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1987ApJ. . .318. .1613 previous resultsobtainedfrom otherinfraredflux-limited magnitudes andnuclearactivity ofoursamplewiththosea metry ofallobjectsinthesamplewasalsoobtainedbyusing structed anew60gmluminosityfunctionandcompare it to the IRASsurveydatabase.Fromthesedata,wehave con- Geller, andHuchra(1986).Accuratefour-colorinfraredphoto- samples ofgalaxies.Finally, wecomparetheabsoluteblue selected galaxiescarriedoutinthisregionbydeLapparent, the entiresamplebyextendingredshiftsurveyofoptically joint facilityoftheSmithsonianInstitution andtheUniversityofArizona. brighter than2Jyat60gm.Wehaveobtainedredshiftdata for important consequencesfortheanalysisoffainterX-ray samples (Gioiaetal1984). among X-rayselectedgalaxiesandhasbeenshowntohave luminosity functionatitshigh-andlow-luminosityextremes. and whetherdifferentclassesofgalaxiescontributetothe necessary toknowtheinfraredluminosityfunctionofgalaxies, Such asubdivisionoftheluminosityfunctionhasbeenfound of evolutionthespacedistributionIR-brightgalaxies,itis sion fromdustyinterstellarandcircumstellarcloudsinthe The surveyisinsensitivetoobscurationbydust,thoughemis- plete samplesofgalaxiesselectedatfar-infraredwavelengths. Robinson etal.1984).Tointerpretthesourcecountsinterms Milky Waycausesconfusionnearthegalacticplane(Rowan- The AstrophysicalJournal,318:161-174,1987July1 © 1987.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. 1 The presentstudyfocusesonacompletesampleofgalaxies The IRASsurveyoffersthefirstopportunitytostudycom- Workreportedhereisbasedonobservations obtainedwiththeMMT,a 10 2 h 82 Subject headings::photometry—infrared:sources sample. similar inbothsamples,suggestingthatnuclearactivityisnotastrongcontributortotheinfraredfluxthis IRAS galaxiescanbeusedtodeducethemassdistributioninuniverse.Thepercentageofactiveis optically selectedgalaxiesinthecoreofComaCluster,raisingquestionwhethersourcecounts space distributionofthetwosamplesdiffer:densityenhancementIRASgalaxiesisonlythat in thesensethatIRASsampleincludesfewgalaxiesoflowabsoluteblueluminosity.Wealsofind surveyshowthattheyaremorenarrowlydistributedinblueluminositythanthoseopticallyselected, leading tothesuggestionthatobservedluminosityfunctionisproducedbytwodifferentclassesofobjects. distinction betweenthemorphologyandinfraredcolorsofmostluminousleastgalaxies, below L=10theluminosityfunctionflattens.Thisisinagreementwithpreviousresults.Wefinda to 5xlO^iTo/lOO)L.The60jtmluminosityfunctionatthehigh-luminosityendisproportionalL~; lying theregion82Jyand I. INTRODUCTION 1 A STUDYOFFLUX-LIMITEDSAMPLEIRASGALAXIES Received 1986September3;acceptedDecember11 Beverly J.SmithandS.G.Kleinmann Harvard-Smithsonian CenterforAstrophysics Steward Observatory,UniversityofArizona University ofMassachusetts J. P.Huchra ABSTRACT F. J.Low 161 AND h having m<13intheselected region;21arenotinour incompleteness duetolargegalaxies, wesearchedtheUppsala cally LargeGalaxies(Riceet al.1986).Asafurthercheckon Jy at60/mi.Thisobjectwas addedtoourlist,andaccurate IRAS photometrywasobtained fromtheIRASAtlasofOpti- (0 ~9'),itsfluxwasunderestimatedinthePSCtobeonly 0.9 General CatalogofGalaxies (Nilson 1973).Itlists39galaxies listed inthePSC,butbecauseofitslargeangularextent with thenearbyspiralgalaxyNGC4725.This was clouds (Lowetal.1984).Theremainingsourcewasidentified our sample,andsixwerefoundtobecondensationsincirrus sky. Ofthese,sevenwereslightlyextendedgalaxiesalready in This cataloglists14objectswithS(60)>2Jyinourregion of axies oflargeangularsize,wesearchedtheIRASSmallScale ciently highgalacticlatitude(b>20°)thatconfusion with parison ofthespacedistributioninfrared-selectedandblue- Structures Catalog(1986;hereafterSSS)foradditionalobjects. sources mettheselectioncriterion. galactic objectsandinfraredcirrusisminimized.Eighty-six selected galaxies. between 8

FLUX-LIMITED IRAS GALAXIES 167 ; where the quoted uncertainties are the rms dispersion about the energy in the band ^ the average. For the in our sample, 2 L = 4nr Fv Av ,

where Fv is the corrected IRAS flux density and Av is the Î (if) =0.17 ±0.03 bandwidth ( = 3.75 x 1012 Hz; Neugebauer et al. 1984). We calculate r by assuming Ho = 100 km s-1 Mpc-1 and correct- = 0.56 ± 0.10 . ing for 300 km s-1 galactic rotation and deviation from the Feo/ Hubble flow due to infall toward the Virgo Cluster of 300 km One planetary is included in this sample; it has an s-1 as in Huchra and Geller (1982). Under these assumptions, intermediate spectrum, with F(60) > F(25), but F(100) < F(60). the most luminous galaxy in the sample, Arp 220, could be detected above the flux limit of 2 Jy at up to 0.15. IV. OPTICAL OBSERVATIONS V. THE INFRARED LUMINOSITY FUNCTION AT 60 fim Spectra with a resolution of 6-7 Â covering 4600-7200 Â The distribution of luminosities and the luminosity function were obtained at the F. L. Whipple 1.5 m telescope and at the 47rJ_ J_ MMT using a photon-counting Reticon system (Latham 1982). Q>(Li) = y The slit sizes used are 3'.'2 x 6"4 at the 1.5 m and 1"0 x 3'.'0 at Q AL,. t Vj the MMT. Several galaxies were observed in the confused are shown in Figure 3 and tabulated in Table 5. Here Q/4n is cases; all our pairs appear to be physically associated, i.e., at the fraction of the sky covered by this survey, AL¿ is the bin the same redshift. Table 4 lists the galaxies in our sample with width, and Vj is the volume of the universe out to which a the equivalent widths of the Ha, Hß, [O m] 25007, [O i] galaxy of luminosity L is observed at our flux limit. Across the 26300, and [N n] 26585 lines. Columns (7), (8), and (9) give the top of Figure 3 we indicate the distance to which a galaxy of apparent blue magnitude, the heliocentric recessional velocity, the corresponding luminosity can be detected at the imposed and the uncertainty in the velocity. For galaxies brighter than mB = 15.7, the magnitudes were taken from the Zwicky Catalog (Zwicky et al. 1961); these are accurate to 0.3 mag TABLE 5 (Huchra 1976). For the six galaxies not in Zwicky’s list, eye 60 fim Luminosity Function estimates were made by one of us (J. P. H); these were checked 3 by determining the correlation between size and apparent log (L/Lq) {L) (Mpc mag ^ N magnitude for the brighter galaxies, and, assuming the same 8.4 4.7 x 10~3 1 2 “surface brightness” for the fainter galaxies, using their 8.8 1.2 x 10“3 8 angular sizes to estimate their brightness. This process showed 9.2 4.9 x 10" 8 9.6 9.5 x 10“4 7 that the eye estimates were typically accurate to 0.5 mag. 10.0 6.9 x 10'4 20 The redshift distribution of our sample is shown in Figure 2. 10.4 1.7 x 10"4 15 The maximum redshift of 0.07 corresponds to a distance of 210 5 10.8 2.5 x 10~6 7 (100/H0) Mpc. The last two columns in Table 4 list the blue 11.2 3.0 x 10"7 4 and infrared luminosities. We define the 60 /mi luminosity as 11.6 4.9 x 10" 2

Fig. 2.—The redshift distribution of galaxies in the sample

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1987ApJ. . .318. .1613 10 -1 2 2 107-23 81 1/2 10 1/2 was studiedbyRiekeandLebofsky (1986);theyalsofound larger sampleofgalaxiescomprisingseveraldifferent flux for L>10L©.Lawrenceetal.(1986)analyzedasomewhat brighter than5Jyat60¡amandalsoderivedaslopeof—2.0 mag. Theslopeisconfinedtoarangeof—1.5—2.2with described byalawoftheform (L)~Lathighlumin- luminosity functionhasaslopeof—2.5atthehighestlumin- limits. Usingtheirtotalsample,theydeducedthattheinfrared tions oftheluminosityfunctioninfrared-brightgalaxies. osities. that thedistributionoftotal infraredluminositycouldbe tion consistentwithours.Alarge, butlesswell-definedsample axies withF(60)>0.5Jyand alsoderivedaluminosityfunc- Vader andSimon(1986)studiedacompletesampleof68 gal- above 0.85Jy,wefindgoodagreementwithourresults(Fig. 3). 68% confidence,andthereducedxis0.60. osities. However,forthesubsetoftheirdatawhichiscomplete Soifer etal(1986)studiedacompletesampleof217galaxies law. ThesolidlineshowninFigure3isabest-fitpowerlawto luminosities thedensityislessthanexpectedforasinglepower Neither yieldedagoodfit;athighluminositiesthedensitylies our dataabove10Lof(L)=1.4x(L/L)Mpc above thatexpectedforaSchechterfunction,andatlow 4 x10LforNGC4062to5Arp220. for Virgocentricmotion.Thederivedluminositiesrangefrom tried bothaSchechter(1976)functionandsinglepowerlaw. flow whicharenotcompletelyeliminatedbyourcorrections to N;wehaveignorederrorsintheluminositiesdue calculated assumingPoissondistributionerrors,proportional limit of2Jy.Uncertaintiesintheluminosityfunctionwere L >10.ThetopmargingivesthedistancetowhichagalaxyofcorrespondingluminositycouldbedetectedatF(60)2Jy. Lawrence etal.(1986).TheerrorbarsareproportionaltoN.histogramisthenumbercountineachbin(rightaxis).lineshowsabest-fit powerlawfor uncertainties intheinfraredfluxesanddeviationsfromHubble IRlR 0o 0 168 0 These resultsareinsubstantialagreementwithotherderiva- To describethesedatainausefulanalyticalform,wehave Fig. 3.—The60fimluminosityfunction.Thefilledtrianglesarefromthissurvey;theopencirclescompletesample[F(60)>0.85 Jy]studiedby © American Astronomical Society • Provided by the NASA Astrophysics Data System 8 9101112 10 2550100250500 DISTANCE (MPC) SMITH ETAL. LOG L/L 0 ing ofwarmcloudsnearthenucleus andcoolercloudsassoci- if dustingalaxiesisconcentrated intwocomponents,consist- ated withthedisk,observed color-luminositycorrelation ably compactinfraredsources (Becklin1986;Low1986).Thus interpretation ofthisphenomenon issuggestedbytheobserva- luminosity hasbeenreportedpreviously,instudiesofother with 60¿unluminosity. ¿un to60fluxratioappearsbecompletelyuncorrelated tion thatanumberofthemost luminousgalaxiesareremark- samples ofgalaxies(Miley,Neugebauer,andSoifer1985). An to 60¿anfluxratioand¿unluminosity.Incontrast,the 25 and amarginallysignificantanticorrelationbetweenthe12 /on between the60/onto100fluxratioandluminosity, Thus thereappearstobeamarginallysignificantcorrelation linear fits(ignoringupperlimits)tothesedataare pares theinfraredcolorswith60¿anluminosity.Thebest searched forluminosity-dependentparameters.Figure4com- nism changesasafunctionofluminositywithinoursample,we log =0.10+0.02L-1.3±0.2,r0.5. 60 A correlationbetween60¿unto100fluxratioand To testwhetherthepredominantinfraredemissionmecha- log ^=0.00+0.04L-0.9±0.4,r-0.01 log =-0.20+0.04L0.8±0.4,r-0.5 60 60 F loo *60 F 60 VI. INTRINSICPROPERTIESOFTHESAMPLE a) InfraredColors 0 5 20 15 O jd p e X QJ y) 1987ApJ. . .318. .1613 8.5 99.510 10.51111.512 © American Astronomical Society • Provided by the NASA Astrophysics Data System LOG Leo ing upperlimits.TheSeyfertgalaxies areindicatedby solid linesgivethebestlinearfitsto the data,exclud- asterisks. Fig. 4.—Infraredcolorsvs.60/imluminosity. The \—IC/}

170 SMITH ET AL. Vol. 318

; may be attributed to an increase in the luminosity of the gives a 99% probability that the IRAS galaxies are not drawn ^ nuclear component. from the same parent population as the CfA spiral galaxies. § The anticorrelation of F(12)/F(60) and 60 ¿mi luminosity However, a Mann-Whitney test shows that there is only a 1 <7 £ may be due to systematic variations in spectral features within difference in the medians. Thus, we conclude that the distribu- ^ the 12 /mi band as a function of luminosity. Spectra of the tions are different in that the IRAS sample excludes galaxies of highest luminosity galaxy in our sample, Arp 220, show that its low and very high blue luminosity, and as a result, has a nar- 12 fim continuum is depressed by strong (t[10 /mi] ~ 2) sili- rower range in blue luminosity. Because of this, the infrared cate absorption (Rieke et al 1985). The observed correlation excess L(60)/L(B) is closely correlated (correlation might result from less obscuration in the less infrared-luminous coefficient = 0.89) with absolute infrared luminosity (Fig. 6). galaxies. Alternatively the correlation might be produced by an The solid line shows the position of a galaxy of MB = —19.2; increasing role of dust emission features within the 12 /mi the dashed lines indicate the dispersion in MB. bandpass in galaxies of lower infrared luminosity. We point out that there is a single galaxy, PSC 13126 + 2452, with an c) Spectral Properties anomalously low 12 /mi flux density; its colors at longer wave- lengths are normal for its luminosity and its optical spectrum is For a rough estimate of nuclear activity in these galaxies, we use a method similar to that outlined by Baldwin, Phillips, and typical of the galaxies in this sample. Terlevich (1981) to classify the emission-line spectra of extra- galactic objects. Galaxies are segregated by type in the [O m]/ Hß vs. [N n]/Ha plane; Seyfert galaxies fall in the range b) Distribution of Blue Luminosities log ([O m]/H/?) > 0.2, log ([N n]/Ha) > -0.3. Galaxies with Figure 5 shows the distribution of our log ([N n]/Ha) < —0.3 are generally classified as H n region IR-selected sample, the Center for Astrophysics (CfA) blue- galaxies. An advantage to using these ratios is that they are selected sample from Huchra et al (1983), and the CfA spirals. relatively insensitive to reddening; a disadvantage is that a This figure clearly shows that the galaxies in our sample have a galaxy’s position on this plot is a function of its metallicity. narrower range of absolute blue magnitude than those of an We classify NGC 4922B and UGC 7064A as Seyfert 2 gal- optically selected sample. The mean for this sample is —19.2 axies. NGC 4253 is classified as Seyfert 1 as log ([O m]/ with a standard deviation of only 0.8. We find that IRAS Ha) >0.3 and broad permitted lines are observed. Nine undersamples galaxies of low absolute blue luminosity. There galaxies are classified as H n region galaxies (see Figs. 7, 8, and also appears to be a deficiency of galaxies of high blue lumin- 9). This method of classifying galaxy spectra has many uncer- osity. A Kolmogorov-Smirnov test gives a 95% probability tainties (see Baldwin, Phillips, and Terlevich 1981), but it does that the two samples are not derived from the same parent give an estimate of the percentage of active galaxies in an population. IR-selected sample. We find 4%, which is not significantly dif- We also see a difference in the blue magnitude distributions ferent from the 2.3% found by Huchra and Burg (1986) for a oï IRAS galaxies and CfA spirals. A Kolmogorov-Smirnov test blue-selected sample, given the small size of our sample and the

CD

<; o in

Cc! w PQ D

Fig. 5.—The distribution of absolute blue magnitudes of the IRAS sample (solid histogram), the CfA sample (dotted histogram), and the CfA spirals (dashed histogram).

© American Astronomical Society • Provided by the NASA Astrophysics Data System C/} 910 No. 1,1987FLUX-LIMITEDIRÁSGALAXIES171 F(60) ratiosareallhigherthanothergalaxiesofthesame60 (Fig. 10).Thusunobscurednuclearactivityisprobablynota in thesamerangeasnon-Seyfertgalaxiesoursample widths, [Om]/H/?(Baldwin,Phillips,andTerlevich1981),lies active galaxiesinoursamplearedistinctivethattheirF(25)/ sample. strong contributortothe60/unfluxingalaxiesour Their nuclearactivity,asmeasuredbytheratioofequivalent luminosities; theyrangefrom8x10Lto4- large overabundanceofactivegalacticnuclei(AGNs)inthis IR-bright sample. uncertainties intheclassificationscheme.Thusthereisnota COUNTS PER PIXEL 0 We notethattheinfraredspectralenergydistributionsof The Seyfertgalaxiesdonothaveextraordinarilyhigh60fim Fig. 6.—InfraredexcessL(60)/Lvs.60pimluminosity.ThesolidlineshowsthepositionofagalaxyM==—19.2;dashedlinesindicate dispersionin B © American Astronomical Society • Provided by the NASA Astrophysics Data System luminosities ofthesubsampleforwhichmorphologicaltypes are available.Notethatfewgalaxiesinoursamplehavetypes luminosity mightnotbeapparentwithinthelimitedrangeof luminous observed,andacorrelationbetweenshape which lackmorphologicalclassificationsareamongthemost correlation isapparent.However,thegalaxiesinoursample Types areplottedinFigure11asafunctionofluminosity.No fim luminosities(seeFig.4).Therelativelyhigh25/¿mfluxesof active galaxieshasbeennotedbyMiley,Neugebauer,and POSS platesforabout85%ofthegalaxiesinoursample. Soifer (1985). Morphological classificationscouldbeestimatedfromthe Fig. 8.—SpectrumofMK727,classified asanHnregiongalaxy d) Morphology \—IC/} o¿ 172 SMITH ET AL. Vol. 318 interacting groups. If emission from dust heated by recent is a major contributor to the far-infrared flux, these results are consistent with the suggestion by Larson and Tinsley (1978) that interactions between galaxies can trigger star-formation bursts. e) Space Distribution Comparing the space distribution of our sample with that of an optically selected sample, we find that the IRAS galaxies trace the cellular pattern of galaxies observed by de Lapperent, Geller, and Huchra (1986); however, a density enhancement in the core of Coma the size of the optical density enhancement is not observed. Defining the boundaries of Coma by 12h30m < a < 13h30m, 26?5 < <5 < 32?5, 5000 km s_1 10 L0 are found in multiple systems, and we find that 18% ± 5% of all of the An analysis of the colors and morphology of the galaxies in 11 our sample suggests that galaxies exceeding L(60) = 10 L0 galaxies in our sample are classified as peculiar or are in pairs 9 (see Table 3). This value is significantly higher than the fraction differ significantly from those having L(60) < 10 L0- The (6.4% ± 0.1%) of peculiar or paired galaxies found in an opti- eight high-luminosity galaxies have cally selected sample (Arp and Madore 1977). Lonsdale, F(12)/F(60) < 0.047 , Persson, Matthews (1984) found that an even larger fraction (37%) of the bright galaxies in the IRAS mini-survey were in 0.42 < F(60)/F(100) < 0.92 ,

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1987ApJ. . .318. .1613 tion ofinfrared-brightgalaxies, wefindthat(1)asimplepower Huchra etal.(1983). may beduetodifferencesintheproximityofdust the regions stillassociatedwithmolecular clouds. have ahigherfractionoftheir massconcentratedinHn seems plausible,forexample,thatgalaxiesofhighbluelumin- heating sourcesingalaxiesofdifferentblueluminosity. It highest amongthemostluminousinfraredgalaxies(Young et luminous infraredgalaxies.Thissuggestionisconsistent with osity mayhaveundergonearecentburstofstarformation, and al 1986). the hypothesisthatefficiencyofmassivestarformation is function mayreflectahigherlight-to-massratiointhemost constant light-to-massratioforgalaxies.Theexcessdensity of while theninelow-luminositygalaxieshave luminous infraredgalaxiesabovethatexpectedforaSchechter of primordialfluctuationsintheearlyuniverseandassumesa Schechter 1974)byanargumentinvolvingthemassspectrum luminosity extreme. A i-testshowsthatthesedistributionsdifferfromoneanother tion inthatnoexponentialcutoffisobservedatitshigh- luminosities, anddoesnotappeartofollowaSchechterfunc- other, associatedwithinteractingsystems,dominatesathigh galaxies areisolated.Thesefactssuggestthatthederivedinfra- Schechter functionanddominateatlowluminosities.The one, associatedwithnormalspirals,mayapproximatea red luminosityfunctionisasuperpositionoftwodistributions; galaxies areinmultiplesystems,whileallofthelow-luminosity No. 1,1987 at the98%confidencelevel.Atleasthalfofhigh-luminosity Fig. 11.—Morphologicaltypevs.60pimluminosity.ThescaleusedisthatdefinedbydeVaucouleursetal.(1976),andthetypesweretakenfrom thispaperand The lackofgalaxieslowblueluminosityinoursample The Schechterluminosityfunctionwasderived(Pressand In agreementwithpreviousstudies oftheluminosityfunc- © American Astronomical Society • Provided by the NASA Astrophysics Data System 0.23