Heavily reddened type 1 quasars at z > 2 I: Evidence for significant obscured black-hole growth at the highest quasar luminosities

1.5 MB·English

by  Manda Banerji

Mon.Not.R.Astron.Soc.000,000–000(0000) Printed6January2015 (MNLATEXstylefilev2.2)
Heavily Reddened Type 1 Quasars at z > 2 I: Evidence for
Significant Obscured Black-Hole Growth at the Highest Quasar
Luminosities
5
1 Manda Banerji1,2,3⋆, S. Alaghband-Zadeh2,3, Paul C. Hewett2, Richard G. McMahon2,3
0
2
1DepartmentofPhysics&Astronomy,UniversityCollegeLondon,GowerStreet,LondonWC1E6BT,UK.

n 2InstituteofAstronomy,UniversityofCambridge,MadingleyRoad,Cambridge,CB30HA,UK.
a 3KavliInstituteforCosmology,UniversityofCambridge,MadingleyRoad,Cambridge,CB30HA,UK.
J

5

] 6January2015
A
G
. ABSTRACT
h
p
We present a new population of z > 2 dust-reddened, Type 1 quasars with 0.5 .
o- E(B − V) . 1.5, selected using near infra-red (NIR) imaging data from the UKIDSS-
r LAS, ESO-VHS and WISE surveys. NIR spectra obtained using the Very Large Telescope
t
s (VLT) for 24 new objects bring our total sample of spectroscopically confirmed hyperlu-
a minous (>1013L ), high-redshift dusty quasars to 38. There is no evidence for reddened
⊙
[ quasars having significantly different Hα equivalentwidths relative to unobscured quasars.

1 The average black-hole masses (∼109-1010M⊙) and bolometric luminosities (∼1047 erg/s)
v are comparable to the most luminous unobscured quasars at the same redshift, but with a
5 tail extending to very high luminosities of ∼1048 erg/s. Sixty-six per cent of the reddened
1 quasarsare detected at > 3σ at 22µm by WISE. The average6µm rest-frameluminosity is
8 log10(L6µm/erg s−1)=47.1±0.4,making the objects among the mid-infraredbrightest AGN
0 currently known. The extinction-corrected space-density estimate now extends over three
0 magnitudes(−30<M <−27)anddemonstratesthatthereddenedquasarluminosityfunc-
i
1. tion is significantly flatter than that of the unobscured quasar population at z = 2−3. At
0 the brightest magnitudes, M . −29, the space density of our dust-reddened population
i
5 exceeds that of unobscured quasars. A model where the probability that a quasar becomes
1 dust-reddenedincreasesathighluminosityisconsistentwiththeobservationsandsuchade-
v: pendencecouldbeexplainedbyanincreaseinluminosityandextinctionduringAGN-fuelling
i phases.ThepropertiesofourobscuredType1quasarsaredistinctfromtheheavilyobscured,
X
Compton-thickAGNthathavebeenidentifiedatmuchfainterluminositiesandweconclude
r thattheylikelycorrespondtoabriefevolutionaryphaseinmassivegalaxyformation.
a
Keywords: galaxies:active,(galaxies:)quasars:emissionlines,(galaxies:)quasars:general,
(galaxies:)quasars:individual
1 INTRODUCTION 2012). However, thesesurveys donot distinguish between a cen-
trally concentrated obscuring medium, on parsec scales, close to
Luminous dust-obscured quasars have been postulated to repre-
the black-hole accretion disk (Urry&Padovani 1995; Antonucci
sent the missing evolutionary link between merger-induced star-
1993),and larger-scaleobscuration due togasanddust clouds in
burst galaxies and ultraviolet (UV) bright quasars (Sandersetal.
thequasar hostgalaxy(Mart´ınez-Sansigreetal.2005).Mosthard
1988)intheoreticalmodelsofgalaxyformation(e.g.Hopkinsetal.
X-rayandmid-infraredsurveys(e.g.withtheSpitzerSpaceTele-
2008; Narayananetal. 2010). Samples of obscured active galac-
scope)havecoveredrelativelysmallareasofsky,probingobscured
ticnuclei (AGN) have been selected both in the hard X-ray (e.g.
black-holegrowthinrelativelylow-luminosityAGN,althoughthe
Brusaetal.2010;Civanoetal.2012;LaMassaetal.2013)andthe
situation is now changing at mid infrared wavelengths with data
mid-infrared(e.g.Sternetal.2012;Assefetal.2013;Donleyetal.
fromtheWISEAll-SkySurvey(Wrightetal.2010).Inthesefaint
samples, the number of obscured AGN isfound todecrease with
increasingluminosity. Constraintsonobscuredblack-holegrowth
⋆ E-mail:[email protected] atthehighestquasarluminositieshoweverremainhighlyuncertain
(cid:13)c 0000RAS
2 M. Banerjiet al.
andtherelationshipbetweenhyperluminous(>1013L⊙)obscured theselectionofmuchmorehighlyobscuredAGN.TheAGNthat
quasarsandthenowwell-studiedobscuredAGNatlowluminosi- havesofarbeenidentifiedbyWISEareseentobeComptonthick
tiesisalsouncertain. (Sternetal.2014).Broademissionlinesoriginatingfromgasclose
X-ray surveys also show a curious lack of high Eddington totheblack-holearethereforecompletelyconcealedandestimating
ratio (L/L > 0.1) objects with N between 3×1021 and virialblack-holemassesisnolongerpossible.
Edd H
3×1022 cm−2 (Fabian2012;Raimundoetal.2010).Objectswith The wide-field NIR UKIDSS Large Area Survey (LAS)
such properties, i.e. high luminosity combined with a significant (Lawrenceetal. 2007) and VISTA Hemisphere Survey (VHS;
gas/dustcolumn,couldpossessmassiveAGN-drivenoutflows.The McMahonetal.2013)allowustoprobemuchfainterthanwaspos-
apparentupperlimittothedistributionofEddingtonratioscouldbe sible using 2MASS and enable selection of complementary sam-
aselectionbias,asmostX-raysurveysdonotcoveralargeenough ples of obscured quasars to the WISE survey. In a survey over
area to detect the rarest and brightest quasars with high Edding- >1000deg2oftheUKIDSSandVHSdatawewereabletoidentify
ton ratios. Such objects have traditionally been selected through apopulationofz∼2−3,E(B−V)∼0.8quasars(Banerjietal.
theirrest-frameUVemissionwhichisverysensitivetodustextinc- 2012, 2013 - hereafter B12and B13respectively), demonstrating
tionandthereforebiasedagainstdetectingluminousquasarswith thatcontaminantpopulationscanbeeliminatedwithouthavingto
even moderate gas column densities. The Sloan Digital Sky Sur- relyonradio pre-selection. Our new quasars areamong themost
vey (SDSS)DataRelease(DR) 7quasar sample (Schneideretal. bolometrically luminous quasars known (L >1047 erg/s) but,
bol
2010) now mitigates the situation to a degree. The flux limit in asaresult of their significant dust-extinctions, areoften invisible
the redder i-band allows some intrinsically very luminous ob- inwide-field optical surveys like SDSS.Thesample represents a
jectswithE(B−V) ≃0.5tobeincluded(Richardsetal.2003). populationofhyperluminousquasarsatz ∼ 2−3whoseextinc-
The new SDSS-IIIBOSS DR10 quasar survey (Paˆrisetal. 2014) tion properties are intermediate between UV-selected, essentially
reachesfainteropticalmagnitudesthantheSDSSandhassignifi- unobscured,quasarsandtheveryheavilyobscuredAGNemerging
cantlyincreased thenumber of quasars known at themainepoch fromWISE.Similarobscuredluminousquasarsshowingstrongev-
of galaxy formation at z ∼ 2 − 3. Populations of red quasars idenceforcorrespondingtotheAGNfeedbackphase,arealsonow
aredetectedintheBOSSdata(Rossetal.2014)includingthefirst emergingfrommulti-wavelengthdegree-scalegalaxysurveyssuch
largesampleofnarrow-lineType2obscured quasarsathighred- asCOSMOS(Brusaetal.2010;Bongiornoetal.2014;Brusaetal.
shifts(Alexandroffetal.2013),someofwhichalsoshowevidence 2014).IndeedthebrightestobscuredquasarselectedfromtheCOS-
forbroad-linesinthenearinfrared(Greeneetal.2014).However, MOSsurveyisthefaintestobscured quasar selectedinourwide-
even with the fainter flux-limit, BOSS cannot find quasars with fieldUKIDSSsearchforsimilarobjects(B12).Theabilitytoiso-
E(B−V)&0.6. latetheluminousAGNpopulationwithintermediatelevelsofex-
Wide-fieldinfraredsurveysnowcovermuchoftheobservable tinction means that it is now possible to investigate objects with
sky,providingthesensitivitytodetectdusty,intrinsicallyluminous, extinctionscorrespondingtoreddeningsof0 . E(B−V) . 3.
broad-linequasars.The2MASSsurveyhasidentifiedopticallyob- Newinsight intotheimportanceofnon-spherical geometries(i.e.
scured quasars that are also radio-loud (e.g. Glikmanetal. 2007; ‘unifiedschemes’)andevolution,involvingspecificphasesduring
Urrutiaetal.2009;Glikmanetal.2012);theradioselectionusing AGNlifetimes,forexplainingthedistributionofextinctionproper-
FIRSTdataisnecessarytoeliminatecontaminantpopulationsbut tiescanbeexpected.
meansthatthemajorityofAGNareexcludedbytheselection.In Our survey also led to the identification of the prototype
radio-loud red quasars (e.g. Websteretal. 1995), the red colours quasar:ULASJ1234+0907,thereddestbroad-linequasarcurrently
canariseasaresultof thepresence of aredsynchrotron compo- known. With an Eddington ratio of 0.65 (B12) and a neutral
nent (Francisetal. 2001; Whitingetal. 2001) rather than due to hydrogen column-density of 9×1021 cm−2 (Banerjietal. 2014),
dust.Theflux-limitofthe2MASSsurveyhasalsomeantthatthese ULASJ1234+0907liesinthesparsley-populatedhighL/L and
Edd
redquasarsarepredominantlyatlow-redshiftalthoughwithsome intermediategas column regimefound fromthe statisticsof hard
of the most luminous quasars seen out to z > 2 (Glikmanetal. X-raysources. Among themost luminous quasars known atboth
2012). A concern at low-redshifts is that host galaxy contamina- X-rayandfar-infraredwavelengths,ULASJ1234+0907mayrepre-
tioncanreddentheobservedcoloursofthesequasars.Thegalaxy senttheemergingphaseofasupermassiveblack-holeshortlyafter
spectralenergydistribution(SED)peaksat∼1µm,corresponding astarburst (Banerjietal. 2014). Larger surveys for NIR-selected,
totheinflectionpointintheAGNSED.ThisfeatureisintheNIR dust-obscured, luminous quasars may unearth more objects like
JHK filters at z ∼ 0.2 − 1. However, at z ∼0.7, the FIRST- ULASJ1234+0907.
2MASSredquasarsareseentobeassociatedwithmerginggalaxy The current paper presents a much larger survey for heavily
hosts(Urrutiaetal.2008),consistentwithaninterpretationwhere dust-reddened, hyperluminous broad-line quasars at z = 2−3,
theobjects arein atransitionphase fromstarburst tounobscured where the abundance of gas-rich, star-forming galaxies provides
quasar.Extendingtheseinvestigationstofocusonthemainepoch anatural explanation for thepresence of extended obscuring me-
of galaxy and black-hole formation at z ∼ 2−3 will be in in- diaintheseluminousquasars.Combinedwithobjectspresentedin
structiveinunderstandingtheimportanceofthisobscuredphasein B12 and B13, the new sample allows us to characterise in detail
galaxyformation. the demographics of the luminous reddened quasar population at
The WISE All-Sky Survey operating at mid-infrared wave- z ∼ 2.5,includingthedirectcalculationofthespacedensityover
lengths,hasrecentlyledtotheidentificationofanewpopulationof athree-magnitudeinterval.Weemphasisethattheparameterspace
hyperluminousdust-obscuredgalaxies(HyLIRGs),whosespectral sampledbyoursurveyisverydifferentfromthatofX-raysurveys
energydistributions(SEDs)areconsistentwithadominantcontri- for obscured AGN in deep fields covering only a few square de-
bution from AGN (Eisenhardtetal. 2012; Wuetal. 2012). These grees.Acompanionpaper(Alaghband-Zadehetal.,inpreparation)
HyLIRGsarealsopostulatedtorepresenttheevolutionarylinkbe- investigatesthespatiallyresolved properties of thenew reddened
tweenmassivestarburstsandluminousquasars.TheWISEsamples quasarsfromtheIFUdatapresentedhere.
arecomplementarytonearinfraredselectedsamplesastheyenable Thestructureofthepaperisasfollows.First,theobservational
(cid:13)c 0000RAS,MNRAS000,000–000
HeavilyReddenedType 1Quasarsatz > 2 3
data,includingthephotometricselection(Section2)andspectro- stratewhichobject populations areeliminatedbytheoptical cuts
scopic follow-up (Section 3), is described. The generation of the andtodeterminewhatthecontaminantsmaybeinregionswhere
key physical properties of the quasars, including extinction esti- we do not yet have optical coverage. Our selection produced 10
mates,luminositiesandblack-holemasses,iscoveredinSection4, candidatesdowntoafluxlimitofK <18.8over129deg2,af-
AB
priortoconsiderationoftheobjectpropertiesderivedfromWISE tervisualinspectiontoremovespuriousandblendedsources.Two
photometricdatainSection5.Theprimaryscientificresult,thecal- of the 10, ULASJ2150−0055 and ULASJ2224−0015, were ob-
culationofthepopulationspacedensityandluminosityfunctionis servedaspartofthesampledescribedinB12.Onemorecandidate
presentedinSection6,followedbyasummaryofthemainresults (SDSSJ211805.27+010344.7)hasanopticalspectrumfromSDSS
inSection7.Throughout thepaperweassumeaflatΛCDMcos- whereitisclassifiedasaz ∼ 5quasar,althoughwithlowconfi-
mologywithh =0.70,Ω = 0.30andΩ =0.70.TheVHSmag- dence.Theopticalspectrumdoesnotshow anyobviousemission
0 m Λ
nitudesareontheABsystemwheretheconversionsfromVegato lines.Theremainingsevensourceswereaddedtoourspectroscopic
ABusedare:J = +0.937,H = +1.384,K = 1.839.AllWISE targetlist.
magnitudesandcoloursareontheVegasystem. • The VHS-DES SPT Region: In this region (20h<RA<0h,
−60◦ < DEC < −45◦) we identify a total of 29 candidates
down to a flux limit of K < 18.8 over 498deg2. In addi-
AB
tion, over the 83deg2 area of the ‘SPT Deep Field’ (centred at
2 PHOTOMETRICSELECTION
23h<RA<00hand−60◦ <DEC <−50◦),theselectionwasex-
2.1 ColourSelectionofReddenedQuasars tendedtoK <19.3,givingfouradditionalcandidates.TheSPT
AB
Wemake use of new wide-fieldinfraredphotometry over ∼1500 DeepFieldbenefitsfrommulti-wavelengthcoveragefromSpitzer
(Ashbyetal. 2013), Herschel and XMM-Newton, which can be
deg2fromVHSandWISE,inordertoidentifyluminousreddened
usedtoinvestigatethemulti-wavelengthpropertiesofourquasars.
quasarcandidatesinthesouthernhemisphere.Inaddition,wealso
use>3000deg2ofimagingdatafromtheUKIDSSLargeAreaSur- • TheVHS-ATLASSGCRegion:InthisregioncoveredbyVHS
vey (LAS) (Lawrenceetal. 2007) in the northern hemisphere, to (20h<RA<0h, −20◦ < DEC < −2◦) weonlyselected candi-
selectasampleofthereddestquasars,suchasULASJ1234+0907 dates over the ∼488deg2 area with optical photometry from the
(Banerjietal. 2014). Thedetails of the colour selection has been SDSS.TheVHS-ATLASregionshaveshallowerJ-bandcoverage
presentedinB13butweprovideasummaryhere.Candidatesmust compared to VHS-DES (McMahonetal. 2013) and the selection
bemorphologicallyclassifiedaspointsourcesintheK-band(i.e. ofcandidateswithextremelyred(J−K)coloursispronetocon-
withkclass = −1;Gonza´lez-Solaresetal.2011)andpossessex- taminationfromlargernumbersofspurioussources.However,un-
tremelyredNIRcoloursof(J−K) >1.6.Themorphologycut liketheVHS-DESregion,VHS-ATLASalsobenefitsfromY-band
AB
isnecessarytoensurethatweisolateapopulationofquasarsathigh coverage, which we used to impose an additional selection crite-
redshiftscorresponding tothepeakepochofblack-holeaccretion rion: Y > J. Three candidates were selected and verified to be
activity, where the host galaxy light in the NIR is sub-dominant. faintandredatopticalwavelengthsbasedontheSDSSdata.
TheredcoloursofthesequasarsintheNIR,canthenbeattributed • The VHS-ATLAS NGC Region: This region
todust-reddening ratherthangalaxystarlight.AWISE colour-cut (13h40<RA<16h20 and −20◦ < DEC < −2◦) encom-
of(W1−W2) > 0.85 isthenappliedtoseparatequasarsfrom passes the area used for target selection in our pilot survey
stars. Candidates are required to be detected at asignal-to-noise- (B13).NinebrighttargetswithK < 18.4wereselectedfrom
AB
ratio(S/N)of>5inboththeWISEW1andW2bands.Asshown 421deg2. Two of which, VHSJ1350-0503 and VHSJ1409-0830,
inB13,thisselectionisextremelyeffectiveinisolatingrarepopu- wereobservedinB13.Theremainingsevencandidateswereadded
lationsofheavilyreddenedquasarsathighredshifts. toourspectroscopictargetlist.
Our quasar sample encompasses several different survey re- • The UKIDSS-LAS Data Release 10 (H −K) > 1.4 Sam-
gions. Below we describe the candidate selection criteria used in ple:Finally,usingtheUKIDSS-LASDR10,coveringatotalarea
each of these regions as well as ancillary multi-wavelength data of3131deg2 atDEC<20◦ (observablefromtheVeryLargeTele-
thatwereusedtoprioritisetargetsforspectroscopy.Afterapplying scope),wealsoconstructedacandidatelistofthereddestquasars
thecolourandmorphologyselectionsineachofoursurveyareas, which satisfy the additional colour selection criterion of (H −
allcandidateswerevisuallyinspectedinordertoremovespurious K) > 1.4 and have K < 18.9. These would correspond to
sources.Themostcommonsuchspurioussourcesareinstancesof the dustiest hyperluminous quasars at these high redshifts with
close neighbours in the VHS data with separations of <3arcsec E(B−V) & 1.2andtheobjectivewastofindmorequasarslike
andwheretheWISEphotometryappearstobeblended,makingthe ULASJ1234+0907(Banerjietal.2014).Threeoftheseextremely
WISEcoloursunreliable.Thesurveyregions,selectioncriteriaand red candidates were visible at the time of observations and were
numberofcandidatesaresummarisedinTable1. alsoaddedtoourspectroscopictargetlist.
• The VHS-DES Stripe82 Region: This region (20h<RA<0h,
−2◦ <DEC <2◦)overlapstheSDSSStripe82multi-epochsur-
veywherethecoaddeddatareaches≃2magfainterthanthemain
SDSSsurvey(Annisetal.2011).AsdiscussedinB12,weusedthe
deepcoaddSDSSStripe82photometrytoselectonlythesubsetof Ourfinalcandidatelistcomprisedatotalof53spectroscopic
red(J−K)candidatesthatarealsofaintandredatopticalwave- targets,excludingcandidatesalreadyobservedbyB12andB13.As
lengths.Candidateswerethereforerequiredtosatisfytheadditional described below, 48 of these targets were successfully observed,
selectioncriteria:i >20.5and(i−K) >2.5. with24classifiedasbroad-linequasars.Thecandidatelistincludes
AB AB
Manyofourinfrared-selectedcandidatesthatfailedthiscutand a complete sample of 41 objects, with K < 18.9, over a re-
AB
are blue and bright in the optical, possess SDSS or BOSS spec- gion of 1115deg2, selected toprovide quantitative constraints on
tra. Later, in Section 2.2, we show the SDSS spectra to demon- thespacedensityofthereddenedquasarpopulation.
(cid:13)c 0000RAS,MNRAS000,000–000
4 M. Banerjiet al.
Table1.SummaryofsurveyregionsandselectioncriteriaforreddenedquasarspresentedinthisworkplusB12andB13.Severalsurveyregionsarespectro-
scopicallyincomplete.Column4givesthenumberofcandidatesobserved,withthetotalnumberofcandidatesandthepercentagecompletnessinbrackets.
Column5givesthecorrespondinginformationforthenumberofcandidatesyieldingspectroscopicredshifts,withthetotalnumberofspectroscopictargets
andthepercentageredshiftyieldinbrackets.
SurveyRegion SelectionCriterion Area/deg2 Nobs(Ncand) Nw/z(Nobs)
K<18.4BrightSample
VHS-DESSPTa (J−K)>1.6,(W1−W2)>0.85 498 12(12,100%) 7(12,58%)
VHS-ATLASNGCa,c (J−K)>1.6,(W1−W2)>0.85,Y >J 421 5(9,56%) 3(5,60%)
VHS-ATLASSGCa (J−K)>1.6,(W1−W2)>0.85,Y >J 488 1(1,100%) 0(1,0%)
VHS-DESS82-Wa,b (J−K)>1.6,(W1−W2)>0.85 129 5(5,100%) 1(5,20%)
i>20.5,(i−K)>2.5
UKIDSS-LASS82-Eb (J−K)>1.6,(W1−W2)>0.85 116 5(7,71%) 5(5,100%)
i>20.5,(i−K)>2.5
UKIDSS-LASDR10a,b (J−K)>1.6,(W1−W2)>0.85,(H−K)>1.4 3131 6(5,83%) 3(5,60%)
18.4<K<18.9IntermediateSample
VHS-DESSPTa (J−K)>1.6,(W1−W2)>0.85 498 17(17,100%) 9(17,53%)
VHS-DESS82-Wa,b (J−K)>1.6,(W1−W2)>0.85 129 4(4,100%) 2(4,50%)
i>20.5,(i−K)>2.5
VHS-ATLASSGCa (J−K)>1.6,(W1−W2)>0.85,Y >J 488 2(2,100%) 2(2,100%)
18.9<K<19.3FaintSample
VHS-DESSPTDeepa (J−K)>1.6,(W1−W2)>0.85 83 4(4,100%) 1(4,25%)
aThisWorkbBanerjietal.2012cBanerjietal.2013
2.2 OpticallyBrightReddenedQuasarCandidateswith The quasar candidates were expected to cover a broad range in
SDSSSpectroscopy redshift, similar to the samples in B12 & B13, and use of the
SINFONI H +K filters was therefore requested. However, due
BeforedescribingourNIRspectroscopicobservations,weexamine
totechnicaldifficulties,onlytheSINFONIR=4000K-bandgrat-
theSDSS/BOSSopticalspectrafortheoptically-brightobjectsin
ing was available. The K-filter has a wavelength range of 1.9-
theVHS-DESStripe82.Therearefivereddenedquasarcandidates,
2.5µm, corresponding to a redshift range of 2.1<z<2.7 for Hα
based on their (J − K) and (W1− W2) colours, which have
andredshifts3.1<z<4.1forHβ and[OIII]λλ4959,5007. Atred-
i<20.5and/or(i−K) <2.5andwerethereforeremovedfrom
shifts0.5<z <2.1however,nostrongemissionlinesarevisible
ourfinalcandidatelist.SpectraforthesesourcesareshowninFig.
in the K-band so this represents a redshift desert for our survey.
1.Threeobjectsareatz < 0.6;twoappeartobemorphologically
ULASJ2219+0036(seeSection2.2)isanexampleofacandidate
compactstar-forminggalaxieswhileoneisalow-redshiftquasar.
intheredshiftdesert.
The two remaining optically bright candidates with SDSS
The dispersion is 2.5A˚ per pixel. Observations were carried
spectra are both quasars at higher redshifts. ULASJ2219+0036
outinnoAOmode,utilisingthelargestfieldofviewoftheinstru-
(SDSS J221930.42+003626.3), a quasar at z = 1.196, was also
ment,whichis8×8arcsec.Thetargetswereoffsetby±1.5arcsec
identifiedinB12,whereNIRspectroscopywaspresented.Noemis-
inRAandDECfromthecentreoftheIFUforsky-subtractionpur-
sion lines were detected, confirming that our NIR spectroscopy
poses. Apart from the choice of filter, the observational setup is
can fail to identify reddened quasars at low redshifts. SDSS
identicaltothatinB12.Thetotalintegrationtimewasadjustedde-
J220325.00-004002.8, a quasar at z = 2.565, possesses a spec-
pendingontheK-bandmagnitudeofeachsourceandtheprevail-
trumwithablueUVcontinuumandisthereforenotaheavilydust-
ingconditionsatthetimeofobservation.Faintertargetstherefore
reddenedquasar.Wenotethatboththesehighredshiftquasarshave
havemuchlongerexposuretimes,chosensuchthatanybroad-lines
spectroscopy fromtheBOSSsurveybutnotfromtheSDSSData
presentshouldbedetectedathighS/Ninthebinnedspectra.
Release7.
All data were reduced using standard ESO pipeline recipes
As demonstrated in Rossetal. (2014), red quasars selected
using the gasgano data reduction package. Data reduction steps
from the SDSS/BOSS surveys constitute a heterogenous popula-
included dark subtraction, non-linearity corrections, flat-fielding,
tionincludingreddenedType1quasars,Type2quasars,BroadAb-
sky subtraction, extraction and wavelength calibration. Relative
sorption Line quasars, as well as sources with extreme emission
flux calibration was performed using telluric standards observed
lineequivalent widths.Eachofthesepopulations isinterestingin
atsimilarairmasstothetarget.Typically,fourtofivetelluricstan-
itsownrightbutinthiswork,wearespecificallyinterestedinin-
dardswereobservedthroughthenight.Duetotheabsenceofspec-
vestigatingthepropertiesofthereddenedType1quasarsandour
trophotometricstandardsintheNIR,absolutefluxcalibrationwas
targetselectionisdesignedtoisolatethissubsetofredobjects.
achievedbynormalisingthespectrausingtheK-bandmagnitudes
ofthetargets.
From our final list of 53 spectroscopic targets, 48 objects
were successfully observed with SINFONI over the three nights.
3 SPECTROSCOPICFOLLOW-UP
Twenty-fourshowbroad-linesintheNIRK-bandspectrumandare
Follow-upof our reddened quasar spectroscopic targetswas con- thereforespectroscopicallyconfirmedtobequasars,withredshifts
ductedinVisitorModeoverthreefullnightsin2013Julyusingthe assigned assumingthat theemissionlineisHα. Wenotethat the
SINFONI spectrograph on the Very Large Telescope (VLT). The observedequivalentwidthsoftheselinesareinconsistentwithcor-
seeingrangedfrom0.5to1.0arcsecwithamedianof0.78arcsec. respondingtootherBalmerlines(e.g.Paα,Paβ)atlowerredshifts,
(cid:13)c 0000RAS,MNRAS000,000–000
HeavilyReddenedType 1Quasarsatz > 2 5
SDSSJ220325.00-004002.8 SDSSJ210050.13-005752.5
z=2.565 BOSS QSO z=0.25 BOSS Faint QSO Target
30 12
25 αLy NV 10 [OII] αH
−1A 20 CIV HeII CIII] −1A 8
−2m −2m
−1g s c 15 −1g s c 6
−170 er 10 −170 er 4
1 1
F/λ 5 F/λ
2
0
0
−5
1200 1400 1600 1800 2000 2200 2400 3000 3500 4000 4500 5000 5500 6000 6500 7000
Rest−Wavelength/A Rest−Wavelength/A
SDSSJ204837.25-002437.2 SDSSJ205601.68-001613.3
z=0.433 BOSS Faint QSO Target z=0.521 BOSS QSO
10 100
9 90
8 [OII] OIII] 80 MgII γH βH
−1A 7 [ −1A 70
−2m 6 −2m 60
−1erg s c 45 −1erg s c 50
−170 3 −170 40
1 1
F/λ 2 F/λ 30
1 20
0 10
−1 0
3000 3500 4000 4500 5000 5500 6000 2500 3000 3500 4000 4500 5000 5500 6000
Rest−Wavelength/A Rest−Wavelength/A
SDSSJ221930.42+003626.3
z=1.196 BOSS QSO
14 CIII] MgII
12 OII]
[
−1A 10
−1−2erg s cm 68
−170 4
1
F/λ
2
0
−2
2000 2500 3000 3500 4000
Rest−Wavelength/A
Figure1.SDSSspectraofopticallybrightreddenedquasarcandidates(blacksolid)alongwiththebestmodel-fitusedfortheredshiftdeterminations(dashed
red).Note,allofthesewerequasartargetswithinBOSS.
which are expected to be at least an order of magnitude weaker 4 DEMOGRAPHICSOFTHEREDDENEDQUASAR
(Glikmanetal.2006).Thespectroscopicallyconfirmedquasarsto- POPULATION
gether with their coordinates, K-band magnitudes, redshifts and
exposuretimesarelistedinTable2.Onedimensionalspectra,ex-
4.1 SpectralEnergyDistributions,DustExtinctions&
tractedoverregionsmaximisingtheS/NoftheHαemissionline, BolometricLuminosities
arepresentedforallobjectsinFig.A1.
To provide estimates of dust extinctions and luminosities we fit
themulti-wavelengthphotometricdataforourconfirmedreddened
(cid:13)c 0000RAS,MNRAS000,000–000
6 M. Banerjiet al.
Table2.SummaryofSpectroscopicallyConfirmedReddenedQuasars.
Name RA DEC K Redshift Exposuretime(s)
AB
VHS-DESSPTRegion
VHSJ2024-5623 306.1074 −56.3898 18.76 2.282 1800
VHSJ2028-4631 307.0083 −46.5325 18.87 2.464 1800
VHSJ2028-5740 307.2092 −57.6681 17.25 2.121 800
VHSJ2048-4644 312.0435 −46.7387 18.78 2.182 1600
VHSJ2100-5820 315.1403 −58.3354 18.47 2.360 1600
VHSJ2101-5943 315.3311 −59.7291 16.68 2.313 320
VHSJ2115-5913 318.8818 −59.2188 17.63 2.115 800
VHSJ2130-4930 322.7490 −49.5032 18.47 2.448 1600
VHSJ2141-4816 325.3530 −48.2830 18.54 2.655 1600
VHSJ2212-4624 333.0796 −46.4101 18.72 2.141 1800
VHSJ2220-5618 335.1398 −56.3107 16.72 2.220 320
VHSJ2227-5203 336.9491 −52.0582 18.80 2.656 2200
VHSJ2235-5750 338.9331 −57.8372 17.95 2.246 1000
VHSJ2256-4800 344.1444 −48.0088 17.80 2.250 1000
VHSJ2257-4700 344.2589 −47.0157 18.51 2.156 1600
VHSJ2306-5447 346.5011 −54.7881 18.17 2.372 1000
VHSJ2332-5240 353.0387 −52.6780 19.16 2.450 2400
VHS-ATLASSGCandNGCRegions
VHSJ1556-0835 239.1571 −8.5952 18.20 2.188 1200
VHSJ2143-0643 325.8926 −6.7206 18.48 2.383 1600
VHSJ2144-0523 326.2394 −5.3881 18.71 2.152 1600
VHS-DESStripe82Region
VHSJ2109-0026 317.3630 −0.4497 18.59 2.344 1600
VHSJ2355-0011 358.9394 −0.1893 18.42 2.531 1600
UKIDSS-LASDR10(H−K)>1.4
ULASJ0123+1525 20.8022 +15.4230 18.59 2.629 1200
ULASJ2315+0143 348.9843 +1.7307 18.38 2.560 400
quasars using the quasar SED models of Maddoxetal. (2008, Thereare,however,afewexamplesofreddenedquasarswith
2012).IntheVHS-DESSPTregionthedataconsistsofphotometry Hα equivalent widths of up to ≃500A˚. For comparison, the K-
inJHK andWISEW1andW2.FortheStripe82,VHS-ATLAS band filterintheVISTAsurvey hasaneffective widthof 3090A˚
andUKIDSSregions,opticalphotometry(fromtheStripe82coadd or 940A˚ in the rest-frame at z=2.3. When deriving E(B −V)-
surveyandSDSS)isalsoavailableandhasbeenutilisedintheSED estimates,itisimportantthatweaccount fortheeffectoftheHα
fitting.ThefittingprocedureisdescribedinB12andaccountsfor lineon thecontinuum K-band flux.Wetherefore proceed asfol-
the effect of the observed Hα equivalent width on the (J −K) lows.TheHαlineintheSEDmodelisscaledtohavethesamerest-
coloursasfollows.Theequivalent widthoftheHαemissionline frameequivalentwidthpresentineachindividualreddenedquasar.
inourbaseSEDmodelhasbeenderivedbyfittingtotheobserved AsisevidentfromTableA1thescaling-factorisclosetounityfor
colours(ugrizYJHK)ofluminous,unobscured,quasarsinSDSS themajorityofquasars.TheE(B−V)valuesarethenderivedby
DR7 that possess SDSS and UKIDSS photometry. The quasar fittingthescaledSEDtoalltheobservedphotometryavailablefor
SED model (Maddox et al. 2012) takes into account luminosity- each quasar. In this way, the specific contribution to the K-band
dependentchangesintheHαequivalentwidthduetotheBaldwin fluxbytheHαemissionlineineachquasar istakenintoaccount
effect (Baldwin 1977). The base quasar-SED model has already andtheE(B−V)estimatesareindependentoftheemission-line
beenshowntoprovideaverygoodmatchtotheobservedcolours strength.
ofluminousSDSSDR7quasarsovertheredshiftrange0.2<z<4.0 Ourmodelalsoincludesaluminositydependentcontribution
(Maddox et al. 2012). The default rest-frame equivalent widthof fromahostgalaxy.Evenallowingfortheeffectsofextinctionon
theHαlineinourz=2.3modelis≃250A˚. the quasar SED, at the redshifts and K-band magnitudes of our
Foreachofourreddenedquasars,weestimatetherest-frame sample, the NIR-colours of the majority of the objects are domi-
Hα equivalent widths directly from the spectra. All equivalent natedbythequasarSED.Recallthatakeyelementinthesample
widthsarecalculatedbyintegratingthelinewithin±3σ,whereσ selectionisthatthecandidatesmustbeunresolvedintheK-band
isderivedfromasingleGaussianfittothelineprofile.Thecontin- and,byselection,thehost-galaxycontributioncannotbelarge.The
uumisdefinedbeyondthis3σregionoutto±10000km/sfromthe formofthehost-galaxySEDandexactcontributiontotheobserved
Hαlinecentroid.Theexactdetailsoftheequivalentwidthcalcula- NIR-coloursarethusnotsignificantinthecontextofreproducing
tionsarenotimportantasmeasurementsarearemadeconsistently theJHKW1W2photometry.
forboththeSEDmodelandtheobservedspectra.Therest-frame The strongest constraints on the reddening for each quasar
Hαequivalentwidthsforeachofourreddenedquasarsaregivenin predominantly come from the J −K colour, which probes rest-
TableA1andthemedianvalueis≃270A˚,whichisconsistentwith frame wavelengths of ∼3400-6400A˚, below the inflexion in the
thevaluefortheunobscuredquasarpopulation.Thereistherefore quasarSEDsat≃10000A˚ andabovetheUV-portionofthespec-
noevidencethatthereddenedquasarshaveunusualHαequivalent trumwheredifferentextinctioncurvesexhibitquitedifferentforms.
widthsrelativetotheirunobscuredcounterparts. ThederivedvaluesofE(B−V)arethuscompletelyinsensitiveto
(cid:13)c 0000RAS,MNRAS000,000–000
HeavilyReddenedType 1Quasarsatz > 2 7
whichextinctioncurve(e.g.curvesappropriatefortheMilkyWay, where L is estimated using the best-fit model SEDs of each
5100
Large or Small Magellanic Clouds) is incorporated in the model quasar. The Hα rest-frame full-width-half-maximum (FWHM) is
fits.Giventhephotometricuncertainties,theestimatesofE(B−V) calculatedfromeitherasingle-oradouble-Gaussianfittotheline
areaccurateto≃ ±0.1 mag.Extinctionvaluesaresummarisedin profile in the velocity range ±10000kms−1. Double Gaussians
Table3andthemedianE(B−V)isfoundtobe0.8mag,consistent are only used if they produce a statistically significant improve-
withthevaluesreportedinB12andB13. menttotheline-profilefitcorrespondingtoalowermean-fiterror.
AsdemonstratedinBanerjietal.(2014),thesedustextinction AllGaussiancomponentsareconstrainedtopossessFWHMinthe
estimates derived from SED-fittingto the broadband photometry, range 1000-10000kms−1, ensuring they trace broad-line region
areinexcellentagreementwiththosefromindependentX-rayob- gas.Errorsontheblack-holemassesarederivedbypropagatingthe
servations,evenforthereddestandthereforedustiestquasars.The meanfiterrorontheFWHMmeasurements. Contributionstothe
observedquasarSEDsarede-reddenedusingtheE(B−V)values, Hαemission-lineprofilefromanynarrowcomponent present are
assuminganSMC-likeextinctionlaw(Pei1992),andtheopticallu- smallandweverifiedthatincludingsuchanarrowGaussiancom-
minosityatrest-frame5100A˚ iscalculated1.Theobservedandde- ponentdidnotaltersignificantlytheFWHMofthebroadsingle-or
reddenedi-bandquasarmagnitudes,togetherwiththede-reddened double-Gaussian components. Parametrization of any narrow Hα
i-band absolute magnitudes and bolometric luminosities are pre- components, which could potentially be tracing star formation in
sentedinTable3.Note,thesei-bandabsolutemagnitudes arere- thequasar host galaxy, isdiscussed inAlaghband-Zadeh et al(in
latedtotheSDSSM magnitudesviaM =M +0.596. preparation).
i[z=2] i i[z=2]
Thetotalluminositiesareestimatedusingabolometriccorrection The Gaussian line fits are included in Figure A2, while the
factorof7appliedtotherest-frame5100A˚ luminosity(Netzeretal. FWHMvaluesandderivedblack-holemassesaretabulatedinTable
2007)2. A1andTable3respectively.
4.2 Black-HoleMasses 4.3 ComparisontoUnobscuredQuasarsfromSDSS
Single-epochquasarblack-holemassesarenormallyderivedbased The black-hole masses and bolometric luminosities can be used
onavirialestimator,employingthewidthsofbroademissionlines to derive Eddington ratios (L/L ) which are typically >0.1,
Edd
and assuming acalibration between thesizeof thebroad-line re- as was found in B12 and B13. The reddened quasars therefore
gionandthequasarluminosity.Thecalibrationhasbeenderivedus- appear to be massive black holes, accreting at a high rate, re-
ingreverberationmappingtechniquesatlowredshift(Kaspietal. sulting in their very high luminosities. Large numbers of unob-
2000, 2005) and for relatively low-luminosity AGN; the validity scured, luminous and highly accreting black-holes are known,
ofextrapolatingthetrendstohighredshiftandhigherluminosities, e.g.from SDSS (Schneideretal. 2007) and BOSS (Paˆrisetal.
stillremainsuncertain.Inaddition,virialblack-holemassestimates 2014), and the luminosity function and space density of the
canbesensitivetothechoiceofbroadlineused,andthedetailsof obscured and unobscured populations are of potential interest.
theline-fitting. A further complication can result ifthere aresig- We define a sample of 2081 ‘unobscured’ quasars from SDSS
nificantinflowsandoutflowsaffectingthegasclosetotheaccret- DR7, with redshifts 2.1< z <2.7 and magnitudes K <18.9
ingblack-holethatcanartificiallybroadentheobservedlinewidths. as well as black-hole mass and bolometric luminosity estimates
IfreddenedquasarsdocorrespondtotheAGN-feedbackphasein from Shenetal. (2011). The combined sample of spectroscopi-
galaxy formation, such inflows and outflows would be more pre- cally confirmed reddened quasars from B12, B13 and this paper,
dominantinoursampleandindeedseveraloftheHαlineprofiles over the same redshift range and brighter than K <18.9 repre-
shown in Figure A2 clearly show evidence for very broad wings sentsthe‘reddened’-quasar population. Thedistributionofblack-
thatcouldresultfromsuchflows. hole masses and luminosities for the two samples are shown in
Despite these caveats, single-epoch black-hole masses are Fig. 2. The mean black-hole masses and bolometric luminosities
still widely used and there is general consistency between mass arelog10(MBH/M⊙)=9.7±0.4,log10(Lbol/ergs−1)=47.1±0.4and
estimates obtained from different broad-lines (Shenetal. 2011; log10(MBH/M⊙)=9.3±1.1, log10(Lbol/ergs−1)=47.0±0.2 for the
Matsuokaetal. 2013). Wetherefore provide such mass estimates reddenedandunobscuredsamplesrespectively.
forourreddenedquasarsample.Specifically,weemploythemass The distributionsof black-hole mass and luminosity overlap
estimator of Vestergaard&Peterson (2006), using the calibration significantly (Fig. 2), but there is an indication that the reddened
betweenHαandHβlinewidthsfromGreene&Ho(2005): quasars possess a tail out to higher bolometric luminosities and
black-holemasses.Severalselectioneffectsandsystematicerrors
FWHM 1.03±0.03 couldberesponsibleforthisobservedtail.Theblackholemasses,
FWHMHβ =(1.07±0.07)×103(cid:18)103kms−Hα1(cid:19) kms−1 derived from UV-emission lines for objects in SDSS and Hα for
the reddened population, may not be on exactly the same scale.
(1)
Progress is being made via direct comparison of emission-line
propertiesinquasarsamples(Matsuokaetal.2013;Tilton&Shull
MBH/M⊙ =106.91(cid:18)1F0W00HkmMsH−β1(cid:19)2(cid:18)104L45e1r0g0s−1(cid:19)0.5 (2) 2d0iv1i3d)uabluetmthisesiuonncleirnteasinrteymianinbslascikgnhifiocleanmta(es.sg.esSthimenateetsafl.ro2m01i1n)-.
Moreimportantly,inflowsandoutflowsarelikelytobemorecom-
moninthereddenedpopulation,thoughttobecaughtintheAGN
1 Aswiththedetermination ofthe E(B−V)-values, thederived opti-
radiative feedback phase. The presence of such flows could add
cal luminosities areinsensitive towhich conventional extinction curve is
significantadditionalspreadtotheobservedlinewidths,increasing
employed.
2 Abolometriccorrection factorofcloserto9hasalsobeenusedinthe black-holemassesbyfactorsofafew(B12).Theblack-holemasses
literature (Shenetal.2011)andwouldincrease ourestimated bolometric shouldthereforebeinterpretedwithcaution.
luminositiesby∼0.1dex. The bolometric luminosities of the samples may also differ
(cid:13)c 0000RAS,MNRAS000,000–000
8 M. Banerjiet al.
0.35 0.25
SDSS SDSS
0.3 Red Quasars Red Quasars
0.2
Counts0.02.52 Counts0.15
d d
e e
s s
mali0.15 mali 0.1
Nor 0.1 Nor
0.05
0.05
0 0
45 45.5 46 46.5 47 47.5 48 48.5 49 8 8.5 9 9.5 10 10.5 11
log (L /erg s−1) log (M /M)
10 bol 10 BH 0
Figure2.Distributionofbolometricluminosity(left)andblack-holemass(right)fortheredandunobscuredquasarpopulations (seedescriptions inSec-
tion4.3).Thereissignificantoverlapbetweenthesamplesinbothluminosityandmass,althoughthereisasuggestionthattheredpopulationincludesatailof
quasarswithveryhighbolometricluminositiesandblack-holemasses.
systematically.Luminositiesfortheunobscuredquasarsampleare Wrightetal.(2010).Justafewofthereddestsourcesextendinto
calculatedusingthe1350A˚ rest-frameluminosityandassumeadif- theObscuredAGNlocus.
ferentmodelquasarSEDtoours.Mostlikely,however,isaselec- Fig.3suggeststhat,crudely,thereddenedquasarsareindistin-
tionagainstthemostluminousquasarsintheSDSSresultingfrom guishablefromunobscuredquasarsintermsoftheirWISEcolours.
thebrighti-bandflux-limitof15.0mag(c.f.thevaluesforthered- We can test this quantitatively by fitting a power-law to the ob-
denedquasarsinCol.4ofTable3). served WISE fluxes in the W1, W2 and W3 bands of the form
Overall, notwithstanding the caveats summarised above, we λF ∝λβNIR.Emissionfromhotdustisexpectedtodominatethe
λ
canconcludethatthereddenedquasarsampleconsistsofapopula- SEDsoverthe1–4µmrest-framewavelengthrangeprobedbythe
tionofveryhighmassblack-holes,comparabletothemostmassive WISEpassbands.Wefindameanvalueofβ =0.69inoursam-
NIR
black-holesincludedintheSDSSquasarsample. ple4 withastandarddeviationof0.29.ThemeanNIRpower-law
indexfortheSDSSsampleis0.50±0.26,consistentwiththeresults
fromWangetal.(2013)andHaoetal.(2011).
The SDSS and reddened-quasar power-law indices agree
5 INFRAREDSEDSFROMWISE within1σ ofthepopulation deviationandthesteepermeanvalue
for the reddened quasars is consistent with the most obscured of
Comparingthemulti-wavelengthpropertiesofthereddenedquasar
ourquasarsshowingsomeextinctionatrest-framewavelengthsof
sampletootherwell-studiedgalaxyandAGNpopulationsatsimi-
1–2µm,whichsteepenstheslopeoftheSED.Fig.4showsthedis-
larredshifts helpsinunderstanding theoriginof thesample. The
tributionofβforbothpopulations.Thehighβ tailisduetothe
availability of the WISE photometry, probing rest-frame wave- NIR
reddestquasarsinoursample,withE(B−V)&0.8,asexpected.
lengthsoutto&3µmforobjectsdetectedintheW3-band,provides
Several recent studies have focused on the subset of high
informationforakeyportionofquasarSEDs.Anunobscuredcom-
redshift AGN that are extremely bright in the W4 22µm band.
parisonsampleisdefinedbyselecting1604SDSSDR7andDR10
Rossetal. (2014) studied a sample of SDSS and BOSS spectro-
quasarswith2.1 < z < 2.7,K < 18.9anddetectionsinthe
AB scopically confirmedquasars withW4 <= 8magand theWISE
WISEW123-bands-hereafterthe‘SDSSsample’.
consortium have selected hyperluminous infrared galaxies, with
The reddened quasar sample was selected using a (W1 −
W4.7.7mag,thatareextremelyredintheir(W1−W2)colours
W2)> 0.85colourcutasdetailedinSection2andaretherefore,
(Eisenhardtetal.2012;Wuetal.2012).Ourselectionforreddened
by definition, red in the bluer WISE bands3 We show the WISE
quasarsdoesnotusethe22µmfluxes,although, byselectingob-
coloursofourspectroscopicallyconfirmedquasarsinFig.3onthe
jectsthatarebrightintheK-band,wearebydefinitionnotsensi-
colour-colourlocusintroducedbyWrightetal.(2010).Alltheob-
tivetotheWISE‘W12’drop-outs.Twenty-fiveofour38reddened
jectsaredetectedat>3σintheW312µmbandandthemajority
quasars aredetectedat > 3σ inthe W4band. Ofthese, 14 have
haveW1W2W3-coloursplacingthemintheQSO/Seyfertlocusof
W4<=8magand11haveW4<=7.7mag,37and29percent
ofthesamplerespectively.The22µm-detectedobjectsaregener-
ally the most bolometrically luminous quasars in our sample, as
3 AllWISEphotometrypresentedinthissectionaretakenfromthenew, expected.
improvedWISEdatareductionsavailablethroughtheAllWISEdatarelease.
For objects detected in the WISE W4-band, rest-frame lu-
However, theWISE mainsurveycatalogue wasusedforthetarget selec-
minosities at 6µm can be estimated using the W3 and W4
tionastheAllWISEreductionswerenotavailableatthetime.Wefindthat
theWISEandAllWISEfluxesaregenerallyconsistentapartfromasingle
quasar:VHSJ2024-5623. Thequasarsatisfiedthe(W1−W2) > 0.85
colour cut in the original WISE data release with W1 = 16.52 and 4 Theconvention for βNIR employed here is in wavelength rather than
W2 = 15.49buthas revised magnitudes inAllWISE ofW1 = 16.17 frequencyspacecomparedtoourpreviouswork(B13).Thetwoslopesare
andW2=15.44. relatedbyβNIR=βNIR(B13)+1.
(cid:13)c 0000RAS,MNRAS000,000–000
HeavilyReddenedType 1Quasarsatz > 2 9
Table3.Best-fitdustextinction,reddenedandde-reddenedopticali-bandmagnitudes,absolutei-bandmagnitudes,bolometricluminosities,black-holemasses
andEddingtonratiosofthereddenedquasars.
Name E(B-V) irAeBd idAeBred Mi log10(Lbol/ergs−1) log10(MBH/M⊙) lEdd dm/dt(M⊙yr−1)
VHS-DESSPTRegion
VHSJ2024-5623 0.6 22.9 17.8 −27.37 46.7 9.8±0.1 0.06 9
VHSJ2028-4631 0.6 22.9 17.9 −27.49 46.7 9.2±0.2 0.2 9
VHSJ2028-5740 1.2 24.3 14.6 −30.18 47.9 10.1±0.1 0.4 127
VHSJ2048-4644 0.7 23.2 17.4 −27.65 46.8 9.2±0.1 0.3 11
VHSJ2100-5820 0.8 23.6 16.5 −28.49 47.1 9.1±0.1 0.8 24
VHSJ2101-5943 0.8 21.8 14.9 −30.03 47.8 10.5±0.1 0.1 106
VHSJ2115-5913 1.0 23.5 15.4 −29.48 47.5 9.3±0.1 1.4 61
VHSJ2130-4930 0.9 24.7 16.5 −28.75 47.2 9.5±0.2 0.4 31
VHSJ2141-4816 0.8 23.8 16.1 −29.10 47.3 9.6±0.2 0.4 40
VHSJ2212-4624 0.8 23.7 17.2 −27.64 46.9 9.9±0.1 0.07 14
VHSJ2220-5618 0.8 21.6 14.9 −30.09 47.8 9.9±0.1 0.5 106
VHSJ2227-5203 0.9 25.0 16.3 −29.15 47.4 10.0±0.1 0.2 41
VHSJ2235-5750 0.6 21.9 16.9 −28.28 47.1 10.1±0.1 0.07 20
VHSJ2256-4800 0.6 21.7 16.7 −28.49 47.1 10.1±0.1 0.08 24
VHSJ2257-4700 0.7 23.0 17.3 −27.67 46.9 9.5±0.1 0.2 13
VHSJ2306-5447 0.7 23.2 17.1 −28.15 47.0 10.0±0.1 0.08 18
VHSJ2332-5240 0.6 23.4 18.0 −27.39 46.7 9.5±0.1 0.1 8
VHS-ATLSGCandNGCRegions
VHSJ1556-0835 0.7 22.7 16.9 −28.15 47.0 8.6±0.1 1.9 19
VHSJ2143-0643 0.8 23.8 16.7 −28.33 47.1 10.0±0.1 0.09 22
VHSJ2144-0523 0.6 22.6 17.7 −27.33 46.7 9.9±0.1 0.04 9
VHS-DESStripe82Region
VHSJ2109-0026 0.7 23.3 17.2 −27.95 46.9 9.8±0.1 0.1 15
VHSJ2355-0011 0.7 23.2 16.6 −28.67 47.2 10.1±0.1 0.09 27
UKIDSS-LASDR10(H−K)>1.4
ULASJ0123+1525 1.3 27.7 15.4 −30.12 47.8 9.7±0.2 0.9 114
ULASJ2315+0143 1.1 26.2 16.1 −29.43 47.5 10.1±0.2 0.2 57
Table4.WISEW3andW4magnitudesforallreddenedquasarsdetectedat>3σat22µmalongwiththerest-frame6µmluminosity.
Name W3(mags) W4(mags) log10(L6µm/ergs−1)
ULASJ0123+1525 8.69±0.03 6.33±0.06 47.8
ULASJ0144-0114 10.07±0.05 8.02±0.21 47.1
ULASJ0221-0019 10.46±0.06 8.11±0.17 46.9
ULASJ1234+0907 9.17±0.04 7.28±0.17 47.4
VHSJ1350-0503 10.62±0.07 8.59±0.26 46.7
VHSJ1409-0830 10.33±0.06 8.31±0.23 46.9
ULASJ1455+1230 10.43±0.05 8.11±0.15 46.3
ULASJ1539+0557 9.10±0.03 6.56±0.06 47.8
VHSJ2028-5740 9.15±0.03 7.01±0.08 47.3
VHSJ2048-4644 10.42±0.08 7.92±0.18 46.9
VHSJ2100-5820 10.70±0.10 8.14±0.24 46.9
VHSJ2101-5943 9.25±0.03 6.84±0.07 47.4
VHSJ2115-5913 9.48±0.04 7.06±0.08 47.2
VHSJ2130-4930 10.69±0.09 8.52±0.33 46.9
VHSJ2141-4816 10.46±0.07 7.68±0.16 47.3
ULASJ2200+0056 10.23±0.06 7.80±0.17 47.2
VHSJ2212-4624 11.02±0.12 8.37±0.27 46.7
VHSJ2220-5618 8.77±0.03 6.37±0.05 47.6
VHSJ2227-5203 10.11±0.06 8.02±0.22 47.2
VHSJ2235-5750 9.97±0.05 7.84±0.17 47.0
VHSJ2256-4800 9.67±0.04 7.52±0.13 47.1
VHSJ2257-4700 10.77±0.09 8.43±0.28 46.7
ULASJ2315+0143 9.57±0.04 7.03±0.10 47.5
VHSJ2332-5240 11.51±0.20 8.45±0.31 46.9
VHSJ2355-0011 9.83±0.05 7.40±0.14 47.3
(cid:13)c 0000RAS,MNRAS000,000–000
10 M. Banerjietal.
4 0.25
SDSS DR7+DR10
3.5 Red Quasars
0.2
3
s
2 (Vega) 2.25 ed Count0.15
W1−W 1.15 ormalis 0.1
N
0.5
0.05
0
−0.5 0
−1 0 1 2 3 4 5 6 7 −0.5 0 0.5 1 1.5
β
W2−W3 (Vega) NIR
Figure3.LocationofreddenedquasarsinWISEcolour-colourplanetaken Figure4.DistributionofNIRpower-lawindices,βNIR,fitintherest-frame
fromWrightetal.(2010)showingthattheyoverlaptheQSO/Seyfertlocus. wavelengthrange1-4µmbothforourreddenedquasarsampleandSDSS
unobscuredquasarsoverthesameredshiftrangeanddowntothesameK-
bandfluxlimit.
48.2
SDSS DR7+DR10 Cloverleaf
photometry. At the median redshift of z =2.3 for our sample, 48 Red Quasars
the W3 band corresponds to 3.6µm and the W4 band corre- 47.8 WISE HyLIRGs
esparonidnstetropo6la.7tiµonm,.uTsihneg6thµemrelustm-firnaomsietiewsaavreelecnagltchuslacteodrrevsipaolnidn-- −1g s) 47.6
ing to the W3 and W4 magnitudes, and the results are given in / erm47.4
SlTuaDmbSlienSo4sDitaRyn7di+sDillolRug1s1t00ra(Ltsea6dmµmpinl/eeFrgoigfs.−1513.)3=T64h7e2.1.1a±v<0er.4ag.zeFor<ersat-2fcr.oa7mmqepua6arasµbamrles og(Lµ106 474.72
l
with K< 18.9 and >3σ detections in the W4 band, the av- 46.8
erage luminosity is log (L /erg s−1)=46.8±0.2. There are
10 6µm 46.6
six SDSS quasars with log (L /erg s−1)> 47.5 (four from
10 6µm
SDSS DR7 and two from SDSS DR10). The brightest of these 46.4
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7
six is the well-known gravitationally-lensed Cloverleaf quasar Redshift
(Magainetal.1988).SDSSJ000610.67+121501.2(z=2.309)and
Figure 5. Redshift versus rest-frame 6µm luminosity for our reddened
SDSSJ155102.79+084401.1 (z = 2.520), thetwo DR10objects,
quasars compared to unobscured quasars from SDSS as well as 3WISE
werepresentedintheextremelyredsamplestudiesbyRossetal.
HyLIRGsfromSternetal.(2014).Thebrightestunobscuredquasaronthis
(2014).Bycomparison, our reddenedquasar sample,selectedus-
plotisthelensedCloverleafquasar.
ing imaging data covering less than a third of the total SDSS
imagingarea(∼14,555deg2 fromPaˆrisetal.2014),includesfour
quasars with log (L /erg s−1)> 47.5, highlighting the in-
10 6µm
6 OBSCUREDBLACK-HOLEGROWTHATTHE
creasedprevelanceofsuchluminousquasarsamongtheobscured
HIGHESTQUASARLUMINOSITIES
sample.ComparedtoWISE-selectedHyLIRGswherethemostlu-
minousobjectat6µm,WISEJ1814+3412(Eisenhardtetal.2012), Witha sample of 38 reddened quasars (E(B−V) >= 0.5), of
haslog10(L6µm/ergs−1)=47.30±0.05(Sternetal.2014),thered- which36lieatz > 2,nowinplace,adirectcomparisonoftheir
denedquasar sampleisalsoextreme,withsevenobjectsmorelu- spacedensitytothatofunobscuredquasarscanbemade.Asdeep
minousthanWISEJ1814+3412. X-ray and mid-infrared surveys have focussed on studying much
Finally,wecomparethe6µmluminositiestothebolometric fainter,dusty,AGN,thesampleallowsustoaddressthekeyques-
luminosities in Table 3, and find a typical bolometric correction tionofhowmanyveryluminousquasarsaredust-obscuredatred-
factorof∼2,consistentwithamodelinwhichalargefractionof shiftsz ∼ 2−3.Webeginbyconsideringtheselectionfunction
thetotalluminosityisre-radiatedatmidinfraredwavelengths.This andcompletenessofourreddenedquasarsample.
bolometriccorrectionfromthemidinfraredisalsobroadlyconsis-
tentwiththatderivedforthemostluminousessentiallyunobscured
quasars in SDSS and WISE (Weedmanetal. 2012). As the 6µm 6.1 SampleCompleteness
rest-frameluminositiesareinferreddirectlyfromtheobservedpho-
6.1.1 MorphologyCut
tometrywithoutanyassumptionsregardingthedustextinctionlaw
and the form of the quasar SED, this analysis corroborates our Thesampleselection(Section2)includesarequirementthatcan-
conclusion in Section 4.1, that our reddened quasars correspond didatesareunresolvedintheK-band.Whileeliminatingcontami-
tosomeofthemostintrinsicallyluminousquasarsknown. nationbylow-redshiftquasars,wherehostgalaxiescancontribute
(cid:13)c 0000RAS,MNRAS000,000–000