1992ApJ. . .393. . .90H al. 1978),aswellsimpleincompleteness (Huchra,Wyatt,& uum (Salzer1989),andredshift (theIIIa-Jeffect—Bohuskiet with color(UVexcess),contrast ofemissionlinestothecontin- references therein).Theseare known tohavebiasesassociated vetskii 1976,andreferencestherein; MacAlpineetal.1978,and etc.). Alloftheopticalanalysessufferfrommajorselection objective-prism surveys(Markarian 1967;Markarian&Lipo- the majorityofthesestudies dependonsamplesfrom effects thatcanseriouslylimittheirusefulness.Forexample, luminosity function(Tananbaumetal.1978;Elvis ewski 1983;Weedman1977;Bohuski,Fairall,& ian 1974,1977;Terebizh1980;Meurs&Wilson1984;Wasil- Reichert &Shafer1984;Maccacaro,Gioia,Stocke1984, possible tracersofgalaxydistributions). their contributionstotheX-raybackgroundanduseas optical luminosityfunctionofSeyfertgalaxiesalone(Sargent but alsotheirevolutionandpositionincosmology(e.g., are ofinterestnotonlytounderstandtheoriginsuchobjects relative fractionoffieldgalaxiesthatareAGNs.Theseresults absolute volumedensityofcommontypesAGNsandthe 1985; Marshall1985,1987,etc.)andseveralontheirX-ray 1978; Veron1979;Osterbrock&Dahari1983;Chenget al. 1972; Huchra&Sargent1973;NotniRichterArakel- (AGNs) hasbecomeoneofthemostpopularfieldsin the fieldisstillplaguedbymanymisconceptions. tion to“normal”galaxiesarestillunanswered.Evenworse, origin, centralenergygenerationmechanismsandtheirrela- these objects,manyfundamentalquestionsconcerningtheir astronomy. Despitethenumberofpublicationsdealingwith The AstrophysicalJournal,393:90-97,1992July1 © 1992.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. To date,overadozenpapershavebeenwrittenonthe The particularproblemwewilladdressinthispaperisthe Over thelasttwodecadesresearchonactivegalacticnuclei -1 -1 Subject headings:galaxies:active—Seyfert galaxies. LINERs, butfindsevereselectioneffectsinouropticallyselectedsampleofsuchobjects. density ofSeyfert2galaxiesisfoundtobeapproximatelytwiceaslargethespace1 axies intheCfAsurvey(2399galaxiestotal)moreluminousthanM=—21.5areAGNs(H100kms of galaxiesthatareactivegalacticnuclei(AGNs)risessteeplywithabsolutemagnitude.Threethefivegal- stantial agreementwithourpreviousestimatesbasedonconsiderablymoreincompletesamples.Thefraction Mpc); thetwomostluminousgalaxiesinCfAsurveyarebothSeyfert1galaxies.Theintegratedspace and magnitudelimitoftheCfARedshiftSurvey.ThespatialdensitySeyfertgalaxiesiscalculated;classical Seyfert galaxiescomprise1.3%ofallatintegratedabsolutemagnitude—20.0.Thisresultisinsub- B0 © American Astronomical Society • Provided by the NASA Astrophysics Data System We alsoattempttomeasurethespatialdensityofothertypes“active”galacticnuclei—inparticular We defineandusea“complete”sampleof25Seyfert1232galaxieswithinthespatialbounds THE SPATIALDISTRIBUTIONOFACTIVEGALACTICNUCLEI.I.DENSITY 1. INTRODUCTION Department ofPhysicsandAstronomy,JohnsHopkinsUniversity;SpaceTelescopeScienceInstitute Harvard-Smithsonian CenterforAstrophysics,60GardenStreet,Cambridge,MA02138 OF SEYFERTGALAXIESANDLINERS Received 1990September4;accepted1992January7 Richard Burg John Huchra ABSTRACT 90 AND correlation function,forSeyfert galaxiesrelativetothatof normal galaxies. spatial distribution—inparticular,thethree-dimensional this surveyhasalreadybeenpublished(HWD). sample of~2400galaxieswithessentiallycompletespectro- be constructed.TheCfARedshiftSurvey(Davis,Huchra, & scopic information.ApartiallistofnewAGNsdiscovered in dispersion spectroscopy.Fortunatelysuchasamplecanindeed missing objectsaresystematicallythefaintestinsample. step inclassificationofanobjectasAGNisintermediate- effective, butdependscriticallyontheassumptionthat Latham 1983;Huchraetal.1983)isamagnitude-limited use aspectroscopicallycompletesample.Themostimportant the observedsample.Thisassumptionisincorrectwhen redshift distributionofmissingobjectscanbeestimatedfrom way, theymodifythedifferentialnumberofobjectsintheir To correctfortheincompletenessinsamplesconstructedthis Survey whichconsistsofall 2399galaxiesinthemerged samples toachieveameanVIVof0.5(e.g.,Huchra&Sargent based onlow-dispersionspectroscopy. objects intheirsamplesbyincreasingthelimitingmagnitude. nucleus andparentgalaxyisveryimportant.Last,ashasbeen Dahari 1983),manyobjectsaremistakenlyclassifiedasAGNs repeatedly pointedoutbyOsterbrock(e.g.,& harder tofindthanSeyfert1galaxies;contrastbetween Davis 1982,hereafterHWD).Also,Seyfert2galaxiesare 1973; Terebizh1980;Meurs&Wilson1984).Thisissomewhat m A secondpaper(Burg&Huchra1992)willdiscussthe The sampleweusehereisderived fromtheCfARedshift One obviousbutdifficultsolutiontothesedilemmasis Some earlyworkersartificiallyenlargedthenumbersof 2. THESAMPLE 1992ApJ. . .393. . .90H more recentlyidentified,bright galaxiestheonlyphotometry de Vaucouleurs1983). available hasbeendoneinlarger apertures(see,e.g.,Longo& well-observed objectsthisusually means10"or15",butforthe the smallestaperture,accurate photometryavailable.Forthe Vaucouleurs (1983,1985).The quotedphotometryrepresents Gonzalez (1985)andvariouscompilationsbyLongo& de heliocentric cz(theIAUstandard).TheUBVphotometry(cols. (~0.3 magrms)forourpurposes.Thevelocities(col.[5]) are (Edelson 1987).Themagnitude(col.[4])isintheuncorrected 2J(0)-Zw system(Huchra1976),whichissufficientlyaccurate (cols. [2]and[3])comefromClements(1981,1983; and [7], [8],and[9])comesfromthemastercatalogofCruz- private communication),fromtheZwickycatalogor the examined andshownoevidenceofnonthermalactivity. Second ReferenceCatalogorfromEdelson’sradiopositions our spectralrange;thespectraofthosegalaxieshavebeen the samplehaveredshiftsthatwouldplaceHalineout of catalog limitedatm=14.5.Lessthan0.1%ofthegalaxiesin galaxy (anellipticalthatZwickymissed!)tothemerged The Nilsoncatalogisdiameter-limitedandaddsonlyonenew catalog ismagnitude-limitedto1magfainterthanoursurvey. Osterbrock (1987). Additional informationonclassificationcanbefoundin trast, andtheS/Nofspectrum)wasclassifiedasatype1. “ subclassify”theSeyfertgalaxiesintofractionsbetween1and complete samplemagnitudelimit.Wehavenotattemptedto ponent (theexactcriteriawilldependonvelocity-width,con- 2; anyobjectwithaneasilyvisiblebroadpermittedlinecom- galaxy, notaSeyfert2.Thisobject,however,isfainterthanthe was indoubthavebeenreobservedwithhighersignal-to-noise object inHWD,NGC7672,isactuallyanarrowemission-line ratio (S/N)and/orathigherdispersion.Notethatonesuch plots (cf.theexamplesinHWD).Objectswhoseclassification classification isbasicallyaspectroscopiconebasedonthepres- activity. Galaxyspectraareclassifiedbyvisualinspectionof ence ofemissionlinesindicativenonthermal(nonstellar) objects inthissamplehavebeenclassifiedasHWD;our Markarian andcoworkersaswellotherAGNhunters.The nuclei (andarethusextremelyunlikelytobeAGNs). companions totheMilkyWay,forwhichitisdifficult 98.5% ofthissamplefromtheCfAsurvey.Theremaininggal- Zwicky-Nilson catalog(Zwickyetal.1961-1966;Nilson1973) b obtain opticalspectrabecausetheydonothaveidentifiable that satisfythefollowingcriteria: observers, orlowsurfacebrightnessdwarfgalaxies,likethe ally havebeenwellobservedspectroscopicallybymany copy coveringtherange4600-7000Âisnowavailableforover (Note thatmisessentiallythesameas).Opticalspectros- axies areeitherthebrightestobjectsinsurveywhichgener- and either or Zwpg Our catalogofAGNsisgiveninTable1.Thecoordinates The CfAsampleislimitedbymagnitude.Zwicky In addition,thispartoftheskyhasbeenwellobservedby © American Astronomical Society • Provided by the NASA Astrophysics Data System ô >—2.5°andb<-30°. n <5 >0°andb40°, n m <14.5, Zw AGN SPACEDENSITY91 -1 mean VIVvaluesof~0.5,the expectationvalueforacom- plete, approximatelyuniform sample.Othergroups,using as afunctionoflimitingmagnitude. TheSeyfertsampleshave covers alargeareaofthesky. Table2showstheV/Vforour samples ofSeyfert1galaxies, Seyfert2galaxies,andLINERs reaches toover100Mpc(H =100kmsMpc)and are generallyluminous,cf.Huchra&Sargent1973,andbelow) CfA RedshiftSurveylimitforluminousgalaxies(andSeyferts effects (evolution)arenegligible—thehighestredshiftsonly a fewtenths—andlocalclusteringisalsoinsignificant—the the Seyfertgalaxiesinoursampleweexpectthatcosmological less uniformlydistributed(e.g.,Huchra&Sargent1973). For for samplecompletenessifitisknownthatobjectsaremore or whether ornotitisbiased.Schmidt(1968)appliedatechnique uniform distributionsinspace.Thistestcanalsobeusedto test called theV/Vtesttodetermineifsamplesofobjects had m (HWD). Adetaileddiscussionoftheradiopropertiesthis sample canbefoundinEdelson(1987). (24% oftheSeyfert1and43%2)arespectro- scopically discoveredobjectsuncoveredintheCfAsurvey m three otherobjects.AmajorfractionoftheSeyfertgalaxies scopically consideredequivalenttoaSeyfert1galaxy,and 2 galaxies,33LINERs,oneQSO,whichcanbespectro- later, relativelyhighS/Nspectraareneededtodetectthese 0 survey. objects, thusthereisabiasagainsttheirdiscoverybytheCfA surveys ofStauffer(1982)andKeel(1983).Aswewilldiscuss original surveyofHeckman(1980)orinthemorerecent found thatarebrighterthan14.5andyetnotinZwicky’s limited. Inaddition,almostalloftheobjectsclassifiedas for 3C273.Thesampleisneitherredshift-limitednordiameter- lists. Forexample,allofthePGobjects(Schmidt&Green magnitude-limited. Veryfewextragalacticobjectshavebeen Seyferts havestrong,well-observedemissionlines. m galaxy byFilippenko&Sargent(1989).Thiswasoneofthefew include NGC4395whichwasdiscoveredtobeaSeyfert1 (1983). Weshouldnotethatearlyversionsofourlistdidnot objects wedidnothaveaspectrumfor. veyed forotherbright(m<16)QSOsbySchmidt&Green important exampleofthedifficultiesdefiningacomplete sample ofAGNs.Notealsothatthisareahasbeenwellsur- selection criteriaofequations(l)-(3),andwethinkitactsasan sample. Weincludeit,however,becauseitdoessatisfythe normal rangeofparametersforalltheotherobjectsinthis 1983) satisfyingourcriteriawerealreadyinthesampleexcept them further.Thequasar3C273isfarremovedfromthe averaged luminositydensityofAGNs.Wewillnotdiscuss the generalformofluminosityfunctionoronmean presence oftheselastobjectshasnosignificanteffectoneither 4156, discussedbyElvisetal.(1981),andtheonlyquasarinside intermediate-strength X-raygalaxies,NGC3862and which isabrightBLLacertae-typegalaxy,thetwo the surveyboundariesbrighterthan14.5mag—3C273.The nuclear emission-lineregions(LINER).TheseareMrk421 in additiontoordinarySeyfertgalaxiesandlow-ionization The firstquestionwewanttoaskaboutoursample is The presentsamplecontains26Seyfert1galaxies,23 Most oftheLINERsinthissamplewereidentified It isimportanttopointoutthatthissampleprimarily We haveincludedinthislistfourobjectsclassifiedasAGNs 3. COMPLETENESS:THEV/VTEST m 1992ApJ. . .393. . .90H NGC 5252. NGC 5195. NGC 5194. NGC 5033. NGC 5005. Mrk789 ... NGC 4826. NGC 4579. NGC 4438. NGC 4569. NGC 4501. NGC 4419. Mrk 231... NGC 4486. NGC 4450. NGC 4388. 1335 +39.. NGC 4395. 3CR273 ... Mrk205 ... NGC 4303. NGC 4278. NGC 4258. NGC 4253. NGC 4235. NGC 4192. NGC 4156. NGC 4151. NGC 4111. NGC 4051. NGC 4036. NGC 3998. NGC 3982. NGC 3921. NGC 3898. NGC 3862. NGC 3786. NGC 3642. NGC 3516. A1058 +45 NGC 3362. Mrk 421... NGC 3227. NGC 3185. NGC 3079. NGC 3080. NGC 3031. NGC 2911. NGC 2841. NGC 2768. NGC1144. NGC 1068. NGC863 .. 0152 +06.. Mrk573 ... Mrk993 ... IZW1 A0048 +29 Mrk335 ... Mrk334 ... Name (1) © American Astronomical Society hm 12 3512.0 13 3544.4 13 3528.4 13 2955.4 13 2752.2 13 2745.6 13 1109.2 13 0837.2 12 5416.8 12 2513.6 12 5405.4 12 3418.6 12 2927.6 12 2817.4 12 2558.2 12 2425.2 12 2633.4 12 2318.0 12 2314.4 12 1933.5 12 1921.6 12 1736.0 12 1629.4 12 1555.2 12 1436.6 12 1115.6 12 0818.2 12 0800.4 12 0431.8 12 0036.1 11 5853.4 11 5520.9 11 5353.0 11 4828.2 11 4636.0 11 4229.6 09 5834.8 11 3704.9 11 1925.2 09 5714.2 09 5130.0 11 0322.8 11 0140.6 09 3105.4 10 5842.5 10 4215.2 09 1834.6 09 0745.0 10 2046.8 02 5238.9 02 4007.0 10 1453.4 02 1200.5 01 4122.9 01 5244.7 01 2242.7 00 5057.9 00 4853.1 00 0345.2 0035?6 R.A. (1950) (2) 04 47 47 3148 47 2718 39 2431 21 5706 36 5130 37 1924 -0 2307 02 1942 33 4900 -0 1331 -0 5958 57 0840 04 4506 30 0518 11 2144 75 3515 29 3336 47 3500 07 1806 12 0534 13 2624 13 1707 14 4142 15 1924 12 4006 17 2142 12 5618 43 2042 44 48 39 4503 39 4102 62 1030 Bright ActiveGalacticNuclei 15 1048 55 2418 55 43 55 2124 56 2148 32 11 59 2100 72 5020 45 5522 06 5135 19 5302 38 2843 20 0707 21 5618 55 24 69 18 51 1118 60 1430 02 0557 06 2202 13 1703 10 2236 31 5236 29 0746 21°40'54" 12 2518 19 5529 Decl. (3) TABLE 1 14.50 14.20 14.50 10.94 11.00 10.85 14.10 11.50 10.58 12.00 10.49 10.30 11.29 12.23 13.10 10.84 12.20 14.50 10.90 11.20 13.70 12.86 11.00 14.28 11.20 11.50 12.08 11.87 11.79 12.45 13.40 11.60 14.00 13.50 11.96 12.30 14.00 14.10 13.60 12.20 13.23 11.20 14.50 13.82 10.27 11.48 13.20 14.00 10.30 9.03 9.60 14.50 14.00 14.00 14.50 14.30 14.00 14.40 9.19 8.15 (4) 47352 20978 12287 -245 -182 -110 10602 6926 6023 9318 18116 10763 2270 2535 1022 3836 1486 1020 2300 1265 1957 1585 6766 6462 5895 2737 2540 1401 9230 1047 1188 1158 8318 8778 1584 1152 1237 3254 1114 8641 4625 7891 5208 5178 6605 1363 1109 -44 7757 474 414 558 892 318 635 449 970 794 674 (5) 637 3 Type 2 2 L L L L L L L L L L 2 1 L 1 1 L L L 1 1 X 1 L 1 L 1 L 2 1 L L L X 1 L 2 2 B 2 (6) L 1 L 1 L Provided bythe NASA Astrophysics Data System L L L 2 2 2 1 2 2 1 2 1 1 1 14.21 14.68 12.30 12.89 10.39 11.09 11.72 12.09 13.85 11.69 12.20 11.71 12.05 12.86 13.19 13.13 12.78 13.24 12.88 11.26 11.65 13.55 12.27 11.21 13.77 11.91 11.22 12.64 11.20 11.70 13.35 11.83 14.15 13.74 12.71 12.60 13.50 13.52 13.26 15.07 10.34 13.92 10.45 11.90 14.41 10.44 13.94 13.64 13.43 9.62 14.07 13.85 14.42 (7) V 0.57 0.84 0.82 0.89 0.86 0.85 0.97 0.83 0.93 0.93 0.21 0.57 0.82 1.00 0.40 1.21 0.78 0.95 0.78 0.72 0.99 B-V 1.05 1.00 1.01 0.92 0.89 0.58 0.90 0.80 0.96 0.98 0.79 0.88 0.78 0.63 0.51 1.01 0.82 0.94 1.05 0.72 0.99 0.56 0.97 1.04 0.36 1.20 0.41 1.04 0.13 1.01 1.00 1.04 (8) -.18 -.85 -.18 -.94 -.57 -.30 U-B -.55 0.34 -.11 0.73 0.11 0.40 -.23 0.27 0.36 0.59 0.14 0.50 0.17 0.65 0.64 0.62 0.39 -.80 0.08 -.01 0.19 0.53 -.80 0.30 0.06 -.70 0.48 0.07 0.48 0.05 0.58 0.58 1.40 0.39 0.54 0.46 0.20 0.50 0.60 0.80 0.50 0.54 0.22 0.09 0.23 0.31 (9) 1992ApJ. . .393. . .90H _1 et al.1989).Wefeelthatthesmallnumberofstatisticsand earlier versionsofourlist,findthatthereisevidenceforincom- luminosity sources,doesnotallowforastrongconclusion.The redshifts oforder1000kms,whichaffectsonlylow- pleteness, atthe2-3alevel,forlow-luminosityobjects(Persic pected. LINERscanberecognizedonlybyunusualemission galaxies fainterthan13thmag,andappearstobecomplete sample isthustreatedtobecomplete. sizable systematicproblemduetodensityhomogeneitiesat only to11.5or12.0.Thisdisappointingresultisnotunex- 13.5 0.31+0.09 14.0 0.35+0.08 14.5 0.46+0.06 12.5 0.26+0.13 13.0 0.29+0.11 11.0 11.5 12.0 0.30+0.14 The LINERsample,ontheotherhand,containsalmostno © American Astronomical Society • Provided by the NASA Astrophysics Data System V/V n m Seyfert 12LINERs NGC 4253=Mrk766;4388Arp120;4486M87;5194M51VV185; 270; NGC5695=Mrk686;5929Arp90IZw112Turner126A;7603530; 7674 =Mrk533VV343. 3227 =VV209;NGC3786Mrk744Turner39A;38623C264;3921430IZw28; 5195 =M51VV1Arp85;Mrk789VIIIZw323;NGC5256266I67;5283 NGC 5256. NGC 5347. NGC 5273. NGC 5283. NGC 5371. NGC 5674. NGC 5675. NGC 5548. Mrk279 ... Mrk461 ... NGC 5899. NGC 5695. NGC 5940. NGC 5929. NGC 7469. NGC 6104. Mrk 817... NGC 7674. NGC 7479. 2237 +07.. Mrk 841... NGC 7743. NGC 7682. 11481 Mrk 530... 3 26 0.47±0.06 14 0.48±0.08 10 0.29±0.12 Notes—Mrk 334=IVZw1;NGC863Mrk590;3031M81;30801243; Type1=Seyfert;22;Xweak-linedX-raysource;LLINER;BBLLacertaeobject. 4 0.09±0.29 7 0.27±0.14 5 0.54±0.14 Name TABLE 2 F/F Test m (i) 13 3941.2 13 3614.7 23 0226.4 23 0044.5 13 4504.4 13 3955.1 23 4148.6 23 2630.7 23 2524.4 23 1652.6 23 1622.6 14 1543.7 13 5339.0 13 5152.5 13 5105.4 22 3746.5 14 3519.7 14 3457.9 14 3122.5 14 3036.4 15 1314.4 15 0136.3 16 1440.1 15 2851.3 15 2418.9 R.A.(1950) 23 0.08±0.0533 13 0.11+0.0532 4 0.23±0.0627 4 0.14±0.0628 6 0.11+0.0530 1 0.35±0.0624 (2) 0.44 +0.0812 0.38 +0.0717 -0 0139 AGN SPACEDENSITY 48 3153 05 4038 40 4224 67 5536 25 2159 69 3316 33 4400 34 2357 35 5421 07 3738 41 5041 42 1400 08 3618 07 4734 36 3119 08 3013 05 3757 36 4702 59 0039 09 3918 03 1528 35 4950 10 3756 1Í 0306 Decl. (3) TABLE 1—Continued 14.30 14.10 13.18 14.50 12.71 11.59 14.50 13.70 14.00 13.10 14.00 14.00 13.90 14.30 14.10 12.79 11.93 13.13 14.30 14.30 14.50 14.40 12.50 14.30 13.60 (4) emission, andthiscanbedetectedonlyinhighS/Nspectra. line ratios,inparticular,thepresenceofstrongOI6300Â fixed 3"2inwidth)containlargerandfractionsofthe nuclei ofthistypegalaxydonotcontributesignificantlyto incompleteness. calculation ofthespacedensitybelow,wemustcutsample nosity parentgalaxiesorveryhighluminositynuclei.In the redshifts withfixedslitsizes(theRedshiftSurveyslitsarea the totalgalaxyluminosity.Observationsofgalaxiesatlarger magnitudes versusintegratedinthecomputation surrounding galaxy.Wethusmightexpecttofindonlynearby More importantly,thecontrastproblemissignificant.The of LINERsat12thmag.Eventhen,thesamplesuffersfrom LINERs andthosehigherredshiftobjectswithlowerlumi- comparison oftheSeyfertto quasar luminosityfunctionisthe has stressedthattherelevantquantityforbothcomputa- cated. Veronusedmagnitudes determinedinsmallapertures, exist onreasonabletimescales. nuclear magnitude.Unfortunately, thereistodatenosample tion oftheAGNcontribution totheX-raybackgroundand of theSeyfertluminosityfunction.Veron(1979),inparticular, of objectsselectedbynuclear magnitudes, andnoneislikelyto There hasbeenconsiderabledebateontheuseofnuclear In addition,thedefinitionof“ nuclear”magnitudeiscompli- 10921 10160 V 4894 2697 4981 9129 2335 8239 4209 2561 9430 H 4790 2504 2554 7442 3973 1089 2392 7487 8397 6118 8691 5107 8662 1658 (5) 4. INTEGRATEDVERSUSNUCLEARMAGNITUDES 3 Type 2 2 (6) 2 2 2 L 2 L 2 L 1 1 2 2 L 1 L L 1 1 1 1 1 1 1 14.05 13.42 12.70 13.24 14.46 13.76 12.63 12.08 13.60 13.86 14.90 13.40 13.10 13.10 13.85 13.46 13.67 14.01 (7) V B— V 0.77 0.83 0.92 0.69 0.76 0.48 0.98 0.68 0.95 0.31 0.66 0.98 0.80 0.96 0.48 0.94 0.76 0.72 0.94 (8) U—B -.71 -.45 -.57 -.89 -.75 -.20 -.03 -.21 0.16 0.31 0.06 0.04 0.52 0.26 0.28 0.23 0.44 0.30 (9) 93 1992ApJ. . .393. . .90H magnitudes, itisstillpossible toaddressthequestions:(1) objects totheX-raybackground? nitude areAGNs,(2)Whatis theintegratedvolumedensityof What fractionofgalaxiesasa functionofgalaxyabsolutemag- Seyfert galaxies,andthus(3) What isthecontributionofsuch (1987) hasshownthattheradioluminosityiswellcorrelated with theintegratedopticalluminosityofparentgalaxy but et al.,privatecommunication)todeterminethenonthermal with aslopesteeperthanunity. nuclear luminositiesforthegalaxiesinthissample.Edelson nosities. Programsareunderway(e.g.,Edelson1987;M.Elvis late suchquantitiesastheX-raytoopticalluminosity of cantly changetheshapeornormalization(integratednumber It isthusstilluseful(althoughprobablynotoptimal)tocalcu- constant offsetofabout1mag,withalargeamountscatter. from thesmallestavailableaperture(Table1).Thereisno plot ofintegratedB(0)-ZwmagnitudeversustheB Seyfert galaxiesintermsoftheirintegratedopticallumi- of objectsperunitvolume)thederivedluminosityfunction. It isunlikelythatuseofsmall-aperturemagnitudeswillsignifi- metry totheintegratedmagnitudes(asVerondid).Figure1isa significant departurefromalinearrelation,althoughthereis we candoatthemomentiscontrastsmall-aperturephoto- and almostallhaveopticalbroad-bandphotometry.Thebest of objects. radio sources,andSeyfert2galaxiesaregenerallyweakX-ray To makemattersworse,Seyfertgalaxiesarenotverystrong identifying nonthermalsourcesinlargenumbersofgalaxies sources, sosurveysatotherwavelengthsalsoyieldamixedbag are appliedonlyto“integrated”magnitude-limitedsamples. component areirrelevant.Inanycase,opticaltechniquesfor nant thaterrorsinthedeterminationofunderlyinggalaxy objects orthosewherethenuclearsourceissodomi- nucleus. Thisispossibleintheopticalonlyfornearest remove thestellarcomponentfromdisk,bulge,andeven measure onlythecontributionofnonthermalsource— in aredshift-dependentmanner.Ideally,onewouldwantto but thisestimatesthecontributionofsurroundinggalaxy galaxies areopencircles,(b)Thesameexceptnowplottedasabsolutemagnitudes. 94 HUCHRA Independent ofone’sviews on integratedversusnuclear The sampleofgalaxiesanalyzedhereisapparentlybright, Fig. 1.—(a)ApparentintegratedBmagnitudes[intheJ3(0)-Zwickysystem] © American Astronomical Society • Provided by the NASA Astrophysics Data System Fig. la & BURGVol.393 t. small-apertureBmagnitudes.Seyfert1galaxiesarefilledcirclesand2 ll n _1- -1 in Table3and inFigures2and3.The spacedensityof lute magnitudebins.Theresults oftheseanalysesarepresented small numberstatisticsandplacement ofobjectsintheabso- (1977) andhaveessentiallythe samestatisticalefficiency,but the F/Ftechniqueisslightly lesssusceptibletobiasdue complete detailsoftheanalysiscanbefoundinAppendixA. second istousetheV/Vtechnique asdescribedbyHuchra& volume atthecenterofabsolutemagnitudebin. The the numberofobjectsperbin,andcalculatingmeansearch Sargent (1973).Bothhavebeen describedindetailbyFelten simply binningthesamplebyabsolutemagnitude,counting differential luminosityfunctionsfromcompletesamples.One is correct forthetendencygalaxiestoclusteraroundour own nosity rangecoveredbytheSeyfertandLINERsamples.More dividing throughbytheintegralofcorrelationfunction to and hasnosignificanteffectonthespacedensityinlumi- tendency ofgalaxiestocluster.Thiscorrectionisessentially tion hasbeenappliedtothesearchvolumecorrectfor the primarily above\b\=40°.Wenoteonceagainthatthemag- (Felten 1977).ThisfollowsbecausetheSandage(1973)absorp- nitudes usedareontheB(0)-Zwickysystem.Asmallcorrec- tion correctioniszeroabove\b\=50°,andtheCfAsample correction totheluminositydensitywillbelessthan10% latitude dust—Lowetal.1984;Knude1986),thentheoverall galactic absorptioncorrectionisnearlycorrect,asmostnew observations seemtoindicate(e.g.,theIRASresultsonhigh- high galacticlatitude,andifSandage’s(1973)prescriptionfor (more forthefaintendoffieldfunctionthananythingelse, not correctforgalacticabsorption.Oursampleismostlyat We assumeaHubbleparameterof100kmsMpc,anddo see Aaronsonetal.1982)withaninfallvelocityof300kms. and fieldgalaxies.WecanusetheparentsamplefromCfA consideration isuniformtreatmentofoursamplesAGNs m Redshift Surveytoderivethefieldluminosityfunction. nosity functionof“normal”galaxies,sothemostimportant m straightforward. Ouroverallgoaliscomparisonwiththelumi- There aretwosimpletechniquesforthedetermination of We correctoursamplefortheeffectsofaVirgocentricflow The calculationoftheluminosityfunctionisrelatively 5. SPACEDENSITIES Fig. lb 1992ApJ. . .393. . .90H approach andfoundM*=—19.3a~—1. sample usedinthispaperutilizingadensity-independent discovered withothersurveys, andthensome.Theonlysys- fitted withahighdegreeofconfidence.DeLapparent,Geller, the 2400galaxiesinCfA sample, wehavefoundallAGNs low-luminosity AGNstodate. Inourspectroscopicsurveyof limited redshiftsurveyhasyielded themostcompletelistof & Huchra(1989)reportaSchechterfunctionfittedtothe field lation betweenbins,didnotallowparametricmodelsto be that thesmallnumbers,togetherwithhighdegreeofcorre- We haveusedanonparametricdensity-independenttechnique constraints onthespatialuniformityofgalaxydistribution. to verifytheshapeofluminosityfunctionbuthavefound formly. Thedensity-independenttechniquestradeoffinforma- change withpositionandthatthegalaxiesaredistributeduni- tion abouttheabsolutespatialdensityinordertorelax the luminosityfunctionassumeboththatitsshapedoesnot density-independent techniques(Lynden-Bell1971;Turner and Veron1985;Huchra1991). incomplete) samplesofseveralhundredAGNs(Veron-Cetty few SeyfertnucleiareobservedingalaxiesfainterthanM~ importantly, weobservenoAGNsinfaintgalaxies.Very,very high-luminosity cutoffparameter,M*(Schechter1976).More nosity functionatthelow-luminosityend,and iance betweenthederivedvalueofa,slopelumi- 1979). Theabovestandardtechniquesforthecomputationof especially fortheAGNssamples.Thereisaverylargecovar- Table 3.Weadvisecautionintheuseoftheseparameters, luminosity functions,andtheirparametersarealsogivenin mag. Thetwotechniquesgivethesameresults(astheyshould). LINERs hasbeencomputedfromthesamplelimitedto12th B — 18,eitherinthepresentsampleormuchlarger(but No. 1,1992 The spectroscopicclassification ofgalaxiesinamagnitude- The shapeoftheluminosityfunctioncanalsobederivedvia Schechter functions(Schechter1976)havebeenfittedtothe © American Astronomical Society • Provided by the NASA Astrophysics Data System b 0(A*b ^-18) Total F/F.
4 04 5 \ 6 öß O
Mb Fig. 2.—Differential luminosity functions of Seyfert 1 (filled circles), Seyfert Fig. 3.—Differential luminosity function of all Seyfert galaxies (both l’s 2 galaxies (open circles), and LINERs (squares). Error bars represent only the and 2’s, open circles) compared to the luminosity function of field galaxies internal statistical error in each magnitude bin. The “hump” in the LINER (filled circles) derived from the CfA Redshift Survey. density at —19.5 almost certainly represents an overestimate of the true density due to the presence of the Local Supercluster.
much flatter than that of normal galaxies, we expect the frac- Most of these differences can be explained by the selection tion of AGNs to rise dramatically in fainter, high-redshift techniques used for assembling the different surveys. Objective galaxy samples (Burg 1987). prism searches that rely on finding emission-line objects will, in In the light of predictions of the unified model of AGNs general, be more sensitive to sharp emission-line objects for (where Seyfert 2 galaxies are obscured Seyfert 1 galaxies, cf. galaxies with lines of similar equivalent width. Thus, when the Lawrence 1987; Blandford 1990), a number of authors have narrow lines of the Seyfert 2 galaxies are near the limit of examined the relative numbers of Seyfert 1 and 2 galaxies in spectral resolution for the objective prism, Seyfert 2 galaxies different samples. Osterbrock & Shaw (1988) examined the will be more easily selected. UV excess searches, on the other Wasilewski sample and estimated that the relative number hand, will preferentially select the less reddened Seyfert 1 gal- density of Seyfert 2 to Seyfert 1 galaxies is approximately 8. axies. Our sample, based on total blue magnitudes, is much less Salzer (1989), in his analysis of the Michigan Emission Line likely to be intrinsically biased by type, and thus the factor of Survey, finds equal numbers of Seyfert 2 and 1 galaxies in the about 2 between the space densities of the Seyfert 2 and Seyfert sample which corresponds to a relative space density of 5. In 1 galaxies is more likely to be the true ratio. our blue, magnitude-limited sample, we also find approx- This paper presents a uniform finding list of apparently imately equal numbers of Seyfert 1 and Seyfert 2 galaxies. bright AGNs that has for a number of years been a useful However, we find, integrating down to an absolute blue inte- starting point for detailed investigations. grated magnitude of —18, that the relative space density of Seyfert 2 to 1 galaxies is only 2.3 ± 0.7 (Table 2). From Figure We would like to thank Yoram Avni, G. de Zotti, Rick 2, we also note that there is not a strong change in this ratio as Edelson, Alberto Franseschini, Martin Elvis, Herman Mar- a function of luminosity, although there is an apparent dip in shall, and Richard Mushotzsky for stimulating discussions. the density of Seyfert 2’s at —20. Suggestions from the anonymous referee have substantially Meurs & Wilson (1984), from a sample of Markarian Seyfert improved and updated the paper. Typing services again have galaxies, find an even higher fraction of Seyfert 1 galaxies. been generously provided by Fang, Inc.
APPENDIX A
CORRELATION FUNCTION CORRECTION TO THE LF For both of the two simple methods of deriving the space density of galaxies that have been discussed in this paper—the standard binning techique and the 1/Vm technique—one should apply a small correction due to the known existence of the clustering of galaxies. Essentially, we are deriving the mean space density of galaxies but are not sampling from a random locus in space but rather in shells surrounding a galaxy. Since galaxies cluster, this will cause us to overestimate the density of galaxies when we sample only small volumes around us. This bias is particularly important at low luminosity where, in a magnitude-limited sample, the effective or limiting distance may be much smaller than the correlation length so that a straight application of the above techniques should significantly overestimate the true volume density. The excess number of galaxies expected because galaxies cluster out to a given radius, r, is
AL Ne 3 Ç(r)d r . (1) N„ N,,
© American Astronomical Society • Provided by the NASA Astrophysics Data System X O'!o No. 1, 1992 AGN SPACE DENSITY 97 ^ If the correlation function, ¿(r) is of the standard form a (2)
(Peebles 1980), and if the correlation function is assumed to be independent of luminosity, then the simple integral
2 y y ne/ni r ~ r 0dr (3) '-4*f
gives the excess. We can then treat the problem as one of correcting the effective volume searched and modify either Vm of the 3 limiting volume of a given absolute magnitude bin. The “volume” correction factor, C, defined by = CF0, where V0 = (4/3)7rr , becomes 3 y Anrinr r ~ C = 1 + * o (4) 3 - y v0 In real samples (including this CfA survey, Davis & Peebles 1983), the correlation function appears to turn over at separations - 2r0. If the correlation function steepens to a slope nearer 3.5 at 2r0, a more reasonable approximation for the excess is given by m2ro C 2 y y s 15 ne/n, r ~ r 0dr + 2" j 2rl r dr . (5) J2r0
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