CSIRO PUBLISHING PublicationsoftheAstronomicalSocietyofAustralia,2010,27,302–320 www.publish.csiro.au/journals/pasa The Southern 2MASSActive Galactic Nuclei Survey: Spectroscopic Follow-up with Six Degree Field FrankJ.MasciA,E,RocM.CutriA,PaulJ.FrancisB,BrantO.NelsonA,F, JohnP.HuchraC,D.HeathJonesD,MatthewCollessD, andWillSaundersD AInfraredProcessingandAnalysisCenter,Caltech100-22,Pasadena,CA91125,USA BAustralianNationalUniversity,ACT0200,Australia CHarvard-SmithsonianCenterforAstrophysics,Cambridge,MA02138,USA DAnglo-AustralianObservatory,POBox296,Epping,NSW1710,Australia ECorrespondingauthor.Email:fmasci@caltech.edu FPresentaddress:VermontAcademy,SaxtonsRiver,VT05154,USA Received2010January10,accepted2010May12 Abstract: TheTwoMicronAll-SkySurvey(2MASS)hasprovidedauniformphotometriccatalogtosearch forpreviouslyunknownredactivegalacticnuclei(AGN)andQuasi-StellarObjects(QSOs).Wehaveextended thesearchtothesouthernequatorialskybyobtainingspectrafor1182AGNcandidatesusingthesixdegree field(6dF)multifibrespectrographontheUKSchmidtTelescope.Thesewerescheduledasauxiliarytargets for the 6dF Galaxy Redshift Survey.The candidates were selected using a single color cut of J K >2 s − toKs!15.5andagalacticlatitudeof b >30◦.432spectrawereofsufficientqualitytoenableareliable | | classification.116sources( 27%)weresecurelyclassifiedastypeIAGN,20asprobabletypeIAGN,and ∼ 57asprobabletypeIIAGN.Mostofthemspantheredshiftrange0.0520%)thaninanyprevious(mostlyblue-selected)galaxysurvey.Asmallfraction ofthetypeIAGNcouldhavetheiropticalcolorsreddenedbyopticallythindustwithA <2magrelativeto V opticallyselectedQSOs.Ahandfulshowevidenceofexcessfar-infrared(IR)emission.Theequivalentwidth (EW)andcolordistributionsofthetypeIandIIAGNareconsistentwithAGNunifiedmodels.Inparticular,the EWofthe[Oiii]emissionlineweaklycorrelateswithoptical–near-IRcolorineachclassofAGN,suggesting anisotropicobscurationoftheAGNcontinuum.Overall,theopticalpropertiesofthe2MASSredAGNare notdramaticallydifferentfromthoseofoptically-selectedQSOs.Ournear-IRselectionappearstodetectthe mostnear-IRluminousQSOsinthelocaluniversetoz 0.6andprovidesincentivetoextendthesearchto ≃ deepernear-IRsurveys. Keywords: galaxies:active—quasars:general—infrared:general—surveys 1 Introduction 2002)hasemployedarangeofmulticoloropticalselection Muchofourknowledgeaboutthedistributionandprop- techniques with relaxed constraints on morphology to erties of active galactic nuclei (AGN) has come from searchforQSOstoredshiftsof 6.Thishasreducedthe ≃ samplesthatareflux-limitedatblueopticalwavelengths. biasrelativetothesimpleUV-excesscriteriausedinearly Thisisbecausetheirspectralenergydistributions(SEDs) surveys,buthasnoteliminatedit. generallyexhibitaUVfluxexcess.Suchsurveyscanbe AcompletecensusofAGNovercosmictimeisessen- veryefficientandcompletedowntotheirbluefluxlimit, tial for understanding galaxy formation and evolution e.g.,theLargeBrightQuasarSurvey(LBQS;Hewettetal. since the properties of the central black hole and host 1995).However,anysurveywithabluefluxlimitwillbe galaxy are intimately linked (see reviews in Ho 2004). relativelybiasedagainstobjectswhoseintrinsicemission ThefractionofAGNmissingfromopticallyselectedsam- peaksatotherwavelengths,e.g.,near-infrared(IR)emis- ples,bothasafunctionofredshiftandluminosity,isan sionfromthehostgalaxy(Mascietal.1998;Bennetal. importantparameter.Thisisexpectedtoberelatedtothe 1998). Alternatively, the optical/UV can be partially or dutycycleofblack-holefuelingandtimescalesforregu- heavily absorbed by dust, as revealed by radio, near-to- latingstarformation.Valuesarecurrentlyveryuncertain mid IR, and X-ray surveys (Webster et al. 1995; Gregg andrangefrom15%togreaterthan50%(e.g.,Richards et al. 2002; Polletta et al. 2007; Donley et al. 2008). etal.2003;Glikmanetal.2004,2007;Brownetal.2006). The Sloan Digital Sky Survey (SDSS; Richards et al. This uncertainty is due to: selection of the appropriate ©AstronomicalSocietyofAustralia2010 10.1071/AS10001 1323-3580/10/03302 http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 TheSouthern2MASSActiveGalacticNucleiSurvey 303 comparisonsampleofopticallyselectedAGN;properties (FIRST)radiocatalog(Greggetal.2002;Glikmanetal. ofthe‘unbiased’sampleandhowrepresentativeitis;and 2007).TheserevealedanumberofextremelyredQSOs difficulties in quantifying the amount of bias (e.g., dust athighredshift,someshowingstrongevidencefordust. extinction). Barkhouse & Hall (2001) studied the 2MASS colors of QSOsthatwereidentifiedatotherwavelengths,primar- 1.1 Near-IRSelection ily from the Veron-Cetty & Veron (2000) catalog, and Warrenetal.(2000)showedthatitispossibletoconstruct Georgakakisetal.(2009)usedmid-andfar-IRobserva- a complete K-band–limited QSO sample by combining tions of red 2MASS AGN to infer their relationship to opticalandnear-IRphotometry.Thisexploitsthecharac- luminousIRgalaxies(LIRGs).Mostofthesestudieshow- teristic K-band excess seen in QSOs compared to stars everusedsingleband2MASSdetections(inJ,H,orKs) and has been termed the KX-selection method.A num- andthereforecouldhavemissedmanyredAGN.Further- ber of small pilot surveys have employed KX-selection more,nonewereabletoprovideacensusofAGNinthe andvariantsthereof(e.g.,Croometal.2001;Sharpetal. 2MASScatalog. 2002; Jurek et al. 2008; Smail et al. 2008). The largest Auniformunbiasedsurveyof2MASSAGNwascar- isbeingcompiledfromtheUKIDSSLargeAreaSurvey riedoutbyFrancisetal.(2004)byselectingcandidates covering 12.8deg2 (Maddox et al. 2008). This survey in the southern hemisphere covering 12.56deg2 using a cliunrerdenAtlGyNr∼epwoirtthsaKsurfa1c7eadnednsziton1f.r2o.mThfiosrecgorloourncdutstsairgs-. 50%weremissed≤bySDSS,thereforerevealingalarge Spectroscopicfollow-uprevealedthat 1.2%werebroad- ∼populationofredQSOs. lineAGNand 4%weregalaxieswi∼thSeyfert2nuclei. ∼ AlthoughtheKXmethodisturningupmanyluminous Themainfindingswerethat:(i)thetypeIAGNarepre- redQSOstohighredshift,thesituationisdifferentforless dominately at low redshifts (z!0.3) and contamination luminouslocalAGN(e.g.,Seyfertnuclei).Theseareusu- from host-galaxy light would make them hard to find allynotfoundbycolorselectionsincehostgalaxylight inopticallyselectedQSOsamples(e.g.,theSDSS);and candominatetheirbroadbandcolors.Historically,theyare (ii)theincidenceoftypeIIAGNamongstlocalgalaxiesis foundbytakingopticalspectraofthenuclearregionsof higherthanusualwhencomparedtoblue-selectedgalaxy largesamplesofgalaxies(e.g.,Hoetal.1997).Manyof samples.Theresultsofthisstudyarecomplementaryto thesesamplesareflux-limitedatblueopticalwavelengths thosepresentedhereandwillbediscussedinmoredetail andhencesubjecttobias.Themostsignificantbiasisthat later. thebluelightisdominatedbyrecentstarformationwhich Theabovestudiesindicatethat2MASSissensitiveto overwhelmsanyemissionfromacentralAGN.Anear-IR thelocalAGNpopulation.Theluminosityofbroad-lined selected sample of local galaxies using color criteria QSOs,particularlyinthelocaluniverse,isonlyslightly analogous to that used in KX methods will reduce this greaterthanthatoftheirhostgalaxies(e.g.,Hao&Strauss bias. 2004).Onlyasmallamountofdustextinctionisneeded Thelargestnear-IRsurveytodateistheTwoMicronAll tomis-identifythemorturnthemintotypeIIAGN.This SkySurvey(2MASS;Skrutskieetal.2006).Therehave is in contrast to the heavily obscured, high-luminosity, been several studies that searched forAGN in 2MASS. and usually unresolved QSOs at high redshift. There- ThefirstwasthatfromCutrietal.(2002)inthenorthern fore,eventhoughnear-IRcolor-selectedsurveysareless equatorialsky.TheyselectedsourceswithJ K >2and biased than those in the optical/UV, they are still some- s K 15.51 at galactic latitude b >30 . S−pectroscopic whatbiasedagainstthereddestQSOs.Theydohowever s ◦ foll≤ow-up revealed that 75% w| e|re previously uniden- havetheadvantagethatcandidatesselectedinthenear-IR tifiedAGN, with 80%∼of these associated with broad will be bright enough to allow spectroscopic follow-up emission-line(type∼I)AGN—i.e.,Seyfert1sandQSOs— withrelativeease. and the remainder were narrow-line (type II) AGN — It is worth mentioning why a red J Ks color cut − typicallySeyfert2s,typeIIQSOsandliners.Theyspanned has proven so efficient at findingAGN in the relatively a redshift range of 0.032hasbeenshown magnitudecutwasinitiallyimposed.Ofmatches, 0.7% s − ≃ todiscriminateredAGNfromUV/optically-selectedones resulted in multiple (ambiguous) associations and were inlargesamplesofknownAGN(Barkhouse&Hall2001; excluded. This yielded 6386 matches with an overall Cutri et al. 2002). For example, 2MASS detects a large position-differencedispersionofσ 0.6arcsec.Asample ≃ fraction( 75%)oftheLBQSQSOsinallthreenear-IR of2260candidateswasthencompiledbyselectingsources ∼ bands (J, H, and K ). Most of these have J K <2. withSuperCOSMOSmagnitudesofb 18andr 17. s s J F − ≤ ≤ Therefore, J K >2 isolates the reddest subset of the Theselimitswererequiredtoobtaingoodsignal-to-noise s opticallysele−ctedpopulationandislikelytoprobemany ratiospectra(S/N"10pixel−1)andenablereliableiden- more.Itisalsointerestingtonotethatnearlyallknown tifications.ThereliabilityoftheSuperCOSMOSoptical QSOsatz!0.5haveJ Ks>1.2(Francisetal.2000; detections to these magnitude limits is expected to be − Barkhouse&Hall2001). >99.9%(Hamblyetal.2001b).Thesingleb andr band J F Inthispaper,weextendtheworkofCutrietal.(2002) photometryhasanaccuracyofσ 0.3magwhereas,due ∼ and Francis et al. (2004) to search for additional red to specifics of the calibration procedure, b r colors J F − 2MASSAGNinthesouthernequatorialsky.Weassem- are expected to have an accuracy of σ!0.12mag (for bledarelativelyunbiasedsampleofredAGNcandidates details, see Hambly et al. 2001b). The 2260 candidates using a color cut of J K >2 on the 2MASS Point were then proposed for follow-up with the 6dF multifi- s − SourceWorkingDatabaseandthenusedthebrute-force brespectrograph.1182wereeventuallyallocatedfibers, capabilitiesofthesixdegreefield(6dF)multiobjectspec- mainlyassecondarytargetsduringschedulingofobser- trograph to obtain spectra of a subsample. We utlized vations for the 6dFGS (Jones et al. 2004). Our objects theefficientmappingstrategyofthe6dFGalaxySurvey weredistributedoveraneffectivenon-contiguousareaof (6dFGS)withourcandidatesselectedassecondarytargets 1592deg2. ∼ intheprogram. Itisimportanttonotethatourinitialsampleofcandi- OursampleandtargetselectionaredescribedinSec- dates(withJ K >2)wasselectedfromanearlyversion s − tion2.Observationsanddatareductionaredescribedin of the 2MASS Point Source Working Database. Subse- Section3,andspectralclassificationsinSection4.Prop- quentrecalibrationandselectionofalternateobservations ertiesofthenewlydiscoveredAGNandcomparisonsto ofsomeofthesesourcesforinclusioninthefinal2MASS opticallyselectedQSOsamplesarediscussedinSection5. PSCresultedinsomeofthemhavingcolorsJ K <2. s − ConclusionsaregiveninSection6.Weassumeaconcor- In the end, the majority of sources classified as AGN dancecosmologywithH0 70kms−1Mpc−1,"m 0.3, hadJ Ks"1.5,with 20%satisfying1.5 J Ks 2 = = − ∼ ≤ − ≤ and" 0.7.Allmagnitudes,unlessotherwisespecified, accordingtophotometryinthepublic-releasePSC.Uncer- # = arebasedontheVegasystem. tainties in the J Ks colors were typically !0.16mag − (1-σ). 2 SampleandTargetSelection 3 ObservationsandReduction Candidateswereinitiallyselectedfromthe2MASSPoint SourceWorkingDatabaseusingthefollowingcriteria:a Spectrawereobtainedoverthecourseofthe6dFGSdur- colorcutofJ K >2;K 15.5;detectionsinallthree ing2001–2006usingtheUKSchmidtTelescopeandthe s s − ≤ bands (J, H, and K ); galactic latitude b >30 ; and 6dF spectrograph (Watson et al. 1998; Saunders et al. s ◦ excludingaregionof 170deg2 covering|th|eLargeand 2001). Fordetailsonthe6dFGSobservingstrategy,see ∼ Small Magellanic Clouds. Previously identified sources Jones et al. (2004, 2009). The primary sample for the were not omitted. This yielded 16977 candidates in an 6dFGS was drawn from the 2MASS Extended Source effectiveareaof 20400deg2overthewholesky.These Catalog(XSC;Jarrettetal.2000).Seventeenadditional ∼ criteriadefinethe‘master’catalogofredAGNcandidates, (secondary)extragalacticsamplesweremergedwiththe andwereusedinnorthernhemispherefollow-upstudies primary sample (see table 3 in Jones et al. 2009). Dur- byCutrietal.(2002). ingsurveydesign,theseweregivenpriorityindicesand NotethatadetectionintheH-bandwasincludedfor our initial sample of 2260 candidates had a complete- reliability.TheredAGNcandidateselectioncriteriawere nessincoverageof91.7%.Thisgave 6AGNcandidates ∼ originally devised during the early stages of the survey per 6dF on average, although not all 6dFGS fields con- before many of the source quality metrics were mature. tainedourtargetsbecauseofthedifferentgalacticlatitude Sources detected in all three survey bands were known constraints. to be the most reliable. Therefore, three-band detection The 6dF multifiber spectrograph was able to record wasincludedwiththetwo-bandcolorlimittominimize up to 120 simultaneous spectra over a 5.7 field. Each ◦ sample contamination by spurious sources with unusual fiber has a projected diameter of 6.7arcsec on the sky. colors. The2MASSpositionswereaccurateto 0.5arcsecand ≤ Southernequatorial(δ< 0 )AGNcandidatesfromthe therefore light losses due to fiber positioning errors ◦ mastercatalogwerepositionmatchedagainsttheSuper- wereexpectedtobesmall.Forthe10th–90thpercentile COSMOS Sky Survey database (Hambly et al. 2001a). range in redshift for the extragalactic identifications, A match radius of 4arcsec was used and no optical z 0.15–0.45,thefiberdiametercorrespondstophysical ≃ http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 TheSouthern2MASSActiveGalacticNucleiSurvey 305 scales of R≃17.5 to 38.7kpc h−701. This means the 6dF spectra sampled light from entire galaxies, and not necessarilytheirnuclei. Each spectrum was taken using V and R gratings, whose outputs were later spliced to cover the effective wavelengthrange: 3900–7500Å.TheobservedS/Nwas typically 3–10pixe∼l 1, with >10pixel 1 being nominal − − due to the brightness of our sources. Spectra with low S/Nwereprimarilyduetopoorobservingconditions.The spectral resolution was typically R 1000 throughout, ∼ corresponding to emission-line full width at half max- ima (FWHM) of 4–8Å over the observed wavelength ∼ range.Thisenabledustoresolverest-framevelocitiesof "205kms−1overtherangez 0.15–0.45,sufficientfor ≃ AGNidentificationandclassification. The data were reduced, spectra extracted, and wavelength calibrated using a modified version of the Two degreeFieldDataReduction(2dFDR)packagedeveloped forthe2dFGalaxyRedshiftSurvey.Detailsofthereduc- tionaredescribedinJonesetal.(2004)andproductsfrom thefinaldatarelease(DR3;2009April)aredescribedin Jones et al. (2009).The flux calibration was very crude Figure1 KsbrightessdistributionofproposedAGNcandidates, sourceswithobservedspectra,andsourcesforwhichwesecured inthatthesameaveragespectraltransferfunction(derived a reliable spectral identification. The top horizontal axis shows onceusingacoupleofstandards)wasassumedforevery theapproximatecompleteness( numberspectraobserved/number = 6dF observation for all time. The spectra are therefore candidates)forseveralmagnitudebins. not of spectrophotometric quality. This severely limited ourclassificationprocess,e.g.,usingemissionlineratios (see Section 4). The spectra were corrected for atmo- spheric absorption and emission features. However in somecases,imperfectsky-subtractionhaslefttheimprint ofthebrightestskylines. Quality flags were assigned by the semi-automated 6dFGSredshiftdeterminationpipeline(seeSection4for details).Almost all redshifts were visually inspected by the6dFGSteam.QualityflagsintherangeQ 1–4were assignedinthefinalpubliccatalog2.Q 4r=epresentsa = very reliable redshift where, typically, the median spec- tralS/Nwas 10pixel 1.Q 3wasassignedto‘likely’ − ∼ = redshiftandQ 2to‘tentative’redshiftwithspectrawar- = ranting further examination. We visually examined all spectra with quality flags Q 2, although the majority ≥ of usuable spectra had Q 4 and a handful had Q 3. = = Duetothefaintnessofthesourcesingeneral,750ofthe 1182spectraobservedwereofsuchpoorqualitythatno classificationwaspossible.Classificationsweretherefore Figure2 J Kscolordistributionofsourceswithobservedspec- − securedfor432spectra. tra,sourcesforwhichwesecuredareliablespectralidentification, andthoseidentifiedastypeIandtypeIIAGN. Figure 1 shows: the number of proposed AGN candidates (using the optical/near-IR constraints defined in Section2);thenumberof6dFspectraobserved;andthe seenintheCutrietal.(2002)sampleof704candidates numberwithsecurespectralidentificationsasafunction withfollow-upopticalspectroscopy.Figure2showsthat ofK magnitude.Thedearthofcandidatesinthefaintest wearenotsignificantlybiasedagainstidentifyingsources s bin,152cutoff.This tification rate as a function of J K is approximately s s − − cutoffimpliesJ"17forKs>15andhenceafractionof uniform. sources are expected to fall below the J-band flux limit Figure1showsthatthenumberofspectraobserveduni- andbeexcludedfromthecandidatelist.Thisdropwasalso formallysamplestheK distributionofcandidates,i.e.,the s completenessisapproximatelyuniform.However,thereis 2Accessedviahttp://www.aao.gov.au/6dFGS/. relativelyhigherincompletenessinthenumberofspectra http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 306 F.J.Mascietal. Table 1. Rest wavelength regions used in emission-line measurements Line Centera Continuumintegration Lineintegration (Å) limits(Å) limits(Å) [Ciii] 1908.73 1800–1850,1970–2010 1860–1955 Mgii 2798.75 2650–2700,3000–3050 2750–2850 [Oii] 3728.48 3650–3700,3770–3815 3710–3740 Hβ 4862.68 4740–4840,4880–4940 4845–4880 [Oiii] 5008.24 4880–4940,5030–5100 4990–5025 Hα 6564.61 6400–6520,6630–6700 6550–6572 [Nii] 6585.28 6400–6520,6630–6700 6572–6594 [Sii] 6725.48b 6630–6700,6745–6845 6700–6745 aAsdefinedinVandenBerketal.(2001). bAverageofdoublet[Sii]λλ6718.29,6732.67. 432spectrawereofsufficientqualitytoenableaclassi- Figure3 bJ Kscolordistributionofsourceswithobservedspec- ficationofsomesort,butnotnecessarilyanunambiguous tra,sourcesfo−rwhichwesecuredareliablespectralidentification, identification.Allspectrawereshiftedtotheirrestframe andthoseidentifiedastypeIandtypeIIAGN. usingredshiftsdeterminedbythe6dFGSprogram. 4.1 Emission-LineDiagnostics identified at the faintest magnitudes, 14.514.5)sourcestotheoriginalcan- continuum level. Dispersion velocities were determined s didate K distribution (from Cutri et al. 2002) with no fromtheFWHMofthelines.Thelinesofinterestandthe s optical magnitude limit imposed, we estimate we have effectivewavelengthregionsusedtodefinethecontinuum lost"35%ofcandidatesduetothisopticalcut.Amajority andlineintegrationlimitsareshowninTable1. ofthesemissedcandidates(withb >18)haveb K ThefitprofstaskinIRAFwasusedfortheautomated J J s colors 4–6. However, the spectrally-observed b −K measurementoflinediagnostics.Thisincludedtheabil- J s distribu≃tion(Figure3)showsthatwearenotcompl−etely itytodeblendcloselyseparatedlines,e.g.,Hαand[Nii]. biasedagainstidentifyingthereddestsources.Whencom- An important input parameter for the fitprofs task is an paredtothecolorsofopticallyselectedQSOs,the2MASS estimate of the 1-σ uncertainty per pixel. This allows AGNhaveatailextendingtomoderatelyreddercolors(see the program to compute uncertainties in each of the fit- Figure10andSection5.2formoredetails). tedlineparameters.Sincethefittingwasnon-linear,this was accomplished using a Monte Carlo simulation.The spectraluncertaintywascomputedbyfirstselectingarel- 4 Classification atively clean region in the rest frame common to each All spectra were initially classified using the semi- spectrum,i.e.,devoidofstrongemissionandabsorption automated6dFGSclassificationsoftware,whoseprimary lines.Weselectedtherestwavelengthrange5050–5400Å. purposewastodetermineaccurateredshifts.Thisisamod- Wethenfittedastraightlinetothedatainthisregionusing ifiedversionoftherunzsoftwareusedforthe2dFGalaxy arobust(outlier-resistant)regressionmethodbasedonthe RedshiftSurvey(Collessetal.2001).Itused13spectral conceptof‘M-estimation’(Huber1981).Theuncertainty templatestoidentifyspectrausingline-fittingandcross- was then estimated using the median absolute deviation correlationtechniques.Ingeneral,thisprogramproduced in the residuals from the fit, and is also robust against veryreliableredshiftsforallgalaxies,althoughwasless potentialoutliers: reliable at separating out the variousAGN classes from late-andearly-typegalaxies,andstars.Allspectrawere σ 1.4826median p fit p , (1) i i ≃ {| − { }|} visually inspected to determine whether a poor-quality spectrumflaggedbythe6dFGSsoftwarewasworthyof where p is the value of the ith pixel in the 1-D spec- i furtherexamination. trumandfit p isthefittedvalue.Thisquantityisscaled i { } http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 TheSouthern2MASSActiveGalacticNucleiSurvey 307 Figure4 Distributionofrest-frameHαandHβequivalentwidths Figure5 LineratiodiagramforgalaxieswithtypeIAGNclassifi- forallgalaxieswiththebestqualityspecta.Wearesensitivetoall cationsremoved.Diamondsandfilledcirclesare‘probable’typeII equivalentwidthstotherightoftheverticaldottedline(>5Å). AGNandstar-forminggalaxies,respectively,allat 0.2dex(1-σ) ≥ fromtheclassificationboundaryofKewleyetal.(2001,solidline). Crossesarecomposites(classifiedasunknowngalaxies).Errorsin suchthatitconvergestothestandard-deviationofaGaus- thelineratiosaretypically0.2dex(1-σ). sian in the limit of a large sample. For spectra where therange5050–5400Åincludedorfelloutsidethelong wavelength end (λ ) after shifting to the rest frame, AGN; type II AGN; starburst or late-type star-forming red a wavelength range of λ 250 λ λ 20Å was galaxies; early-type galaxies; stars; and unknown emis- red red − ≤ ≤ − usedinstead.Inallcases,thisensured>20pixelsforthe sionlinegalaxies.Theseclassesandthecriteriausedto noisecomputation. identifythemareasfollows. WeestimatedthesmallestEWwearesensitivetoby Spectra with broad Hα and/or Hβ emission lines examining the dispersion in Hα and Hβ EWs of all the exceeding 1000kms 1 (FWHM), or with other broad − galaxies(andpotentialAGN)withthebestqualityspectra permitted lines present, e.g., [Ciii] or Mgii for z"1 (Q 4).Figure4showsthesedistributions.EWmeasure- andz"0.4,respectively,wereclassifiedastypeIAGN. = mentsclusteredaroundzeroarelinelessgalaxieswherean Included in this criterion are S/N 2.5 on the FWHM ≥ identificationwouldbehighlyunreliable,ifatallpossible. measurementandaHαorHβEW>5Å.Spectrainwhich We found we should be sensitive to galaxies with rest- knownbroadlinescouldbediscernedbyeyebutwererel- frameEWineitherHαorHβof"5Å.Givenourobserved ativelynoisy,i.e.,withfluxS/N<2.5wereclassfiedas wavelengthrange,eitheroftheselinesareexpectedtobe ‘probable’typeIAGN. observedatz!0.5andthereforewereusedasconstraints Non-type I AGN spectra were classified using line intheidentificationprocessbelow. ratios involving good measurements in either of the LinefluxesandEWswerealsomeasuredinteractively followinglinepairs:([Oiii],Hβ)or([Nii],Hα)or([Sii], byintegratingthelinefluxesdirectlyfromthe1-Dspectra. Hα)or([Oiii],[Oii]).Wefirstattemptedaclassification These were in excellent agreement, to within measure- using the diagnostic diagrams of Kewley et al. (2001, ment error, with the profile-derived fluxes from above. 2006), which are based on the classic BPT diagrams of Alllineswerevisuallyinspectedandunreliablefluxmea- Baldwin et al. (1981). Figures 5 and 6 show the tradi- surementsflagged.Thesewereprimarilylinesthatwere tionalline-ratiodiagramsusingourgoodqualityspectra contaminatedbyastrongskylineoratmosphericabsorp- (withpre-classifiedtypeIAGNremoved)andwhereall tionband.Ourfinalemissionlinedatabaseretainedlines fourlineshadfluxS/N 2.5.Unfortunately,allfourlines ≥ with fluxes "2.5σ, and lines that were clearly discern- ineitherFigure5or6wereonlysimultaneouslyvisible ablebyeyeincaseourautomatedmeasurementofσwas (andwithgoodS/N)in 8%(23/296)ofthegood-quality ≃ overestimated. Unreliable σ estimates occured in 7% non-type I spectra. Furthermore, the errors in the line ≃ ofthespectra.Notethatwedidnotcorrecttheemission ratios( 0.2dex,1-σ)weretoolargeforthebulkofthese ≃ linefluxesforanyunderlyingabsorption(e.g.,fromstellar spectratobereliablyclassified.Wethereforedeclaredthe photospheres)sinceastudyusingsimilarspectrafrom2dF fewtypeIIAGNandstar-forminggalaxiesthatcouldbe byFrancisetal.(2004)foundthiseffecttobenegligible. classifiedusingthismethod(atdistances 1-σ fromthe ≥ A first pass examination of the spectra together with classificationboundaries)tobeprobableidentifications. initial classifications provided by the 6dFGS program For the remaining 273 sources with good qual- motivated us to define six broad object classes: type I ity data, and where only one of the above line pairs http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 308 F.J.Mascietal. Earlytypegalaxieswereidentifiedthroughthecharac- teristic 4000Å break, a signature caused by the dearth of hot and young (usually O- and B-type) stars and strong heavy-metal absorption by stellar photospheres. Starswereisolatedbyfirstensuringthattheirradialveloc- itieswere!150kms−1.Theirspectrawerethenmatched totemplatesfromtheELODIEstellarlibrary(Moultaka etal.2004).ThemajoritywereKandMdwarfstars.All othergalaxy-likespectrawithHαorHβEW>5Åbutnot fittingtheabovecriteria—e.g.,withsinglelinemeasure- ments,orcompositeslyingwithin1-σ ( 0.2dex)ofthe ± type II/starburst classification boundaries in Figure 5 or 6—wereclassifiedas‘unknowngalaxies’. 4.2 ResultsSummary Table 2 summarizes our source classifications.We only includeoursecureidentificationsforthetypeIAGN,and probable identifications (as described in Section 3) are Figure6 LineratiodiagramforgalaxieswithtypeIAGNclassifi- classedas‘unknowngalaxies’.Alsoincludedarestatistics cationsremoved,butwith[Sii]intheabscissa.Diamondsandfilled for type I and type IIAGN from the Cutri et al. (2002) circlesare‘probable’typeIIAGNandstar-forminggalaxies,respec- northern 2MASSAGN survey and Francis et al. (2004) tively.ThesolidlineistheAGN/star-formationdiscriminatorfrom Kewleyetal.(2001).Crossesarecomposites(classifiedasunknown southern 2MASSAGN survey.The latter is broken into galaxies).Errorsinthelineratiosaretypically0.2dex(1-σ). twocolorcuts.TheCutrietal.(2002)studyhasatleast twicethedetectionratefortypeIAGN.Thiscouldbedue was available (predominately when z"0.1), a galaxy todeeperspectroscopicfollow-upoffaintersingletargets was classified as a ‘probable’ type II AGN if either intheirstudy.Itispossiblethatasignificantfractionofour of the following was satisfied: log([Oiii]/Hβ)>0.3 faintertargetsatK >14.5(e.g.,Figure1)couldnotbe s or log([Nii]/Hα)> 0.2 or log([Sii]/Hα)> 0.35 (e.g., securedaretypeIAGNthroughspectralidentification.Itis − − Zakamska et al. 2003) or log([Oiii]/[Oii])>0 (e.g., alsointerestingtonoteinTable2thatthereisatendency Fraquelli & Storchi-Bergmann 2004; Kewley et al. for the type I AGN identification rate to increase with 2006). Combined with any of these, we also required J K color. s a rest-frame FWHM([Oiii])>300kms 1, FWHM(Hα −Figure 7 shows a sampling of spectra for the new − or Hβ)<1000kms 1, and Hα or Hβ EW>5Å. The type IAGN, primarily those with the highest redshifts. − FWHM([Oiii])limitwasincludedtoimprovetherelability Two of the sources are at z>1: 2MASS J21571362- oftypeIIidentificationswhenonlyonelinepairwasavail- 4201497withz 1.321and2MASSJ10012986-0338334 = able. For comparison, Zakamska et al. (2003) assumed withz 1.389.Thelatterhasbeenclassifiedasaprobable FWHM([Oiii])>400kms 1. We assumed 300kms 1 typeIA=GNduetoalowspectralS/N,althoughgivenits − − since the distribution for FWHM([Oiii]) for their entire relativelyhighredshift,itismostlikelyaQSO. typeIIsamplefallsoffsharplyat<300kms 1.Intheend, Table3liststhesecure(T1)andprobable(PT1)typeI − thislimitmadelittledifferencetothetypeIIidentification AGN identifications.There are 116 classified asT1 and statistics. 20 as PT1. Previous or alternative names as listed in Probablestarburst/late-typestarforminggalaxieswere the NASA Extragalactic Database (NED) are given. Of classified using the negation of these single line ratios the136typeIAGN,8( 6%)werepreviouslyclassified ∼ with some buffer to allow for flux errors, i.e., those as either ‘AGN’, ‘QSO’or ‘AGN/QSO?’in NED. Four with: log([Oiii]/Hβ)<0.2, or log([Nii]/Hα)< 0.3, or of these are in the SDSS QSO sample. This implies a − log([Sii]/Hα)< 0.4,orlog([Oiii]/[Oii])< 0.2. majorityarenew,previouslyundiscoveredAGN.Interest- − − ItisimportanttonotethatthetypeIIAGNidentified ingly,tenofourtypeIAGNwerepreviouslydetectedin usingtheabovesinglelinepairscouldbecontaminatedby X-ray by the ROSAT All-Sky Survey (RASS). Table 4 low-metallicityemission-linegalaxiesorliners,especially liststhetypeIIAGN,allofwhichareclassifiedasprob- atlowredshift.Furthermore,thenon-spectrophotometric able using the methods described in Section 3. None of natureofourspectracouldinvalidatesomeidentifications thetypeIIAGNwerepreviouslyclassifiedasAGN-like, made using widely separated lines (e.g., the pair [Oiii], and only one was detected in X-ray by the RASS. Of [Oii]). These classifications are therefore very tentative the previous classifications available in NED, a major- giventhequalityofourdata.Hence,wedeclarealltype ityofourtypeIandIIAGNarelistedasgalaxy-likeand IIAGN identifications quoted in this paper to be prob- extendedintheoptical(SuperCOSMOSdigitizedplates) able. Follow-up with higher S/N spectral observations, ornear-IR(2MASSAtlasImages).Atleast30%arealsoin preferablywithbettercalibratedthroughputasafunction the2MASSExtendedSourceCatalog(XSC;Jarrettetal. ofwavelength,willbeneededforconfirmation. 2000).Thisisexpectedgiventhedepthofoursample. http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 TheSouthern2MASSActiveGalacticNucleiSurvey 309 Table2. Sourceclassificationsandcomparisonstopreviousstudies Thisstudy Cutrietal.(2002) Francisetal.(2004) Francisetal.(2004) (J Ks!1.7) (J Ks>2.0) (J Ks>1.2) (J Ks>1.8) − − − − Numberclassified 432 664 1304 66 Stars(%) 23(5.3)a 66(9.9) 330(25.3) 6(9.1) Unknowngalaxies(%) 193(44.7) … … … Early-typegalaxies(%) 17(3.9) … … … SB/late-typegalaxies(%) 26c(6.0) … 106(8.1) … TypeIAGN(%) 116b(26.8) 385(57.9) 14(1.1) 4(6.0) TypeIIAGN(%) 57c(13.2) 100(15.0) 23(1.8) 0(0.0) aValuesinparenthesisarepercentagesofthe‘numberclassified’(firstrow). bThe20probableidentificationsareexcludedhereandclassifiedas‘unknowngalaxies’. cWedeclareallthesetobeprobableidentifications. Figure7 Rest-framespectraofsomenewtypeIAGNoverlayedwithemissionlinestypicallyfoundinQSOspectra.Thespectraforall objectslistedinTables3and4canbeviewedbyqueryingthe6dFpublicdatabase:http://www.aao.gov.au/6dFGS/. 5 Discussion AGNareatlowredshifts,withonlytwoatz>0.7.There are six securely identified AGN (four type I, two type This section reviews the properties of our 2MASS II) at z<0.05.This is 24% (6/25) of all secure galaxy- AGN and compares them to those of AGN/QSOs dis- like spectral identifications (including unknown types) covered in optical surveys. We explore their redshift, in this redshift range. This is a lower limit since some luminosity, photometric and line EW distributions. Our objects classified as ‘unknown’ could be type II AGN. primarybenchmarkandcomparisonsampleofoptically- Even removing our ‘probable’ type II AGN, the AGN selected AGN/QSOs is the SDSS Quasar Catalog Data fraction is still relatively high. For comparison, Hao & Release 5 (DR5; Schneider et al. 2007). This cata- Strauss (2004) find 4% of 15200 SDSS-detected log contains 2MASS matches to 9824AGN, all within ∼ ≃ galaxiesatz<0.05harborAGN(mostlySeyferts).Anear- 2arcsec. lierstudybyHuchra&Burg(1992)foundAGN(including LINERs) in 3.4% of a sample of 2399 nearby blue- 5.1 RedshiftandLuminosityDistributions ≃ selectedgalaxies.Thesestudiesarenotafaircomparison Our 2MASS AGN span the range 0.01!z!1.38 as sincethegalaxieswereopticallyselected.Itwouldbeof shown in Figure 8a. The median z is 0.27 and 0.21 interesttodeterminethefractionofSDSSgalaxieswith ≃ ≃ fortypeIandtypeIIAGN,respectively.Amajorityofour activenucleiforacolorcutofJ K >2. s − http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 310 F.J.Mascietal. 3 4 0 0. 1. 8. Othername 2MASXJ00004028-0541012 IRASF00063-62492MASXJ00114350-50333021RXSJ001633.2-054227 2dFGRSS440Z049IRAS00444-1803 1RXSJ005932.7-154032 APMUKSB012644.60-24120SUMSSJ013401-5618442MASXJ01354638-3539151SDSSJ013809.53-010920.2 SDSSJ015530.02-085704.0 APMUKSB015713.48-20253 2MASXJ02155306-4709573 2dFGRSS463Z081 SDSSJ023918.70-011521.0APMUKSB024304.02-16361IRASF02437-1145 2MASXJ02574849-0918440NVSSJ025938-151306 bD 111111111111111T11T111111T1T11T11T11111111T11111T1111 I TTTTTTTTTTTTTTTPTPTTTTTPPTPTPTTTTTTTPTTTTPTTT edshift 0.0940.3890.1840.1400.2370.3630.3190.4350.1860.1470.2070.2700.2540.2050.3850.4620.0200.3280.1370.2730.3680.1640.1610.3170.4260.4380.3050.1400.5680.0950.0090.4370.3190.2490.2930.2490.3370.3120.3740.2860.2700.4600.4730.1450.354 R Ks 292139627292068330016227536565986508505407402 195118289516246395073766461833065880367373342 −292118009721678470020002019000101920099048011 J 2.1.2.2.2.1.2.2.1.2.2.2.1.1.1.2.1.2.2.2.2.2.2.2.2.2.1.2.2.2.2.2.2.1.2.2.2.1.1.2.2.2.2.2.2. 595591043081863832618068622246564981929249696 102295290059708256945977181052327124541538210 N K 398129003546786407318660814606405199039221939 G 3.4.1.3.3.4.5.4.4.2.4.4.4.4.4.4.5.3.3.3.3.2.3.4.4.4.4.2.5.2.4.5.3.4.3.2.5.4.4.4.3.4.4.3.3. A 111111111111111111111111111111111111111111111 I e p y T 000000000000000000000000000000000000000000000 ble3. rF 16.7518.1916.5316.8017.0717.6817.7217.1917.5917.0817.7817.5516.8017.9717.3217.9117.7717.1917.0516.3617.2516.9117.2717.6718.0017.7217.8716.6918.1715.5417.3917.9316.3817.5316.9415.4118.0617.6218.1517.6616.3417.9717.1117.0216.76 a T 427917667463313886384555206461133278922197776 bJ 7.88.57.28.07.67.99.37.48.78.88.58.58.38.77.88.59.47.48.06.68.07.98.19.18.49.28.97.67.86.67.88.67.18.47.45.68.67.48.58.86.38.87.28.07.1 111111111111111111111111111111111111111111111 953042732036780825314054888111841742131369462 0.0.5.0.1.8.3.8.1.2.7.4.9.3.7.5.0.5.5.0.2.4.8.8.0.3.3.7.9.9.2.5.5.4.9.1.4.6.1.3.6.3.8.4.9. ac. 102531332345920413706190026131836384919245708505001593952423159414042083654452342382148430 e 423345502402435551302521403013420250051235311 D 572052102743514336511810628703446253551615295 046500033113154225300012006415210302150114101 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− 620406688523165640547390271414414243539613255 233514105010149927355062242064800519536806743 aA. 40.07.52.43.33.26.51.50.57.00.38.52.32.42.45.33.07.01.46.09.23.30.30.35.28.01.40.53.14.19.22.48.50.06.35.37.13.52.18.24.08.58.41.48.38. 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SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS me ASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASASAS a MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM N 222222222222222222222222222222222222222222222 http://journals.cambridge.org Downloaded: 16 Jun 2014 IP address: 134.4.141.201 TheSouthern2MASSActiveGalacticNucleiSurvey 311 7 ) ASXJ03103473-6412054 SSJ033609.54-061913.1 SSJ034134.07-054715.7ASXJ03440465-1252222XSJ035616.4-123712ASXJ03561995-6251391SSJ040234-315301 ASXJ04225654-1854424 GAJ0433.3-1422 SSJ043647-112347 ASXJ04481922-2158468 MUKSB050450.33-342037.GAJ0522.3-4524 RSB120745.5-114029 ASXJ12154013-2350126 ASXJ13500249-2619306 Continued( M D DMRMV M W V M PW C M M 2 S S212N 2 1 N 2 A1 L 2 2 1 1 1 1 1 1 11111T1111111T11111111111111111T1T11111T11T1111 TTTTTPTTTTTTTPTTTTTTTTTTTTTTTTTPTPTTTTTPTTPTTTT 40240183373887304267817271503229412168202713685 39559837839109236414990151597738509309339032709 31322242310312630523002341131133231424242553222 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0. 07102920770585649936159199300238756113127474061 16493367903548010037332440909123086215062714505 19022162902990022012021202929100000710093091902 2.1.2.2.2.2.1.2.1.2.2.1.2.2.2.2.2.2.2.2.2.2.2.2.2.2.1.2.1.2.2.2.2.2.2.1.2.2.2.1.2.2.1.2.1.2.2. 02038210451873555102820638781670934848580642334 53896886590216240209292050161918360645179857836 12565516550869576605847754472252516056020778712 4.3.2.4.4.4.5.3.3.4.3.4.2.3.4.4.1.4.4.3.3.4.3.4.4.3.4.3.4.3.4.4.4.4.4.5.3.4.4.5.4.4.4.3.4.4.4. 11111111111111111111111111111111111111111111111 00000000000000000000000000000000000000000000000 45443621370573681590137370568909345253258628410 97485749317520854368387494974330930794430538604 6.6.5.7.7.7.8.6.6.7.6.7.7.7.7.7.4.7.7.6.6.7.6.7.7.7.7.6.7.7.7.7.6.7.8.7.6.7.7.8.8.7.7.7.7.7.7. 11111111111111111111111111111111111111111111111 06913191973066539482058347416325957506956894261 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The Southern 2MASS AGN Survey: spectroscopic follow-up with 6dF

Similar The Southern 2MASS AGN Survey: spectroscopic follow-up with 6dF