cid:5) (cid:6) n
cosα 2 lo
NH(α)=NH,eq 1− cosθ , (5) aded
sothatthemeanN overallobscureddirectionsis fro
H m
NH,obsc= (cid:3)0cosθNcHo(sαθ)dcosα = π4NH,eq. (6) http://m
n
Hence,thecoefficientintheconversionofN toN above.Note ra
that the NH values adopted from the literaHture foHr,eqsome of our s.oxfo
Compton-thick AGN may already have been ascribed the mean- rd
ingofanequatorialratherthanline-of-sightcolumndensitybythe jou
correspondingauthors.However,consideringoursampleofheav- rna
ilyobscuredsourcesasawhole,theinformationitcontainsonthe ls.o
absorptioncolumnsisveryheterogeneous,asitisbasedonvarious arg/
spectralmodelsusedbyvariousauthors.Fortunately,atypicalex- t C
∼pe2c0tepdedricfefnerte(nsceeebeeqtuwaetieonnN6Ha,ebqoavned)NanHdfohrasobnsecgulrigedibAleGimNpiascotnolyn aliforn
ourresults. ia In
TheresultingintrinsicN distributionispresentedinFig.11. s
It is only weakly dependeHn,etqon both the assumed half-opening titu
te
angle θ of the obscuring torus and the assumed emission model o
(ModelAorModelB).Thisdistributioncanberoughlydescribed f Te
as log-uniform between NH,eq = 1022 and 1026cm−2, although chn
o
the upper boundary is, of course, fairly uncertain. A similar re- lo
g
sultwaspreviouslyobtainedusingAGNfromtheSwift/BAThard y
o
X-raysurvey(Burlonetal.2011;Uedaetal.2014).Moreover,the n J
a
intrinsicN distributionshowninFig.11issimilartotheonein- n
H u
a
ferredforopticallyselectedSeyfert2galaxies(Risaliti,Maiolino& ry
Salvati1999). 31
, 2
0
1
6
Figure10. Top:calculatedratioofobservedtointrinsic(angular-averaged)
4.4 Intrinsicluminosityfunction
luminosityinthe17–60keVenergybandaveragedseparatelyoverallun-
obscuredandobscureddirections(α<θandα>θ,respectively)forthree We now calculate the intrinsic hard X-ray LF of unobscured and
valuesofthetorushalf-openingangle,asafunctionofthetoruscolumn obscuredAGN,φ(L )≡dN/dlogL .AsfortheobservedLFs
intr intr
density,forModelA.Bottom:thesame,butforModelB. discussedinSection3,weusebothbinnedandanalyticrepresenta-
tions.
obscuredones.Ourgoalnowistocorrecttheobservedstatistical
ForthebinnedLFs,theprocedureisasfollows:
propertiesoflocalAGNforthisobviousbias.
(i) First, based on the observed luminosity L and estimated
obs,i
torus column density N of each source in the sample (Ta-
4.3 Intrinsicdistributionoftoruscolumndensities H,eq,i
bleA1),wedetermineitsintrinsichardX-rayluminosityaseither
Wecanfirstestimatetheintrinsicdistributionofthecolumnden- L = L /R (N , θ) (for unobscured sources) or L
intr,i obs,i unobsc H,eq,i intr,i
sities,N ,ofAGNtorii.Tothisend,weneedtocorrecttheob- = L /R (N , θ) (for obscured sources), where the ratios
H,eq obs,i obsc H,eq,i
servedN distribution(Fig.3)forabsorptionbias,excludingfrom R and R are calculated as discussed above (from equa-
H unobsc obsc
the consideration the first, N < 1022cm−2, bin since it pertains tions3and4,seeFig.10),assumingsome(thesameforallobjects)
H
tounobscuredAGNforwhichourlineofsightdoesnotcrossthe torushalf-openingangleθ andusingModelAorModelB.Here
MNRAS454,1202–1220(2015)
1210 S.Sazonov,E.ChurazovandR.Krivonos
Aswassaidbefore,theN valuesforourobscuredobjectsare
H,eq
estimated from their measured N columns as N = 1.27N .
H H,eq H
However,wecannotdeterminesimilarlythetoruscolumndensities
forourunobscuredAGN.1Therefore,wesimplyassumethatN
H,eq
=1024cm−2 fortheseobjects,sincethisisapproximatelytheme-
dianvalueoftheinferredintrinsicabsorptioncolumndistribution
forobscuredAGN(seeFig.11).
(ii) Secondly, we calculate for each source the volume of the
Universe,V (L ),overwhichAGNwithsuchobservedlumi-
max,i obs,i
nositycanbedetectedintheINTEGRALsurvey.Sincethedetection
limitforagivenhardX-rayinstrument(IBISinourcase)isactu-
allydeterminedbyphotoncounts,itshoulddependontheobserved
X-rayspectralshape,whichfortheproblemathandisaffectedby
absorptionandreflectioninthetorus(seeexamplesofAGNspectra
inFig.8).WecorrectV forthiseffect,butthiscorrectionproves
max,i
D
tobenegligible(asisthek-correctionduetocosmologicalredshift). o
w
Asaresult,weobtainessentiallythesameVmax,iforoursourcesas nlo
weusedinconstructingtheobservedLFinSection3. a
d
(iii) The final step consists of summing up the 1/V contri- ed
butionsoftheindividualsources,i.e.addingthe1/V max,fioreach fro
max,i m
AGNofagivenclass(unobscuredorobscured)tothespacedensity h
ofsuchobjectswithinaluminositybincontainingL (ratherthan ttp
L )forthissource. intr,i ://m
obs,i n
ra
ToobtainanalyticformsoftheintrinsicLFs,weusethesamebroken s.o
x
power-lawmodelasforourobservedLFsbutadifferentlikelihood fo
eLst=im−at2or(cid:2):i ln(cid:3) (cid:3) φφ((LLiinnttrr),iV)m(cid:3)axV(mLaixnt(rL,NintHr,i,e,qN)dH,leoqg)dLliontgrdNloHg,eqNH,eq. rdjournals.org
(7) a/
t C
HouerreobLjienctrt,isaarsewtheeussaemdebeefsotriemtaotecsonosftrtuhcetitnhteribnisnicnelduminitnroinssitiicesLFosf aliforn
o(ib.es.cucraelcduAlaGteNdafrnodmasLsuobms,iinugsitnhgattNhe act=ua1l0N24Hc,ime−st2imfoartethsefournothbe- ia Ins
scuredones),butV (L ,N )iHs,enqowthevolumeoverwhich titu
max intr H,eq te
AGNwithgivenintrinsicluminosityL andtoruscolumndensity o
NvoHl,ueqmceasn,wbeedaegtaeicnteudsienththeeαIN-aTvEerGagReAdiLntqrsuuarnvteiyti.eTsoRcunaolbcsuc(laθt,eNthHe,esqe) f Techn
(infittingtheintrinsicLFofunobscuredAGN)andRobsc(θ,NH,eq) olog
(in fitting the intrinsic LF of obscured AGN). The integrals over y
o
dlogNH,eq in equation (7) are computed from 1022 to 1026cm−2, n J
a
i.e.weassumethattheintrinsicdistributionoftoruscolumndensi- n
u
a
tiesislog-uniformoverthisrange,assuggestedbytheresultofour ry
preceedinganalysisshowninFig.11. 31
Fig. 12 shows the resulting intrinsic LFs for unobscured and , 2
0
obscured AGN, calculated assuming θ = 30◦ for Model A and 16
Figure11. Reconstructedintrinsicdistributionofcolumndensitiesofob-
scuringtoriinlocalAGN,calculatedassumingθ=30◦andeitherModelA ModelB.Weseethatintheformercase,theshapesoftheintrinsic
LFs of unobscured and obscured AGN are clearly different from
(top)orModelB(bottom).Thedottedlinecorrespondstoalog-uniform
distribution. eachother,althoughtoalesserdegreethatitwasfortheobserved
LFs (Fig. 6) from which they derive. However, for Model B the
intrinsicLFsofunobscuredandobscuredAGNarenotsignificantly
again we use the average ratios Runobsc and Robsc rather than the differentinshapefromeachother.Theseconclusionsareverified
viewing-angledependentR(NH,eq,θ,α)fromwhichtheyderivefor bythebest-fittingparametersobtainedfortheseLFs(seeTable2).
the lack of knowledge of the orientation of our objects. Strictly NotethatthederivedintrinsicLFs(bothbinnedandanalyticones)
speaking,thisprocedureisnotfullycorrect,becauseforgivenN
H,eq
and θ, a hard X-ray flux-limited survey will preferentially find
objects with smaller viewing angles α within the corresponding
groupsofα<θ andα>θ,asisclearfromFig.9.However,this 1Inprinciple,onecouldtrytoestimateNH,eqforunobscuredAGNfromthe
contributionofthereflectioncomponenttotheobservedspectrum,butthat
mayberegardedasanext-ordercorrectiontothebiasconsidered requireshigh-qualityhardX-raydata,whichisnotalwaysavailable,and
here and does not significantly affect our results, as we verify in ismodeldependent.Inparticular,theresultwilldependontheunknown
Section5. openingangleθ.
MNRAS454,1202–1220(2015)
ObscuredAGNfractionvs.luminosity 1211
(ii)eachobscuredAGNfromtheINTEGRALsamplemovesitsown
distancetotheright-handsideoftheplot,thisshiftbeingsmallfor
lightly obscured objects (N < 1024cm−2) but substantial (up to
H
logL /L ∼1forN (cid:3)1025cm−2)forheavilyobscuredones.
intr obs H
Finally,wecancalculatetheintrinsicLFoftheentirelocalAGN
population, by summing up the contributions of unobscured and
obscuredsources.Inobtainingtheanalyticfitinthiscase,wedefine
V (L ,N )asfollows:
max intr H,eq
Vmax=Vmax,unobsc(1−cosθ)+Vmax,obsccosθ, (8)
whereV (L ,N )andV (L ,N )arethecorre-
max,unobsc intr H,eq max,obsc intr H,eq
spondingvolumesforunobscuredandobscuredAGN.Theresulting
LFisshowninFig.13anditsbest-fittingparametersarepresented
inTable2.
OnecanseethatthetotalintrinsicLFisnotverydifferentfrom
D
thetotalobservedLF.Thismeansthatthetwoeffectsobservedin o
w
Fig. 12, namely the shift of the LF of unobscured AGN to lower n
lo
luminosities and the shift of the LF of obscured AGN to higher ad
e
luminosities almost compensate each other, with this conclusion d
beingonlyweaklysensitivetotheassumedtorusopeningangleand fro
m
angulardependenceofintrinsicemission. h
ttp
://m
4.5 TotalAGNspacedensity n
ra
s
Integration of the total intrinsic and observed LFs over luminos- .ox
itysuggeststhatthecumulativehardX-rayluminositydensityof ford
local AGN may be underestimated by the observed LF by ∼10– jo
u
30percent,althoughthisincreaseisstatisticallyinsignificant(see rn
a
Table2).Specifically,theintrinsicluminositydensityofAGNwith ls.o
L >1040.5ergs−1isfoundtobe∼1.8×1039ergs−1Mpc−3(17– rg
intr a/
60keV),withtheexactvalueslightlydependingonourassumptions t C
(seFeoTrable2o)u.r assumed intrinsic AGN spectrum aliforn
(dN/dE∝E−1.8e−E/200keV), the ratio of luminosities in the ia
2–10 and 17–60 keV energy bands is about unity. Therefore, the Ins
luminosity density of AGN with L > 1040.5 erg s−1 may be titu
estimatedat∼1.8×1039ergs−1Mpicn−tr3alsointhestandardX-ray te o
band(2–10keV).Wemaycomparethisvaluewithapredictionfor f T
e
z=0basedonaredshift-dependentintrinsicLFderivedbyUeda ch
n
o
etal.(2014)usingalargeheterogenoussampleofAGNcompiled lo
g
from various surveys. Integration of this LF over the luminosity y
rangefrom1040.5to1046.5ergs−1gives∼8×1038ergs−1Mpc−3 on
J
(2–10 keV), which is a factor of ∼2 smaller than the above an
u
estimate.Inreality,theLintr(17–60keV)/Lintr(2–10keV)ratiomay ary
wellbe∼1.5ratherthan∼1duetotheexpectedpresenceinAGN 3
1
spectra of a Compton reflection component associated with the , 2
0
Figure12. Top:reconstructedintrinsichardX-rayLFsofunobscured(blue accretion disc. In fact, this component was already discussed in 16
filledcircles)andobscured(redemptysquares)AGN,fittedbyabroken Section4.1asoneofthereasonswhyhardX-rayemissionmaybe
power law (the best-fitting parameters are given in Table 2; blue dotted intrinsicallycollimatedinAGNandisimplicitlytakenintoaccount
lineandreddashedline,respectively).ModelAisadopted,withθ =30◦. in our anisotropic Model B. Taking this spectral component into
Bottom:thesame,butforModelB. account, we can lower our estimate of the luminosity density to
∼1.2×1039ergs−1Mpc−3(2–10keV),whichisstillhigherthan
are only weakly sensitive to the torus half-opening angle θ that the Ueda et al. (2014) result by a factor of ∼1.5. The remaining
wasassumedinconstructingthem,andnearlythesameresultsare differencemayberelatedtothedifferentproceduresusedinthese
obtainedforθ=30◦andθ=45◦.Thisisduetotheweaksensitivity works to construct the intrinsic LFs and to the larger and more
oftheR andR factorstoθ (seeFig.10). completesampleoflocalheavilyobscuredAGNusedinourstudy.
unobsc obsc
The transformation of the observed binned LFs to the intrinsic
onescanbeunderstoodasfollows:(i)allunobscuredAGNmaking
4.6 IntrinsicdependenceofobscuredAGNfraction
uptheLFshiftbythesameamount,logL /L ∼0.1and∼0.3for
obs intr onluminosity
ModelAandModelB,respectively,totheleftalongtheluminosity
axis(sincewehaveassumedthesameequatorialopticaldepthof SimilarlytotheobservedLF,theobserveddependenceofthefrac-
thetorus,N =1024cm−2,forallofourunobscuredobjects),and tionofobscuredAGNonluminosity(Fig.4)mustbeaffectedby
H,eq
MNRAS454,1202–1220(2015)