The radio-loud AGN population at z ≳ 1 in the COSMOS field

32 Pages·2014·13.63 MB·English

A&A567,A76(2014) Astronomy
DOI:10.1051/0004-6361/201423906 &
©ESO2014 Astrophysics
(cid:2)
The radio-loud AGN population at z 1 in the COSMOS field
(cid:2)
I. selection and spectral energy distributions
RanieriD.Baldi1,2,3,AlessandroCapetti4,MarcoChiaberge5,6,7,andAnnalisaCelotti1,8,9
1 SISSA-ISAS,viaBonomea265,34136Trieste,Italy
e-mail:[email protected]
2 PhysicsDepartment,TheTechnion,32000Haifa,Israel
3 PhysicsDepartment,FacultyofNaturalSciences,UniversityofHaifa,31905Haifa,Israel
4 INAF−OsservatorioAstrofisicodiTorino,StradaOsservatorio20,10025PinoTorinese,Italy
5 SpaceTelescopeScienceInstitute,3700SanMartinDrive,Baltimore,MD21218,USA
6 INAF-IstitutodiRadioAstronomia,viaP.Gobetti101,40129Bologna,Italy
7 CenterforAstrophysicalSciences,JohnsHopkinsUniversity,3400N.CharlesStreetBaltimore,MD21218,USA
8 INAF-OsservatorioAstronomicodiBrera,viaE.Bianchi46,23807Merate,Italy
9 INFN-SezionediTrieste,viaValerio2,34127Trieste,Italy
Received30March2014/Accepted6May2014
ABSTRACT
Weselectasampleofradiogalaxiesathighredshifts(z(cid:2)1)intheCOSMOSfieldbycross-matchingopticalandinfrared(IR)images
withtheFIRSTradiodata.Theaimofthisstudyistoexplorethehigh-zradio-loud(RL)activegalacticnuclei(AGN)population
at much lower luminosities than the classical samples of distant radio sources, which are similar to those of the local population
ofradiogalaxies.Precisely,weextendedapreviousanalysisfocusedonlow-luminosityradiogalaxies.Thewidemultiwavelength
coverageprovidedbytheCOSMOSsurveyallowsustoderivetheirspectralenergydistributions(SEDs).Wemodelthemwithour
owndevelopedtechnique2SPDthatincludesoldandyoungstellarpopulationsanddustemission.Whenaddedtothosepreviously
selected,weobtainasampleof74RLAGN.TheSEDmodelingreturnsseveralimportantquantitiesassociatedwiththeAGNand
host properties. The resulting photometric redshifts range from z ∼ 0.7 to 3. The sample mostly includes compact radio sources
but also21FRIIssources; theradiopower distributionof thesamplecovers ∼1031.5−1034.3 ergs−1Hz−1,thusstraddling thelocal
FRI/FRIIbreak.Theinferredrangeofstellarmassofthehostsis∼1010−1011.5 M(cid:3).TheSEDsaredominatedbythecontribution
fromanoldstellarpopulationwithanageof∼1−3Gyrformostofthesources.However,UVandmid-IR(MIR)excessesareobserved
forhalfofthesample.ThedustluminositiesinferredfromtheMIRexcessesareintherange,L ∼1043−1045.5 ergs−1,whichare
dust
associatedwithtemperaturesapproximatelyof350−1200K.EstimatesoftheUVcomponentyieldvaluesof∼1041.5−1045.5 ergs−1
at 2000 Å. The UV emission is significantly correlated with both IR and radio luminosities; the former being the stronger link.
However,theoriginofUVanddustemission,whetheritisproducedbytheAGNofbystarformation,isstillunclear.Ourresults
show that this RLAGN population at high redshifts displays a wide variety of properties. Low-power radio galaxies, which are
associatedwithUV-andIR-fainthostsaregenerallysimilartoredmassivegalaxiesofthelocalFRIs.Attheoppositesideofthe
radioluminositydistribution,largeMIRandUVexcessesareobservedinobjectsconsistentwithquasar-likeAGN,asalsoprovedby
theirhighdusttemperatures,whicharemoresimilartolocalFRIIs.
Keywords.galaxies:active–galaxies:high-redshift–galaxies:jets–galaxies:nuclei–galaxies:photometry
1. Introduction fundamental issues of modern astrophysics, such as accretion
ontoblackholes(BH),theco-evolutionbetweenthehostgalaxy
The advent of a multiband dataset from large area surveys
andBH,andthefeedbackprocessoftheactivegalacticnucleus
markedthestartingpointofanewscientificapproachbasedon
(AGN)ontheinterstellarandinterclustermedium(e.g.Hopkins
large samples of sources through a multiwavelength analysis.
etal.2006;Fabianetal.2006).Inthiscontext,thecross-match
The immense number of sources and the completeness of the
of radioand opticalsurveysspecifically providesa uniquetool
sampleisfundamentalforobtainingresultswithhighstatistical
intheanalysisoftheradio-loud(RL)AGN.Itconsistsinidenti-
foundations. Clear examples are represented by large surveys,
fyingopticallylargenumbersofradiosourcestoobtainspectro-
suchasSloanDigitalSkySurvey(SDSS;Yorketal.2000)and scopic/photometricredshiftsand,finally,toinvestigatethelinks
COSMOS(Scovilleetal.2007),whichprovidewidemultiwave-
between the radio structures, as associated with the centralen-
length coverage. The association of targets at different wave-
gine, and the host galaxies. For example, Best et al. (2005a,b)
lengthshelpsustodeterminethepropertiesofthesourcesand,
selected a sampleof radio galaxiesby cross-correlatingoptical
especially,toderivetheirSEDs.
SDSS, radio NVSS (Condon et al. 1998), and FIRST (Becker
Among the most energetic phenomena in the Universe, ra-
et al. 1995) catalogs. This sample constitutes a very good rep-
dio galaxies occupy an important position in the study of the
resentationofradiogalaxiesinthelocalUniverse.Recently,the
(cid:2) AppendixAisavailableinelectronicformat adventof the COSMOS survey,which giveX-ray,UV, optical,
http://www.aanda.org infrared,andradiodataallatonce,facilitatesthecommunityto
ArticlepublishedbyEDPSciences A76,page1of32
A&A567,A76(2014)
selectalargesampleofsourcesonawiderrangeofwavelengths fainter,e.g.,Willottetal.2001forz (cid:2) 0.7)andsimilartothose
eventhenSDSSbutona2deg2areaofthesky. ofthelocalpopulationofradiogalaxies.
Since the COSMOS catalogs are available for the commu- Once the sample is selected, we study the multiwavelength
nity, several studies have already been carried out on radio properties (from radio to IR) of the high-z RL AGN popu-
sources. Schinnerer et al. (2004, 2007) selected ∼3600 radio- lation. We will address different studies of such a population
emitting galaxies (starburst and AGN) in the COSMOS field, in forthcoming papers. Precisely, in this work, we also per-
based on VLA radio maps at 1.4 GHz. Smolcˇic´ et al. (2008) form an analysis analogous to what Baldi et al. (2013; here-
explore the properties of the sub-mJy radio population, using afterB13)operatedonthesampleselectedbyC09.Baldietal.
theVLA-COSMOSdataset,byseparatingstar-forminggalaxies (2013),whichtakesadvantageofthelargemultiwavelengthcov-
fromAGN,whichreachL ∼1033ergs−1Hz−1.Theirsam- erage provided by the COSMOS survey, carefully identified
1.4GHz
ple is a mixtureof objects with z (cid:3) 1.2, where AGN dominate the correct counterparts of the selected radio sources at differ-
overstar-bustgalaxiesforL > 1031ergs−1Hz−1.Bardelli ent wavelengths to derive their genuine emission. They, thus,
1.4GHz
et al. (2010) investigate the properties and the environment of constructed their SEDs from the far-UV (FUV) to the mid-IR
radiosourcesatz<1bycombiningtheVLA-COSMOSdataset (MIR) wavelengths. The SED modeling with stellar templates
andtheredshift-surveyzCOSMOS(Lillyetal.2007).Thissam- returnedtheirphoto-zand,theirAGNandhostproperties.Their
ple includes low-luminosity radio-emitting objects (L < main results are the following. The resulting photometric red-
1.4GHz
1032 ergs−1Hz−1) associated with red massive (∼7×1010 M(cid:3)) shiftsrangefrom∼0.7to3.Theradiopowerdistributionoftheir
hostsinoverdenseregions. sample, ∼1031.5−1033.3 ergs−1Hz−1 at rest-frame 1.4 GHz, in-
The basic idea of this study is to select a sample represen- dicates that their radio power is indeed mostly consistent with
tative of the RL AGN population at z (cid:2) 1 to investigate the local FR Is. Yet, a small contribution of sources show larger
propertiesoftheradiogalaxiesinacosmicera,wheretheAGN radio power above the local FR I/FR II break1. Most of the
activityplaysafundamentalroleinthegalaxyformation.Sucha hosts of these high-zlow-luminosity radio sources are massive
samplecanbeusedtoanswerdifferentastrophysicalquestions, galaxies (∼7 × 1010 M(cid:3)) dominated by an old stellar popula-
such as the cosmologicalevolutionof radiogalaxies, the study tion(afewGyr)butsignificantexcessesineithertheUVorthe
oftheirluminosityfunction,andacomparisonwithlocalactive MIRbandareoftenpresent.
and quiescent galaxies, which are all in light of the symbiotic Inthispaper,weselectasampleofRLAGNintheCOSMOS
relation between AGN and host. For this purpose, we choose fieldwithamultiwavelengthidentificationoftheirhosts,asde-
the COSMOS field because the large multiwavelength dataset scribed in Sects. 3 and 4. Since the entire sample includes the
provided by the survey consists of a unique tool to perform a FRIcandidatesselectedbyC09andtheirpropertiesarealready
multibandselectionprocedure. studied by B13, we initially study the “newly selected” radio
The main problem of the selection of sources at high red- sourcesbyfollowingB13,andthenweconsidertheentiresam-
shiftsisrepresentedbytheobservationalbias,whichmakesflux- ple. Using the FUV-MIR data provided by the COSMOS sur-
limited samples more abundantof powerfulsources due to the vey, we derive their SED (Sect. 5), and we model them using
tight redshift-luminositydependence.In fact available samples 2SPD(2StellarPopulationandDustcomponent)techniquefor
ofRLAGNatz(cid:2)1(e.g.3CRanditsdeepersuccessors)mostly theradiosourcesselectedinthiswork.Theresultsreturnedfrom
include powerful “edge-brightened” (FR II, Fanaroff & Riley theSEDmodelingarepresentedinSect.6:thephotometricred-
1974)objects.Thisimpliesthatourknowledgeaboutthehigh-z shifts and the host properties, such as stellar ages, masses and
RLAGNpopulationmissesafundamentalpiece,whichconsists dust,andUVcomponents.InSect.7,wegathertheentiresam-
oftheweak“edge-darkened”radiogalaxies(FRI).Unlikepre- pleofdistantRLAGNintheCOSMOSfieldtostudytheirradio
viousstudiesinthiswork,wepaymuchattentiontoincludethe power distribution(Sect. 7.1) and globalproperties(Sect. 7.2).
low-power radio sources to satisfy the sample requirements of InSect.7.3,welookforrelationsbetweenradio,IR,andUVlu-
completenessandhomogeneity,asneeded.Thefirststepsinthat minosities to investigate the origin of their emission at these
direction were done by Chiaberge et al. (2009;hereafter C09). wavelengths.In Sect. 8, we summarizethe results, and we dis-
They selected the first seizable sample of FR I candidates at cussourfindings.
z (cid:2) 1 in the COSMOS field. This research is motivated by the WeadoptaHubbleconstantofH =71kms−1Mpc−1,Ω =
0 m
peculiarityofthisclassofsources.InthelocalUniverse,FRIs 0.27andΩ = 0.73,as givenbythe WMAPcosmology(e.g.
vac
typicallylive in massive early-typegalaxyin clusters. Thisbe- Spergeletal.2003;Jarosiketal.2011).Allthemagnitudesare
havior,ifsharedbytheirhigh-zcounterparts,willhelpthecom- inABmagsystem,ifnototherwisespecified.
munitytoaddressanumberofotherunsolvedproblemsincur-
rentastrophysics,suchastheevolutionoftheellipticalgalaxies,
therelationshipbetweengiantellipticalsandtheircentralBHat 2. Dataset
lownuclearluminosities,thesearchforclustertostudytheirfor-
ThephotometricdatausedtoderivetheSEDsofoursourcesare
mationandevolution,andthestudyofthepossibleFRI-quasar
takenfromtheCOSMOSsurvey(Scovilleetal.2007).Thissur-
association,notcommoninthelocalUniverse.
veycomprisesgroundbased,imaging,andspectroscopicobser-
Tostudytheoverallhigh-zRLAGNpopulation,wedeemit
vationsfromradiotoX-rayswavelengths,whichcoversa2deg2
necessarytorelaxtheselectioncriteriaandincluderadiosources
areainthesky.
regardlessoftheirmorphologyandradioflux.Inparticular,we
Optical and IR observations and data reduction are pre-
also include FR II radio sources and those with a flux higher
sentedinCapaketal.(2007,2008),andTaniguchietal.(2007).
than13mJy,whichisthehighfluxthresholdusedbyC09.This
resulting sample includes, by definition, the low-power radio
1 FR I galaxies typically have a radio power lower than that of
galaxiesselectedbyC09,despitethedifferentgoalsofselection. FR II sources with the FR I/FR II break set at L ∼ 2 ×
178MHz
Asweshowlater,theselectionprocedureyieldsasampleofra- 1033 ergs−1Hz−1 (Fanaroff & Riley 1974). The transition is rather
diosourcesofmuchlowerluminositythanclassicalsamplesof smooth and both radio morphologies are present in the population of
distantradio sources(approximatively2.5 ordersof magnitude sourcesaroundthebreak.
A76,page2of32
R.D.Baldietal.:Theradio-loudAGNpopulationatz(cid:2)1intheCOSMOSfield
A multiwavelength photometric catalog was generated using radius 5100 arcsec4 is 5155. This number also includes the ra-
SExtractor (Bertin & Arnouts 1996) and includes objects with diosourcesselectedbyC09.Giventhattheradiomorphologyis
total magnitude I < 252. The survey includes HST/ACS data fundamentaltoidentifythehostgalaxy,weonlyconsiderFIRST
(Koekemoer et al. 2007), which provides the highest angular sourceswhich have VLA-COSMOS counterpart.This strongly
resolution (∼0(cid:4).(cid:4)09) amongthe COSMOS images. Furthermore, facilitatesthehostidentificationbecauseofitshigherspatialres-
the survey gathers data from GALEX, Subaru, CFHT, UKIRT, olutionthanFIRSTimages.Intenobjects,theVLAimagedoes
NOAO,andSpitzer. not show any radio emission in correspondence of the FIRST
TheCOSMOScollaborationprovidesdifferentcatalogs.For source. These are probably diffuse objects not visible in the
VLA-COSMOSimageduetoitshigherspatialresolution.Such
this optical identification, we use the COSMOS Intermediate
andBroadBandPhotometryCatalog2008(Capaketal.2008)3 radio sources have FIRST radio flux less than 3.74 mJy (typi-
cally∼1.2mJy).
from which we take the broadband magnitudes of our sources
fromtheFUVtotheK bands.AtIRwavelengths,wealsoused Similarly to the selection procedureperformedby C09, we
theS-COSMOSIRAC4-channelPhotometryCatalogJune2007 usetheassumptionthatthepropertiesofthehostgalaxiesofthe
andS-COSMOSMIPS24PhotometryCatalogOctober2008(or RLAGNpopulationathighredshiftsaresimilartothoseofdis-
S-COSMOSMIPS24umDEEPPhotometryCatalogJune2007) tantFRIIs.TypicalFRIIradiogalaxyat1<z<2hasaK-band
tosearchfortheSpitzer/IRACandMIPScounterparts(Sanders magnitudefainterthan17(Willottetal.2003).Sincethetypical
etal.2007). I−K colorforFRIIhostisnotsmallerthan4,thisassumption
setsalowerlimitontheI-bandmagnitudeofthehostof21(in
Theselectionofthesampleisalsobasedonradiodatafrom
theSubaruorCFHTimages).Weusethisopticallimittoselect
the FIRST survey (Becker et al. 1995). The data are obtained
the optical counterparts of the FIRST radio sources. In such a
with the VLA in B configuration with an angular resolution
of∼5(cid:4)(cid:4)andreachafluxlimitof∼1mJy.Wealsouseddatafrom process, we performa roughidentificationof the I-bandcoun-
terpart.Amoredetailedhostidentificationistheaimofthenext
the NVSS survey (Condon et al. 1998) (VLA in D configura-
tion).TheNVSShasalowerspatialresolution(∼45(cid:4)(cid:4))andwith stepoftheselection.Furthermore,wealsoincluderadiosources
in the sample, which satisfy the radio selection but are either
a higher flux density limit (∼2.5 mJy) than the FIRST survey,
spectroscopicallyclassifiedasquasarorcandidatesquasarbased
butthesedataareusefulsincetheyaremoresensitivetodiffuse
on the point-like appearance in the ACS images. Such objects
low surface brightnessradio emission that the FIRST data. We
mighthaveI <21,sincetheAGNemissionoutshinesthegalaxy
alsousedatafromtheVLA-COSMOSLargeandDeepProjects
emissioninopticalband.ExcludingthesourcesoftheC09sam-
(Schinnerer et al. 2004, 2007); this is, VLA observations (in
A-Carray)oftheCOSMOSfieldataresolutionof1(cid:4).(cid:4)5andwith ple,thenewselectedobjectsintheCOSMOSfieldbasedonthe
ameanrmsnoiseof∼10μJy/beam. radioemissionandontheI-bandmagnitudeare566.
We identify the optical/infrared counterpart to the radio
TheCOSMOSsurveyalsoprovidesspectroscopicdatafrom
emissionbycheckingthemulti-wavelengthimagesofeachradio
theVeryLargeTelescope(VLT)(zCOSMOS,Lillyetal.2007)
source.DetailsofthehostidentificationareinSect.4.For46ob-
and from the Magellan (Baade) telescope (Trump et al. 2007).
jects,thisprocedureissuccessful(seeTable1),whilewedonot
In addition, the COSMOS collaboration performed their own
trustmuchinthehostidentificationfor10FIRSTradiosources
photo-zderivationmostlyforsourceswithi+ < 25.5witharel-
because of the complexityof the radio morphologyor the am-
ativeredshiftaccuracyof0.007ati+ < 22.5(Ilbertetal.2009)
biguity of the correct optical counterpart. Therefore we prefer
andalsoforopticallyidentifiedsourcesdetectedwithXMMby
to leave these ten sources out. Those sources are presented in
achieving a relative accuracy of 0.014 for i+ < 22.5 (Salvato
Table2.
et al. 2009). The COSMOS Photometric Redshift Catalog Fall
The sample of 46 members includes two spectroscopically
2008 (mag I = 25 limited) gathers the photometric redshifts
confirmed quasars from the SDSS catalog (Hewett & Wild
measuredfromthoseauthors.
2010).Fromthepointofviewoftheradiomorphologyclassifi-
cation,thesampleincludes18compact(ormarginallyresolved
at the resolution provided by the COSMOS-VLA images) ra-
dio structures, six slightly extended sources, one intermediate
3. Thesample FR I/FR II, and 21 FR IIs (see Sect. 7.1). Nine of the sources
thatweselectedaspartofthisworkhavepropertiesthatsatisfy
The aim of the project is to select the RL AGN population in
theselectioncriteriaofC09.Theseobjectsweremostlikelynot
theCOSMOSfieldathighredshifts.Withrespecttotheobjects
included in that sample because those authors used their radio
considered in C09 and studied by B13, we relax the selection
fluxintheversionoftheFIRSTcatalog,whichwasnotlistedas
criteria to include not just high redshift FR I candidates, but
>1mJy.Thisisduetothecontinuouslyongoingupdatingofthe
all radiosourceslikely to be associated with galaxiesat z (cid:2) 1. FIRSTcatalogovertheyears7.
DifferentlyfromC09,wedidnotsetahighradiofluxlimit(they
onlyincludedobjectswithaFIRSTfluxrangingbetween1and
13 mJy), and we also decided not to exclude u-band dropout 4 We consider a radius of 5100 arcsec because it corresponds to the
radiusofacircle,whichcircumscribesthe“squared” COSMOSfield.
galaxies.
Thisallowsustoincludealltheradiosources,whichsatisfyourselec-
We then simply search for sourceswith FIRST radio emis- tioncriteria,butarelocatedattheedgesoftheCOSMOSfield.
sionlargerthan1mJyovertheCOSMOSfield.Thetotalnum- 5 ThisnumbercorrespondstoeachFIRSTradiodetection.Therefore,
ber of FIRST radio detection sources in a circular area of itdoesnotcorrespondtothetotalnumberofradiosources,sincedouble
oreventripleFIRSTradiosourcesarepresent.
6 Toidentifythesources, weuseanumber ranging from1to56for
2 TheCOSMOScatalogisderivedfromacombinationoftheCFHTi∗ simplicity.Thisnumberdoesnotcorrespondtothenomenclatureused
andSubarui+imagestowhichtheauthorsreferasI-bandimages byC09.ThesourcesselectedbyC09arenamedas“COSMOS-FRI”.
3 http://irsa.ipac.caltech.edu/cgi-bin/Gator/nph-dd 7 http://sundog.stsci.edu/first/catalogs/
A76,page3of32
A&A567,A76(2014)
Table1.Identifiedradiogalaxies.
n RadioID RA Dec N F F Radiomorph HostID mag z z
c FIRST NVSS i photo spec
1 J100046.91+020726.5 100046.944 +020726.02 1 1.79 2.6 compact 766333 22.28 1.2101.50 1.1577a
1.19
2 J100109.28+021721.7(2) 100109.280 +021721.49 1 3.21 3.7 FRII − <26.72 − −
3 J100101.26+020118.0 100101.258 +020116.98 1 1.68 <2.5 compact 756907 24.97 1.8762.35 −
1.45
4 J100016.57+022638.4 100016.575 +022638.28 1 5.18 5.1 compact − 25.90 − −
5 J100114.85+020208.8(4) 100114.942 +020221.48 2 4.78 6.2 FRII 754529 21.21 1.1201.15 0.9707a
1.10
6 J100114.12+015444.3(6) 100114.542 +015451.72 2 4.99 6.2 FRII 526188 23.30 1.4261.48 −
1.35
7 J100058.05+015129.0(4) 100058.107 +015141.15 2 10.10 12.4 FRII 534525 25.24 1.4552.29 −
1.26
8 J100201.17+021327.1(3) 100201.235 +021326.67 1 4.89 6.3 FRII 952745 21.45 0.8320.85 0.8357a
0.81
9 J095959.16+014837.8(2) 095959.127 +014837.79 1 7.70 8.4 FRII 591011 25.80 − −
10 J100120.06+023443.7 100120.090 +023443.62 1 9.07 9.6 compact 1425414 26.82 − −
11 J100140.12+015129.9(4) 100139.193 +015139.49 1 7.85 11.1 FRII 509607 23.22 0.9591.01 −
0.93
12 J100006.17+024000.5 100006.137 +024000.13 1 3.47 * compact − 25.95 − −
13 J100007.29+024049.8(2) 100007.294 +024049.79 1 3.47 * FRII 1703047 23.99 1.2381.43 −
0.93
14 J095835.44+020543.7 095835.473 +020543.81 1 11.73 13.1 compact 845386 24.58 1.2591.91 −
1.10
15 J095927.25+023729.2(3) 095927.221 +023737.32 1 1.94 5.9 FRII 1490892 22.66 1.0061.04 −
0.98
16 J100137.77+014811.7 100137.793 +014811.38 1 2.60 <2.5 compact 517639 21.87 0.8360.86 0.8442b
0.81
17 J100230.11+020912.4(5) 100229.915 +020910.72 2 6.40 6.3 FRII 939988 24.08 1.4581.58 −
1.32
18 J100007.90+024315.4(4) 100007.835 +024310.52 2 9.99 12.0 FRII 1695922 22.38 1.4831.63 −
1.44
19 J100218.03+015555.7 100218.083 +015556.85 1 1.04 <2.5 compact − 21.52 − −
20 J100212.06+023134.8(4) 100211.867 +023134.40 2 16.28 17.4 FRII 1408636 23.81 1.0141.21 −
0.91
21 J100159.82+023904.8 100159.861 +023904.53 1 2.67 4.3 compact 1633838 22.40 0.8130.84 −
0.79
22 J095837.11+023549.0 095837.168 +023549.37 1 1.05 <2.5 compact 1519463 24.91 2.6042.86 −
2.25
23 J100028.31+013507.8(5) 100026.611 +013527.67 2 14.65 26.6 FRII 115652 22.42 0.8350.86 0.83933b
0.82
24 J095826.95+023711.7 095826.966 +023711.55 1 2.24 3.0 compact 1516040 25.63 − −
25 J100124.09+024936.3(4) 100124.122 +024936.58 1 3.39 3.9 FRI/FRII 1874867 21.21 0.8250.84 0.82510b
0.81
26 J095756.52+022717.3 095756.541 +022717.25 1 2.57 2.3 compact 1319327 21.14 0.7310.75 −
0.72
27 J095908.87+013606.6 095908.861 +013606.64 1 5.46 6.5 compact 159456 25.22 − −
28 J095839.24+013557.8(4) 095839.742 +013556.85 1 2.56 4.9 FRII 182240 24.27 1.6762.06 −
1.40
29 J095821.65+024628.1 095821.700 +024628.07 1 4.62 10.3 compact-QSO 1738294 19.35 0.7810.79 1.4050c
0.77
30 J095838.01+013217.1 095837.991 +013217.12 1 4.21 4.3 extended − <26.10 − −
31 J095835.71+025328.9 095835.719 +025328.67 1 3.61 3.5 extended 1957693 25.84 − −
32 J095738.38+023837.7∗ 095738.375 +023837.62 1 2.78 3.2 extended 1780946 24.35 − −
33 J100331.82+014901.4∗ 100331.849 +014901.77 1 1.08 2.7 extended − <25.40 − −
34 NVSSJ100250+013017 100250.681 +013019.26 1 8.61 7.0 extended 61719 24.07 1.3881.46 −
1.26
35 J100217.97+015836.4 100217.988 +015836.13 1 26.83 26.3 compact 714756 21.63 0.9020.91 −
0.89
36 J095803.21+021357.7 095803.223 +021357.58 1 24.71 25.2 compact 1103009 24.89 2.2182.77 −
1.91
37 J095908.32+024309.6(4) 095907.629 +024302.59 3 55.92 59.4 FRII-QSO 1721832 19.20 0.7870.80 1.3197c
0.78
38 NVSSJ095758+015832∗ 095800.807 +015856.75 3 43.91 52.2 FRII 887322 23.89 2.3682.76 −
2.19
39 J100252.88+015549.7 100252.887 +015549.66 1 16.65 16.7 compact 477930 25.72 − −
40 J095908.95+024813.4(3) 095909.143 +024816.45 2 20.66 28.8 FRII 1947189 23.06 1.1111.15 −
1.08
41 J095742.30+020426.0 095742.313 +020425.97 1 18.63 18.5 extended 873336 22.39 0.8580.87 −
0.85
42 J100153.77+024954.0 100153.822 +024953.94 1 16.77 16.0 compact 1852665 23.29 1.1121.24 −
1.06
43 J100303.66+014736.0(6) 100304.903 +014724.21 2 23.88 32.6 FRII 454341 22.97 1.1921.37 −
0.89
44 J100251.11+024248.5(4) 100250.858 +024250.14 2 176.05 174.3 FRII 1599142 22.95 1.1851.21 −
1.16
45 J095741.10+015122.509(6) 095739.795 +015141.87 3 31.17 43.2 FRII 657685 22.59 0.8201.01 −
0.79
46 J095822.30+024721.3(5) 095822.881 +024728.14 2 17.36 22.7 FRII 1736088 22.57 0.9070.94 0.8784a
0.85
Notes.Columndescription:(1)identificationnumber;(2)COSMOS-VLA(LargeProject)IDnumberoftheobject(Schinnereretal.2007).Incase
ofmultipleobjects,thenumberofcomponentsisshownonthesuperscript.Theobejctsmarkedwith∗areidentifiedintheCOSMOS-VLADeep
Project (Schinnerer et al. 2004). The object 34 has the NVSSID; (3)−(4) right ascension and declination of (one of the components of) FIRST
radiosource;(5) numberofmatchesfoundintheFIRSTcatalogassociatedwiththesameradiogalaxy;(6) (total)FIRSTradioflux(mJy)ofthe
entireradiosource;(7)NVSSradioflux(mJy).Thetwoobjects,12and13,areincludedinthesameNVSSradiosourceswithafluxof7.6mJy.
(8)COSMOS-VLAradiomorphology;(9)IDnumberofthehostassociatedwiththeradiogalaxyfromtheCOSMOSIntermediateandBroadBand
PhotometryCatalog2008;(10)Subarui+,CFHTi∗orACS/HSTF814WmagnitudeofthehostgalaxyfromthetheCOSMOScatalogormeasured
ontheimage;(11)photometricredshiftwith99%confidence-levelerrors;(12)spectroscopicredshiftfromthezCOSMOScatalog(Lillyetal.2007)
markedwith(a),theMagellancatalog(Trumpetal.2007)markedwith(b),andSDSSquasar(QSO)spectra(Hewett&Wild2010)markedwith(c).
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R.D.Baldietal.:Theradio-loudAGNpopulationatz(cid:2)1intheCOSMOSfield
Table2.Radiogalaxieswithnoclearhostidentification.
n RadioID RA Dec N F F Radiomorph
c FIRST NVSS
47 J100102.38+020529.1(3) 100102.402 +020526.77 1 2.68 2.3 complex
48 J095949.80+015650.7(2) 095949.787 +015649.97 1 1.77 <2.5 FRII
49 J100049.58+014923.7(4) 100048.705 +014922.29 2 5.48 12.4 composite
50 J100129.35+014027.1(2) 100129.328 +014027.01 1 1.69 7.2 complex
51 J095856.19+024127.9 095856.220 +024127.39 1 3.67 4.2 compact
52 J095901.52+024740.6(4) 095901.632 +024739.82 2 4.69 6.7 FRII
53 J100320.60+021608.9∗ 100320.613 +021608.99 1 3.38 3.9 compact
54 J100245.39+024519.8(2) 100244.947 +024500.99 2 20.00 28.2 FRII
55 J095822.93+022619.8(6) 095824.989 +022649.36 2 84.73 103.2 FRII
56 J100243.20+015942.1(3) 100242.622 +015937.74 2 53.52 58.7 FRII
Notes.Columndescription:(1)identificationnumberincreasingwiththedistancefromthecenteroftheCOSMOSfield;(2)COSMOS-VLA(Large
Project)IDnumberoftheobject.Incaseofmultipleobjects,thenumber ofcomponentsisshownonthesuperscript.Theobejctsmarkedwith
∗areidentifiedintheCOSMOS-VLADeepProject;(3)−(4) right ascension and declination of (oneof thecomponents of) FIRSTradio source;
(5) number ofmatchesfoundintheFIRSTcatalogassociated withthesameradiogalaxy; (6) (total)FIRSTradioflux(mJy) oftheentireradio
source;(7)NVSSradioflux(mJy);(8)COSMOS-VLAradiomorphology.
The COSMOS collaboration performed a similar radio se- Afurthertoolofidentificationisgivenbythehigh-resolution
lectionintheCOSMOSfield,namedtheVLA-COSMOSLarge HST/ACS images, which allow us to locate the host associ-
Project (Schinnerer et al. 2007). It consists of identification of ated with the radio source and distinguish it from possible
radio-emitting sources at 1.4 GHz that are observed with the mis-identifiedcompanions.All the sources, but8 objects,have
VLA at a higher radio resolution (A and C arrays) than the HST/ACSimages.Furtherfiveobjectsarenotbrightenoughto
NVSSandtheFIRSTthatweused.However,ourselectionpro- be detected in the HST/ACS maps. For these objects, i+-band
cedure is more sensitive to low brightness radio sources than Subaruimagesrepresentthebestalternativesfortheirlargersen-
that used by the VLA-COSMOS Large Project. In fact we de- sitivitydespitelowerresolutionthanHST/ACS.Foronesource
tect radio sources in FIRST which do not show emission in (namely 33), HST/ACS and i+-band Subaru images are not
the VLA-COSMOS images. Most of our sources are included presentbuti∗-bandCFHTobservation.
in the VLA-COSMOS catalog (Table 1). However, those not Letusfocusontheidentifications.Twenty-onetargetsshow
included are still visible in the VLA-COSMOS radio maps. a compact(unresolved,or slightly resolvedat the resolutionof
Thereforeour sample does not totally overlap with the catalog theVLA-COSMOSsurvey,1(cid:4).(cid:4)5),andanothersixsourcesshow
createdbySchinnereretal.(2007).Thissuggeststhatourcare- extended structures on a scale of ∼3−4(cid:4)(cid:4). For such objects, we
ful visual inspection is fundamental to identify weak sources. startthemultibandidentificationprocessbylookingforaI-band
Furthermore, differently from the VLA-COSMOS catalog, we counterparttotheradiosourcewithina0(cid:4).(cid:4)3radiusfromthera-
performamulti-bandcross-matchingtoisolatethedistantradio dio position in the COSMOS catalog. We then check the co-
sourcesandexcludethepossiblestar-forminggalaxies. spatiality of the position of the optical host, the VLA radio
sourceandtheIRACinfraredemission.Ifthisoccurswithasep-
arationoflessthan0(cid:4).(cid:4)5(theastrometryaccuracyofIRACmaps),
4. Multibandcounterpartsidentification thethreecounterpartsareconsideredasassociatedwiththesame
source.Themajorityoftheradiosourcesareopticallyidentified
The radio morphology of the source plays a fundamental role atdistancessmallerthan0(cid:4).(cid:4)1fromtheradiosource.Wealsouse
inthisprocedure.Toinspectthatofoursources,wemainlyuse the Spitzer data to search for the infraredcounterparts.In such
theradiomaps(180arcsec,correspondingtoasizeof∼1.5Mp a case, we use a larger search radius (2(cid:4)(cid:4)) due to their coarser
atz = 1)fromtheVLA-COSMOSLargeandDeepProjectsin resolutions. For two compact radio sources the host identifica-
comparisonwith the low-resolutionFIRST and NVSS images. tion failed because of the presence of multiple optical sources
The VLA-COSMOS images provide sufficient angular resolu- fallingwithintheradiostructure.InFig.A.1,weshowthesuc-
tion to recognize the presence of radio cores, which are useful cessful identification,while the two “failed” objects are shown
(butnotnecessary)toidentifythecorrespondinghostgalaxies. inFig.A.3.
The VLA-COSMOS radio morphologies of the selected Considering the sources, which show extended radio emis-
sample are variegated (see Figs. A.1 and A.2 and Table 1). sion,thesampleselectedinthisworkalsoincludessourceswith
The 21 FR IIs with their classical double-lobed structures a FR II morphology,which is contraryto the C09 sample. The
clearlystandout.Onesource,namely25,showsanintermediate opticalidentificationfor thoseextendedradioobjectsisclearly
FRI/FRIIradiomorphology,sinceitstwo-sidedjetsshowsur- moredifficultthanforthecompactones.Tostrengthenthehost
facebrightnesspeaksapproximatelyathalfofitsradioextended identification,wevisuallycheckthecounterpartsineachimage
size.Conversely,no“bonafide”FRIstructuresarepresent.Half availablefromtheUVtotheIRband.
ofthesampleappearsascompactsources(unresolvedorslightly In 11 cases, the radio source has a triple structure with a
resolved at the resolution of the VLA-COSMOS survey, 1(cid:4).(cid:4)5). centralunresolvedradiocomponent(mostlikelytheradiocore)
Sixobjectsshowslightlyelongatedradiostructures.Onequasar associatedwithanoptical/IRcounterpart(seeFig.A.1).Inthese
is associated with a FR II, while the other hasa compactradio cases, we proceed as above, using the location of the central
morphology.Unfortunately,weleaveouttensourcesbecausewe componentasreferencefortheoptical/IRcounterpart(Fig.A.2).
failinthehostidentification.Thesesourcesshowcompact,com- Conversely,theassociationislessobviousintheremaining
plex,andFRIIradiomorphologies(seeFig.A.3andTable2). 18radiosources.Thisisthecaseoftwoobjectswithacomplex
A76,page5of32
A&A567,A76(2014)
radio morphology(object 49 and 50), 14 double radio sources measure a 2σ flux upper limit. Six sources are visible in the
(without radio core), or two sources with a triple morphology, optical band (Subaru or CFHT), but they do not reach the flux
butwherethecentralcomponentisextended.Forthetwotriple threshold of the COSMOS broadband photometry catalog, are
sources(objects7and17),thecentralradiocomponentindicates contaminatedbya companion,orarewronglyidentifiedbythe
the approximate location of the radio core, and it is probably COSMOS catalog. In only three cases (namely, 2, 30, and 33)
elongatedduetothe contributionofa radiojet. We lookforan instead, no i-band identification is possible, but the identifica-
optical/IRhostinthisarea,andindeed,asinglebrightgalaxyis tion with the radio source is nonethelessstraightforwardin the
foundinbothcases,whichweidentifyasthecounterpart. infraredimages.
For the remaining 14 FR IIs, we look for the host galaxy As alreadyoutlinedinB13 insomecases, theGALEXand
along a straight line connecting the hot spots in the VLA- MIPS catalog photometry returns apparently wrong identifica-
COSMOS images. In eight cases, we identify the brightestop- tion. However, we visually check all the counterparts to con-
tical/IR counterpart as host galaxy, which also corresponds to firm the UV and IR identifications. If a source is not detected
the closest object to the center of the radio structure as shown in GALEX, we prefernotto includeupperlimits in our analy-
in Fig. A.2. Conversely, there is no visible optical/IR source sis,becausethecorrespondingNUVorFUVfluxissubstantially
between the lobes in objects 47, 48, and 52; finally, the asso- higherthanthedetectionsatlargerwavelengthsandarenotuse-
ciation is not univocal in objects 54, 55, and 56, since several fultoconstraintheSED.Forsixsources,wemeasurethe24μm
optical/IR sources are present. These six objects are shown in flux when not detected by the catalog. Furthermore, we com-
Fig.A.3withthetwocomplexradiosources,whichweexclude putethephotometrycorrectiontotheCOSMOSUKIRTJ-band
fromthesample. magnitudesasobservedbyB13.
Clearly, while the identifications of the hosts of ten (two Thecorrected3(cid:4)(cid:4)-aperturephotometricmeasurementsofall
triples and eight doubles) FR II are plausible, which have ex- 46sourcesaretabulatedinTablesA.1andA.2andincludesall
cluded the less convincing ones, we cannot exclude that there the multiband magnitudesassociated with the optical/IR coun-
mightstillbespuriousassociations.Thisismostlikelythecase terpartsoftheradiogalaxies.
of radio sources of large angular size and where the host is
far from the center of the radio structure, such as object 46.
5. SEDfitting
However,inmostcasestheproximityoftheradiolobessignifi-
cantlyreducessucharisksincethehostsearchareaislimitedto The SEDs are derived by collecting multiband data from the
afewsquaredarcseconds. FUV to the MIR wavelengths. Since not all of the objects are
Summarizing,theidentificationissuccessfulfor46objects. detectedintheentiresetofavailablebands,thenumberofdat-
All butsix are presentin the COSMOS broadbandphotometry apoints used to constrain the SED fitting ranges from 19 (ob-
catalog. Furthermore, each radio source has a Spitzer infrared ject29)to2(object33).However,theupperlimitstothemag-
counterpart.For the identified objects, we take the 3(cid:4)(cid:4)-aperture nitudes, especially in blue and IR band, can, at least, roughly
photometricmagnitudesfrom∼0.15μmto24μmfromthesecat- constrainthecontributionoftheYSPanddustcomponent.
alogs.Thecarefulvisualinspectionoftheimagesoftheidenti- As discussed in B13, the residuals of the SED fitting be-
fiedsourcesenablesustorecognizethepresenceofthreesources comessmallerwhenasecondstellarcomponentanddustemis-
associatedwithastellar-likeopticalcounterpart(seeSect.6.2for sion are included. Considering the larger number of parame-
details). This might indicate a compact nucleus that outshines ters in the fit than in the case of a single stellar population
thehostgalaxy,asignofthepresenceofaquasarinthecenter. (such as Hyperz, Bolzonella et al. 2000), the fitting improve-
Two of them are spectroscopically confirmed quasars (namely, mentisbasicallybecausetwodifferentstellarpopulations,typ-
29 and 37). Unfortunately, the third object (namely, 35) does ically oneyoungerandoneolder(YSPandOSP, respectively),
not have any available spectroscopic information. It is associ- canbetterreproducethecomplexmorphologyoftheSED,which
atedwithacompactradiosource.Allthesourcesaredetectedin mightrepresentthecomplexstarformationhistoryofthegalaxy.
opticalband,butthreeobjects(namely,2,30,and34)are only Furthermore, the dust emission is necessary to account for the
detectedatlongerwavelengths. MIRcomponent,whichisnotcompatiblewithstellaremission.
The COSMOS catalogs are affected by the limitations typ- The simultaneousinclusion of these componentsis allowed by
ical of multiband surveys, such as misidentification of targets our developed code 2SPD (see B13 for details on the code),
with a close neighbor or the contamination by bright sources. which we prefer to use in this work rather than Hyperz. Since
We thencheckthe multibandcounterpartidentificationofeach we use stellar templates, we left out the two spectroscopically
source by visually inspecting its multibandimages, rather than confirmedquasarsfromthisprocedure.
blindlyusingthedataprovidedbytheCOSMOScatalog.More The stellar synthetic models used are from Bruzual &
specifically,weidentifyallobjects,wherei)nearbysourcesare Charlot (2009, priv. comm.) and Maraston (2005) and are the
present within the 3(cid:4)(cid:4) radius used for the aperture photometry two sets differingfor their initial mass function(IMF;Salpeter
(thuscontaminatingthegenuineemissionfromtheradiogalax- 1955; Kroupa 2001; Chabrier 2003). We considered models
ies) or when ii) the counterparts to the i-band object do not of solar metallicity, single stellar populationwith ages ranging
correspondto the same object over the various bands. In these from 1 Myr to 12.5 Gyr. We adopt a dust-screen model for
circumstances, we do the following: 1) in case of contamina- the extinction normalized with the free parameter A and the
V
tion from a nearby source(s), we subtract from the flux, which Calzettietal.(2000)law.Ontheotherhand,wemodelthedust
results from the photometry centered on the radio source, the component with a single (or, in some cases, two) temperature
emissionfromtheneighbor(s);2)weperformanew3(cid:4)(cid:4)-aperture black-bodyemission.
photometry,thatisproperlycenteredonthepositionoftheradio The code 2SPD searches for the best match between the
source.When needed,we appliedthe requiredaperturecorrec- sum of the different components and the photometric points
tions(seeB13). by minimizing the appropriate χ2 function. The 2SPD returns
When an object cannot be separate from a close compan- the following free parameters: z, A , the age of the two stellar
V
ion or when the counterpart is not visible in a given band, we populations,the temperatureof the dustcomponent(s),and the
A76,page6of32
R.D.Baldietal.:Theradio-loudAGNpopulationatz(cid:2)1intheCOSMOSfield
normalizationfactors.Forthenineobjectswhosespectroscopic
redshiftsareavailable,weprefertokeepfixedtheirredshiftsas
theobservedvalues,sincethephoto-zobtainedarealwayscon-
sistent with the spectroscopic redshifts in the case of free pa-
rameter,asperformedinB13.Fromthefit,wemeasurethestel-
lar mass content of the two stellar populations at 4800 Å rest
frame. However, caution should be exerted before associating
thesevaluestophysicalquantitiesbecauseofdegeneracyinthe
parameterspace,apartfromthephotometricredshifts(Table3).
Furthermore,since the infraredexcess is not often evident, the
dustemissionisusuallypoorlyconstrained.Wethereforeprefer
nottogiveanyparticularphysicalmeaningtoeachvalueofthe
dustparameters(temperatureandluminosity).We returnto the
dustpropertiesinmoredetailinSect.6.3.
To estimate the errorson the photo-zand mass derivations,
we measure the 99%-confident solutions for these quantities.
This is computed by varying the value of the parameter of in-
terest (photo-z or mass) until the χ2 value increases by Δχ2 =
6.63, which corresponds to a confidence level of 99% for that
parameter.
FigureA.4showstheplotsoftheSEDfitting,whileTable3 Fig.1. Comparison of the photometric-z measured with 2SPD with
presentstheresultingparametersofthefit. those obtained by the COSMOS collaboration (Ilbert et al. 2009;
Salvatoetal.2009).Thedashedlineisthebisectoroftheplane.
6. Results
Totestthereliabilityofourphoto-zderivation,wefirstcom-
pare the photometricredshiftsmeasured with 2SPD with those
TheSEDmodelingprocesshasbeenperformedforall46objects
obtained with the template-fitting technique performed by the
(exceptforthespectroscopically-confirmedquasars,namely29
COSMOScollaboration(Ilbertetal. 2009;Salvatoetal. 2009)
and37)byusingthetemplate-fittingtechniques,2SPD.Wealso
(Fig. 1). Obviously, we do not consider the objects 10, 22, 33,
modeltheSEDofobject35,althoughitsopticalpoint-likemor-
and35forthecomparison(forthereasonsexplainedinSect.6);
phologysuggestsanidentificationasaquasar.
thesourcesarenotincludedintheCOSMOSphoto-zcatalogand
TheSEDsforapproximatelyhalfofthesampleshowa“bell”
thosewhosespectroscopicredshiftsareavailable.Generally,our
shape. This behavior is ascribed to the dominance of the OSP
photometricredshiftsareconsistentwiththeCOSMOSphoto-z
overtheYSPanddustcomponent(s).However,theotherhalfof
thesampleshowexcessesinUVand/orMIRwavelengths. within error. On average, our photo-z uncertainties are slightly
smallerthanthoseprovidedbytheCOSMOScollaboration.This
Generally, the number of photometric detections is crucial
indicates that the redshift does not depend much on the single
fortheSEDfittingreliability.Thecaseof33isaclearexample.
changes in the datapoints. However, our SEDs are more real-
Theobjectisdetectedonlyin3.6andand5.8μmIRACbands,
istic because of our careful visual inspection of the multiband
because the source is on the border of the COSMOS field. counterpartidentifications. The normalizedredshift differences
Furthermore, since the OSP is the component, which fits the (Δz/(1+z) betweenour valuesand the COSMOS photo-z)are
SED on a larger range of wavelengths than YSP and dust, the
smaller than 0.08, which is similar to what B13 found, for all
dominance of the OSP over the other two components deter- but three objects that reach Δz/z ∼ 0.22−0.27 (objects 6, 13,
minesthequality/reliabilityofthemodeling.Anotheraspectcru-
and18).
cial for the fitting is the intrinsic prominence of some spectral
Since the sample includes spectroscopically-confirmed
propertiesoftheOSP:the4000Åbreakandtheblueorinfrared
quasarsandotherpotentialquasarswhoseSEDsappearpower-
partofthespectrum.IfthesefeaturesarenotevidentintheSED
lawdominated,weusethemethodtoderivethephotometricred-
becausetheYSPand/ordustcomponentdominateovertheOSP,
shifts, as introduced by Richards et al. (2001a,b) for quasars.
the resulting fit is not unique and, thus, is not reliable. This is
Theyconstructanempiricalcolor-redshiftrelationbasedonthe
the case of the objects10,22 and 35.Therefore,for these four
median colors of quasars from the SDSS survey as a function
radiosources(includingobject33),wedonotconsidertheSED
of redshift.Photometricredshiftsare then determinedby mini-
modelreliable,whichweobtainwiththe2SPDtechnique. mizingtheχ2 betweenallfourobservedcolorsandthemedian
colors(obtainedbycombiningthefiveSDSSmagnitudes,u(cid:4),g(cid:4),
r(cid:4),i(cid:4),andz(cid:4))asafunctionofredshift.
6.1.Photometricredshifts
We applythismethodtothesources,whichshowa quasar-
Thephotometricredshiftsobtainedwith2SPD(Table3)forthe like SED and are detected in at least 2 SDSS bands, which
46 objects selected in this work range between ∼0.8 and 2.4. include objects 22 and 35 (object 10 is excluded for this rea-
Thirteen out of 46 sources are not present in the COSMOS son). As a sanity check, we include the two spectroscopically-
photo-zcatalogmainlybecausetheirI-bandmagnitudesarebe- confirmedquasars,namely29and37,in thisanalysis.We also
yond the I = 25 limit of the COSMOS Photometric Redshift decided to analyze again objects with similar spectral shapes
Catalogand,marginally,becauseofthemisidentificationofthe foundbyB13,namelyCOSMOS-FRI32,37,and226,because
photometriccounterparts(seeB13fordetails).Forsuchobjects, they are potentially quasars for their power-law spectral be-
we do not have another photo-z measurement apart from our havior and the spectroscopically-confirmed quasar, COSMOS-
derivation. FRI236.
A76,page7of32
A&A567,A76(2014)
Table3.2SPDSEDfitting.
ID Redshift YSP OSP logM∗ Dust IRexcess UV
zphot Age AV fYSP LogM∗ Age AV Tdust Ldust LIRexc. α8−24 LUV
1 1.1577s 0.004 0.73 21.9% 0.14% 2.0 0.72 11.31+0.04 118−528 224.5−213.8 45.74 −0.87 43.51
−0.04
2 1.767+0.570 0.006 1.24 23.8% 0.14% 3.0 1.21 10.67+0.05 181 17.0 <43.96 <42.00
−0.236 −0.05
3 1.983+0.34 0.001 1.07 21.8% 0.51% 2.0 0.81 10.79+0.06 166 29.4 44.15 >−0.42 42.98
−0.37 −0.05
4 1.104+0.76 0.003 1.24 6.6% 0.04% 3.0 0.94 10.32+0.16 179−468 24.8−2.5 44.41 0.62 <41.43
−0.28 −0.18
5 0.9707s 0.002 0.76 27.3% 0.49% 4.0 0.10 11.17+0.09 134−911 3.8−6.8 44.22 −0.53 43.80
−0.10
6 1.963+0.24 0.003 0.49 32.1% 0.30% 3.0 0.21 10.85+0.05 189 11.0 43.79 >−0.38 43.47
−0.28 −0.05
7 1.384+0.16 0.004 1.31 28.1% 0.09% 4.0 1.30 10.89+0.06 123 4.8 <43.49 42.19
−0.06 −0.06
8 0.8357s 0.002 2.80 10.3% 1.7% 4.0 0.13 11.59+0.07 151−769 2.8−4.2 <44.10 <42.20
−0.07
9 2.152+0.17 0.003 0.98 10.4% 0.22% 1.0 0.62 10.60+0.05 200 26.2 <44.15 42.83
−0.44 −0.06
10 1.268+0.30 0.002 1.5 34.9% 1.88% 1.0 1.19 9.42+0.08 221−720 3.8−1.8 44.11 −0.24 41.65
−0.33 −0.08
11 1.018+0.15 0.004 1.38 9.8% 0.18% 0.8 1.21 10.69+0.06 122 4.2 <43.44 42.23m
−0.08 −0.06
12 1.860+0.73 0.009 1.47 48.8% 2.09% 2.0 1.19 10.49+0.10 119 10.2 <43.66 42.38
−0.56 −0.09
13 1.018+0.02 0.004 1.61 13.0% 0.44% 0.7 0.99 10.16+0.04 128 2.3 <43.16 41.88m
−0.05 −0.04
14 1.377+0.27 0.001 1.09 3.3% 0.09% 2.0 0.54 10.92+0.07 131 10.3 43.87 >−0.12 42.34
−0.103 −0.08
15 1.015+0.03 0.004 1.45 0.6% 0.02% 1.0 0.58 10.76+0.03 139 2.1 <43.15 <42.06
−0.02 −0.03
16 0.8442s 0.003 1.10 1.6% 0.03% 1.0 0.71 10.78+0.06 124 3.1 43.26 >−0.59 <42.22
−0.06
17 1.391+0.22 0.002 0.84 7.4% 0.14% 2.0 0.46 10.89+0.04 185 9.3 <43.83 42.87
−0.11 −0.04
18 1.193+0.123 0.008 1.36 59.0% 3.15% 2.0 0.64 10.94+0.03 198−643 26.6−3.3 44.71 0.43 43.30
−0.16 −0.04
19 0.932+0.03 0.003 2.26 5.3% 0.33% 2.0 0.28 11.26+0.03 110 8.9 43.66 >0.91 <42.20
−0.01 −0.03
20 1.016+0.20 0.001 0.88 4.6% 0.16% 0.9 0.86 10.33+0.08 210 4.5 <43.52 42.33m
−0.09 −0.08
21 0.894+0.06 0.004 0.91 3.8% 0.04% 2.0 0.27 10.71+0.04 196 3.2 <43.42 42.20m
−0.062 −0.04
22 2.393+1.3 0.002 0.56 31.5% 2.21% 0.9 0.07 9.77+0.15 181−932 3.0−6.6 44.40 0.28 43.32
−0.88 −0.17
23 0.8393s 0.004 1.17 5.6% 0.12% 0.8 0.79 10.50+0.02 135 2.6 <43.30 42.25m
−0.02
24 2.006+0.30 0.002 0.84 7.1% 0.10% 2.0 0.71 11.08+0.04 178 98.1 44.69 >0.66 42.91
−0.27 −0.04
25 0.825+0.03 0.003 3.02 25.8% 3.04% 2.0 0.60 11.17+0.02 134 3.1 43.27 >2.50 <41.98
−0.03 −0.02
26 0.830+0.11 2.0 0.10 11.04+0.06 125 2.9 <43.32 <42.07
−0.11 −0.06
27 2.523+0.68 0.004 0.57 10.7% 0.17% 1.0 0.30 10.68+0.07 131 33.8 <44.17 43.22
−0.32 −0.07
28 1.788+0.43 0.005 0.69 34.7% 0.67% 2.0 0.08 10.51+0.09 212−505 5.2−1.9 44.12 −0.23 43.30
−0.33 −0.08
29 1.4050s QSO
30 2.268+0.56 0.005 1.53 49.3% 0.80% 2.0 1.22 10.74+0.05 161 25.7 <44.16 42.53m
−0.21 −0.05
31 1.698+0.49 0.001 1.08 15.1% 0.25% 2.0 1.04 10.65+0.05 227 16.9 <44.06 42.57
−0.19 −0.05
32 1.067+0.32 0.003 2.08 64.8% 3.27% 1.0 1.75 10.08+0.07 206 5.2 <43.59 42.05m
−0.10 −0.07
33 1.421+0.67 0.003 1.32 4.9% 0.03% 3.0 1.01 10.92+0.07 179 19.1 <44.02 <41.79
−0.61 −0.07
34 1.402+0.31 0.002 0.67 0.8% 0.03% 0.9 0.30 10.65+0.23 204−731 14.4−18.0 44.61 −1.08 <42.63
−0.32 −0.29
35 1.028+0.27 0.006 0.45 59.2% 0.96% 3.0 0.09 10.71+0.06 206−625 5.1−7.4 44.34 −0.69 43.89
−0.17 −0.06
36 2.255+0.70 0.04 0.31 34.3% 1.50% 2.0 0.71 10.91+0.07 155 25.1 <44.09 43.37
−0.35 −0.07
37 1.3176s QSO
38 2.355+0.45 0.009 0.47 22.5% 0.48% 2.0 0.31 11.09+0.04 132 67.0 44.42 >0.58 43.70
−0.16 −0.04
39 1.851+0.36 0.006 1.24 11.0% 0.16% 3.0 0.34 10.94+0.07 155 17.7 <43.94 42.34m
−0.30 −0.06
40 1.110+0.24 0.7 0.73 10.70+0.12 155 4.6 <43.51 <42.24
−0.20 −0.11
41 1.028+0.07 0.001 0.14 3.0% 0.16% 0.07 1.40 10.22+0.19 211−646 26.4−1.9 44.69 0.15 43.27
−0.18 −0.07
42 1.137+0.44 0.003 1.10 4.4% 0.10% 0.9 0.68 10.75+0.16 156 4.9 <43.66 42.58m
−0.30 −016
43 1.247+0.46 0.005 1.00 2.9% 0.06% 0.9 0.64 11.03+0.19 96 9.9 <43.63 42.68m
−0.44 −0.32
44 1.062+0.14 0.003 0.15 4.0% 0.04% 1.0 0.48 10.61+0.03 189−644 8.2−1.6 44.37 0.53 43.12
−0.05 −0.04
45 0.918+0.07 0.003 1.04 2.0% 0.04% 0.8 0.94 10.74+0.05 101 4.9 <43.35 42.28m
−0.07 −0.05
46 0.8784s 0.007 1.35 10.7% 0.49% 0.8 0.78 10.47+0.09 100 4.4 <43.29 42.27m
−0.13
Notes.ResultsfromtheanalysisoftheSEDswith2SPD.Columndescription:(1)IDnumber oftheobject;(2)photometricredshiftmeasured
with2SPD;(3)−(6)ageinGyr,A ,fluxfractionandmassfractionoftheyoungstellarpopulation(YSP)at4800Årestframe;(7),(8)ageinGyr
V
and AV oftheoldstellarpopulation(OSP);(9)thetotalstellarmassofthegalaxyin M(cid:3);(10),(11)theeffectivetemperature(inK)oftheone
ortwodustcomponentsandtheirluminosities,Ldust(inunitsof109 L(cid:3));(12),(13)theinfraredexcessluminosity(inergs−1)definedinthetext
(Sect.6.3)andthespectralindexmeasuredontheinfraredexcessat8and24μm;(14)UVluminosityat2000Å intherestframeinergs−1.The
marginalUVexcessesaremarkedwitham.TheobjectswiththeIDinboldcharachter(namely,10,22,and33)areexcludedfromthefinalsample
fortheirambiguousSEDproperties.TheQSOarethespectroscopically-confirmedquasars.
Table 4 reportsthe SDSScolorsforthese eightobjectsand thantheunityarenotconsideredstatisticallysignificant.Forthe
Fig. 2 shows their χ2 curves. The χ2 minima that are smaller three spectroscopic quasars (29, 37 and COSMOS-FR I 236),
A76,page8of32
R.D.Baldietal.:Theradio-loudAGNpopulationatz(cid:2)1intheCOSMOSfield
Table4.COSMOSSDSScolor.
Object u(cid:4) g(cid:4) r(cid:4) i(cid:4) z(cid:4) z
zphot,SDSS
22 <23.50 25.41±1.02 24.70±0.82 <23.00 <22.20
29 20.01±0.01 19.81±0.01 19.54±0.01 19.37±0.01 19.37±0.03 1.50+0.30
35 22.18±0.09 22.09±0.04 21.96±0.06 21.54±0.06 21.65±0.28 1.80−+00..5450
37 19.31±0.01 19.21±0.01 18.88±0.01 18.75±0.01 18.80±0.01 1.40−+00..4200
−0.40
COSMOS-FRI32 <23.50 <23.90 24.86±0.61 23.99±0.41 <22.20
COSMOS-FRI37 23.70±0.48 22.78±0.08 22.06±0.06 21.68±0.08 21.22±0.26
COSMOS-FRI226 24.41±0.65 <23.90 23.84±0.28 24.90±1.31 <22.20
COSMOS-FRI236 20.89±0.03 20.44±0.01 20.17±0.01 20.04±0.02 19.58±0.04 2.40+0.30
−0.35
Notes. SDSScolor, u(cid:4), g(cid:4),r(cid:4),i(cid:4),and z(cid:4), for the sources which show “power-low” SEDsand thephotometric redshifts, z , derived using
zphot,SDSS
SDSScolor(seeSect.6.1).
theχ2minimaisconsistentwiththespectroscopicredshifts.For atz∼1(e.g.,Huertas-Companyetal.2007).Wedonotseeany
object 35, the χ2 minimum indicates a redshift of 1.8, which evidentlate-typegalaxy,butgenerallywecantentativelyclassify
isdifferentfromthatwederivefromtheSED modeling(1.03). themasbulge-dominatedobjects.Onlyfoursources(namely18,
Wethenfinallychangetheclassificationofthissourcetoquasar 19,38and41)showmoreirregularmorphologiesthanclassical
becauseofitsSEDandopticalappearanceanduseasredshiftz= undisturbedellipticals(Fig.5),whichmightbepossiblesignof
1.80+0.40.Conversely,fortheobjects22and33andCOSMOS- aninteractionwithcompanion(s).Theopticalimagesofseveral
−0.40
FRI32,37,and226,theSDSScolorfittingdoesnotproducea objectsshowrichenvironmentsintheirsurroundings,similarly
reliableevidencefora redshiftwithinthe rangeofourinterest. towhatC09foundfortheCOSMOS-FRIsources.
Therefore,wefinallyexcludethesesixobjects(includingobject
10 thatis notdetectedin SDSS bands) fromthe entire sample,
6.3.Dustemission
sincetheirphotometricderivationisnotconvincing.
Summarizing,thesampleselectedinthisworkisreducedto Concerningthe43objectsselectedinthiswork,dustemissionis
43objectsaftertheSEDqualitytest,andwealsoexcludethree requiredto adequatelymodelthe SEDsof 16 objects(notcon-
sourcesfrom the sample studied by B13. Figure 3 summarizes sidering the three quasars) due to the detection of emission at
ourselectionprocedure,providingthenumberofthesourcesse- 24 μm, and significant excesses above the stellar emission are
lectedineachstepoftheselection. observed also at shorter infrared wavelengths in eight of these
galaxies.However,asdiscussedinSect.5,theresultsoftheSED
fitting, that concern the dust components should not be used
6.2.Hostgalaxyproperties
to infer dust properties. To explore the dust properties, we es-
We now focus on the properties of the host galaxies inferred timated the residualsbetween the best-fitting stellar modeland
fromtheSEDmodelingandinparticularontheirstellarpopula- thedata-points,lookingforanexcessattheSpitzerwavelengths.
tionsforthe43sourcesselectedinthiswork,similarlytowhat Wethenintegratedtheresiduals(byassumingthatthespectrum
donebyB13. isrepresentedbyamultiplestepfunction)toobtaintheinfrared
The stellar mass of the galaxy, M∗, is one of the most ro- excessluminosity,LIR excess intherangecoveredbytheSpitzer
bustresultsofthemodeling.However,asdiscussedinB13,the data,i.e.∼3−26μm(seeB13forthedetails).Theestimateddust
presenceofadditionaldustcomponentto the OSP mightaffect propertiesarereportedinTable3.
thestellarmassestimatemorethantheinclusionofaYSP.The Theanalysismissestheinformationonthedustcontentfor
inferredmassrangeis∼1010−1011.5 M(cid:3) (Fig.4),asreportedin thequasars,becausetheyhavebeentreateddifferentlyfromthe
Table3. restofthesample.WedonotmodeltheirSEDswithstellartem-
Although the other host parameters derived from the SED plates.Therefore,forthethreequasarsselectedinthiswork,we
modeling are less constrained than the estimate of the stellar estimatethedustluminositieswiththemethodmentionedabove
content in the galaxy, we can globally state that the hosts are and by assuming that the emission at the Spitzer wavelengths
dominatedbyanOSPwithanageof∼1−3×109years,whichis has only a dust origin. We also estimate the dust component
similartotheresultsobtainedbyB13.Assumingthattheemis- for the quasar selected by C09 (COSMOS-FR I 236) with the
sionatshortwavelengthsisassociatedwithaYSP,themostsig- samemethod.Table5showstheinferredIRluminositiesforthe
nificantUVcomponentarereproducedbystellarpopulationsof quasars.
afewMyr(Table3)withacontributiontothetotalmassofthe The dust luminosities of the sample selected in this work,
galaxylessthan1%. as expressed as infrared excess luminosities, are in the range
To qualitatively study the host type, the optical HST/ACS L ∼ 1043−1045.5 erg s−1, similar to that found for the
IR excess
images provides the highest resolution view of the galaxy, al- low-powerradiogalaxiesstudiedbyB13.TheFRIIscoverthe
though the maps are single orbit pointings. For the remaining entire range of IR excess luminosities, showing also nondetec-
(Subaru, CHFT, and Spitzer), optical and infrared images can tionsat24μm.
provideatentativeindicationofthehostmorphologyforallthe SimilarlytowhatisdonebyB13,wealsomeasuredthespec-
sources, apart from the four quasars, which show a point-like tralindexoftheinfraredresidualsoverthe OSPbetween8μm
opticalnucleusoutshiningtheweakergalaxy.With a visualin- and24μm,α .Consideringonlysignificant(>3σ)excessesat
IR
spection of the multiband counterparts of the host, we can at- 8μm,thisvaluecanbeestimatedineightcaseswithvaluesspan-
temptto recognizethe presence of clear spiral/disk galaxiesor ningbetweenα ∼ 1and−1.Fortheothereightobjectswitha
IR
galaxies,whichclearlydifferfromsmoothellipticalsasobserved 24μmdetection,theupperlimittothe8μmfluxtranslatesinto
A76,page9of32
A&A567,A76(2014)
Fig.2.Distributionoftheχ2 function(seetext)atvaryingredshiftforobjects22,29,35,and37andforCOSMOS-FRI32,37,226,and236as
obtainedfromthecolor-redshiftrelationusingSDSScolors(Richardsetal.2001b).
alowerlimitofα (cid:2) −1.Forthefourquasars(29,35,37,and
IR C09 sample
COSMOS-FRI236),wederivethespectralindexagainassum- 34
ing that the emission at 8 μm has only a dust origin (Tables 3 SED and
and5). sFoIuRrScTes r waditiho O pI t>ic 2a1l mag iSdeencutirfeic Hatoiostn photo−z quality
Since the temperaturesassociated with the thermal compo- F > 511 m5Jy 56 46 43 + 31
nent are poorly constrained, we prefer to crudely estimate the
Radio morphology
overalldusttemperaturefromthespectralindexαIR.Byassum- 38 compact The RL AGN
ilnatgeainstiongalteebmlapcekra-btuordeyradnugsetcoofm75p0o−ne1n2t0,0thKevaanldue3s50o−fα60IR0tKranfos-r 212212 FFFeRRxRtIIeIInded pin o pt h u e lf a7iCeti4lOodnS Mat Oz>S1
α = −1and1,respectively.Thederivedtemperaturedepends 1 FRI/FRII
IR
onredshiftwiththelower(upper)valuesofTbeingderivedfor Fig.3. Flow-chart describing our selection procedure. The number of
z=0.8(z=3). sourcesthatsurviveeachstepisreportedinsideeachcircle.Seetextfor
moredetails.
6.4.UVexcess
InspectionoftheSEDfitsthatareobtainedwith2SPDindicates emissionintheUVband.Aclear(marginal)UVexcessinseen
that the UV excesses (above the contribution of the OSP) are in18(12)sources,whichisproperlymarkedinTable3.There-
usuallypoorlyconstrained.Furthermore,the verystellar origin mainingSEDsdropsharplyintheUVandarewellreproduced
isnotgranted,andtheUVexcessmightbeduetoanAGNcon- bytheemissionfromtheOSPs.
tribution.Itisnecessarytointroduceamodel-independentcrite- ToquantifytheUVcontribution,fortheobjectsshowingan
rion to assess which sourcesreally show an UV excess, and to UV excess we measure the flux at2000 Å in the rest frame,
estimate its luminosity.We visuallycheckallSEDs andsearch L , from the best fitting model, similarly to what done by
UV
forsourceswithasubstantialflatteningintheSEDatshortwave- B13. For the UV-faint sources, we estimate an upper limit on
lengthsorwith achangeoftheslope betweentheOSPandthe the UV emission. For the four quasars, we measure the flux
A76,page10of32