University of Massachusetts Amherst ScholarWorks@UMass Amherst
Astronomy Department Faculty Publication Series Astronomy
1996 The global rate and efficiency of star formation in spiral galaxies as a function of morphology and environment Judith S. Young
Lori Allen
Jeffrey D.P. Kenney
Amy Lesser
Brooks Rownd
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Recommended Citation Young, Judith S.; Allen, Lori; Kenney, Jeffrey D.P.; Lesser, Amy; and Rownd, Brooks, "The global rate and efficiency of star formation in spiral galaxies as a function of morphology and environment" (1996). Astronomical Journal. 859. Retrieved from https://scholarworks.umass.edu/astro_faculty_pubs/859
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For more information, please contact [email protected]. 1996AJ 112.1903Y THE ASTRONOMICALJOURNAL lecular clouds,asisobservedintheMilkyWay,then mation perunitmassofmoleculargas,whichwealsocall important todeterminethemeanrateofhighmassstarfor- interest todeterminewhetherthedisksofgalaxiesdiffer- galaxies, itisnowwellknownthatmoleculargasfoundin which moleculargasisconvertedintostars.Amongspiral evolution ofthosegalaxiesislargelydrivenbytherateat phological typedependenceandtheenvironmentaldepen- both locatedinthedisk. changes asafunctionofmorphologicaltype(Boroson1981; along theHubblesequence.Thisapproachtostudyof the starformationefficiencyfordiskgalaxies ent Hubbletypesevolveatdifferentrates.Tothisend,itis all spiraltypes(cf.Young&Knezek1989),anditisofgreat Kent 1985)—sincethemolecularcloudsandyoungstarsare spiral galaxiesisindependentofbulgeluminosity—which department ofAstronomy,YaleUniversity, NewHaven,CT06511. dence ofthehighmassstarformationefficiencythrougha Honolulu, HI96822. Visiting JCMTFellow,Instituefor Astronomy, UniversityofHawaii, 1903 Astron.J.112 (5),November1996 If starformationinexternalgalaxiestakesplacemo- Previous studiesofgalaxieshaveaddressedboththemor- © American Astronomical Society • Provided by theNASA Astrophysics Data System Department ofPhysicsandAstronomyFiveCollegeRadioObservatory,UniversityMassachusetts,Amherst, brightness forspiralgalaxiesalongtheHubblesequence;Sd-IrexhibitameanHasurface Estimates forthetotalformationratehighmassstarshavebeencomparedwithglobalmoleculargas brightness 1.4timeshigherthantheSbc-Scdgalaxies,and2-3Sa-Sbgalaxies. mass starformationratesinthesegalaxies.WefindasmallbutsignificantvariationthemeanHasurface total fluxofcontinuum-subtractedHa:lineemission,andthereforethesurfacebrightnesseshigh CCD imagesofHa:andR-bandemissionin120spiralgalaxieswereobtainedusingthenow-retiredNo. morphological typeandenvironment.Wefindthatthemeanefficiencyofhighmassstarformationinthis masses todeterminetheglobalefficiencyofhighmassstarformationasafunction mean starformationefficiencyamongisolatedgalaxiesissignificantlylowerthanthatinteracting times higherthaninisolatedspiralgalaxies,uncorrectedforextinction.Thisconfirmspreviousfindings environments (i.e.,stronglyinteractingsystems)arefoundtohaveameanstarformationefficiency~4 Society. well tracedbyboththeHaandIRluminosityinspiralgalaxies.©1996AmericanAstronomical far-inffared luminosityratherthantheHatotracerateofhighmassstarformation,that Scd, althoughthereisawiderangeinstarformationefficiencieswithineachtype.Galaxiesdisturbed sample ofspiralgalaxiesshowslittledependenceonmorphologicaltypeforSathrough systems. Thisresultprovidesfurtherconfirmationthattherateofhighmassstarformationisreasonably (Young etal1986a,b;Sanders1986;Solomon&Sage1988;Tinney1990),basedonthe 1-0.9 mtelescopeofKittPeakNationalObservatory.Theseimageswereusedtoderivethedistributionand 12 Judith S.Young,LoriAllen,JeffreyD.P.Kenney,AmyLesser,andBrooksRownd THE GLOBALRATEANDEFFICIENCYOFSTARFORMATIONINSPIRALGALAXIES 1. INTRODUCTION AS AFUNCTIONOFMORPHOLOGYANDENVIRONMENT Received 1996January24;revisedJune24 Electronic mail:[email protected] VOLUME 112,NUMBER5 0004-6256/96/112(5)/1903/25/$ 10.00 Massachusetts 01003 ABSTRACT Wiklind &Henkel1989;DevereuxYoung1991).Differ- rals, anumberofinvestigatorshavefoundnoglobalvaria- Yerma 1986;Youngetal1989;Thronson tions inthemeanL(IR)/^#(H)withtype(Rengarajan& molecular gasmass[^#(H)].Forearly-andlate-typespi- comparison ofthefar-inffaredluminosity[L(IR)]with present rateofhighmassstarformationindiskgalaxies,as Tinney etal1990),indicatingthattheyieldofhighmass interacting galaxiesrelativetoisolatedspirals(Youngetal ences arefound,however,inthemeanL(IR)/L#(H)for far-inffared, wehaveundertakenaprogramtodeterminethe ratio oftheHaluminosityto massofmoleculargasisan proportional tothenumberof ionizingphotonsfromOB most ofthegalaxiesstudiedhere.BecausefluxinHais well asthestarformationrateperunitmassofmolecular the presenceofrecentlyformed highmassstars.Thus,the galaxies, sincetheIRASresolutionisinsufficienttoresolve determine thedistributionofhighmassstarformationwithin gas. Theprimaryincentiveforthisprogramwasoriginallyto stars perunitmassofmoleculargasininteractinggalaxiesis stars, intheabsenceofabsorption bydust,itdirectlytraces ~5 timeshigherthaninisolatedgalaxies. 1986a, 1986b;Sandersetal1986;Solomon&Sage1988; 2 2 2 Using theluminosityinHaasopposedtothat © 1996Am.Astron. Soc.1903 NOVEMBER 1996 1996AJ 112.1903Y independent indicatoroftheyieldhighmassstarsperunit paper, wewillexaminetheradialvariationsinrateofstar imaging programontheglobalhighmassstarformationrate mass ofmoleculargas,orthestarformationefficiency. based ontheiropticalorinfraredproperties,suchasthetotal Extragalactic COSurveycoverawiderangeinproperties, molecular gaswithinthesegalaxies. formation andtheyieldofhighmassstarsperunit the global100pmfluxdensity,Sjoq.Mostofgalaxiesin blue magnitude,theglobal60pmfluxdensity,S,or FCRAO ExtragalacticCOSurveywereselectedfromthe larger sampleofgalaxiesisnotcompleteinaflux-limited pair tocluster,andfromisolatedmergingsystems.The including lenticulars,spirals,andirregulars;galaxieswith Survey (Youngetal1995).Thegalaxiesincludedinthe Radio AstronomyObservatory(FCRAO)ExtragalacticCO an examinationofthehighmassstarformationefficiencyin a comparisonofinteractingandisolatedgalaxies,aswell and efficiencyinasampleof120spiralgalaxies.Weinclude magnitudes, heliocentricvelocities,distances,andopticaldi- 5ioo>10 Jy(fromcoaddedIRASdata).Thegalaxieswhich following threecriteria:(1)5®<13.0,(2)5>5Jy,or(3) the COSurveyarespiralorirregulargalaxieswhichhave RC2 (deVaucouleursetal.1976)ortheIRASdatabase optical diametersbetween4and100kpc;environmentsfrom spiral galaxiesofdifferentmorphologicaltypes.Inalater merger remnantsbasedonthepresenceoftidaltailsorother are includedinthisCCDimagingprogramlistedTable declinations northof—25°andsatisfyatleastonethe members included inthisimagingstudy. the morphologicaltypedistribution fortheVirgoCluster ions within1Mpconthesky,4 areinloosegroups,and43 collisions (Schweizeretal.1983;Joseph&Wright1985; morphological peculiaritieswhichcanresultfromgalaxy of roughlyequalsize,andninesystemswhichwerefertoas galaxies isshowninFig.1.Theincludedthis galaxies oftypeS0-Sab,44Sb-Sbc,20gal- ameters. space. Themajorityofthegalaxiesobservedaspart served wereselectedtospanawiderangeofparameter sense, noritisvolumelimited,butratherthegalaxiesob- are membersoftheVirgoCluster. Figure1alsoillustrates spirals therearesixclosepairsinwhichthetwogalaxies study arefoundinawiderangeofenvironments.Amongthe and 2Peculiars.Themorphologicaltypedistributionofthese axies oftypeSc,18galaxiesScd-Sdm,8Irregulars, 1904 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES Sanders etal.1986).Attheother extremeofenvironment, 120 ofthe300galaxiesobservedaspartFiveCollege 10 galaxiesaresoisolatedthatthere arenomassivecompan- 1, alongwiththeircoordinates,morphologicaltypes,blue 60 60 In thispaper,wepresentinitialresultsfromourCCD We haveobtainedHaandredcontinuumCCDimagesfor The 120galaxieswhichwereimagedinHainclude25 © American Astronomical Society • Provided by theNASA Astrophysics Data System 2.1 GalaxySample 2. THEHaDATA produce ascaleofeither0.77"or0.86"perpixel,depending mary oftheobservationsisgiveninTable2,including on theparticularCCD.Theareaimagedwaseither6'by CCD directimagingsystemonphotometricnightsbetween by lessthan5%forwavelengthswithin±20Aofthepeak, dard StarManual(Barnes&Hayes1984).Theairmassof in Ha.Airmasscorrectionsweremadeusingthestandard of thetargetgalaxy,andeitherabroad7?-bandfilter(X each CCD. CCD usedtoimageeachgalaxy,andthecharacteristicsof or 7'by4',alsodependingontheparticularCCD.Asum- KPNO (/7.5)witheithertheT12,T13,RCA3,orTEK1 the observations,specificHainterferencefiltersused, extinction curveforKittPeakgivenintheKPNO1RSStan- gration timesweretypically5-10minintheRbandand1h AX=380 A)todeterminethenearbycontinuumlevel.Inte- serving eachgalaxythroughtwofilters:anarrow(AX morphological type. trates theR-bandandcontinuum-freeHa+[Nn]emissionin of theHa+[Nn]emission.Figure2(Plates85-90)illus- the interferencefilterimagestoyieldcontinuum-free interference filterimagesusing~5unsaturatedforeground to subtracttheskyemissionfromeachimage.Then, next stepinobtainingcontinuum-freeHa+[Nn]imageswas Camera forthe#1-0.9mTelescope.”Afterflatfielding, was reducedby~5%-10%,andinthesecasesatransmis- midway betweentheavailablefilterswheretransmission the galaxies.Inafewcases,velocityofgalaxywas filters werecharacterizedbytransmissionwhichdecreased able tousbythestaffatKPNO.MostofHainterference characteristics asafunctionofwavelengthweremadeavail- the imagingobservations.Foreachfilter,transmission gration timesaregiveninTable2. characteristics ofthesefilters,andtheHaR-bandinte- procedure consisted ofremovingincompletely subtracted determined fromtheKPNO 1RS StandardStarManual more oftheCCDphotometric standardsG191B2B,Feige calibrated usingobservationsfromthesamenightofoneor a subsetofthegalaxiesinoursamplecoveringrange continuum imageswereregisteredandscaledrelativetothe sample, sixdifferentHainterferencefilterswereneededfor stars, andthescaledcontinuumimagesweresubtractedfrom scribed bySchoening(1987)inthe“CCDDirectImaging sion correctionwasappliedtotheimage. such thattheredshiftedHalinewasinauspiciouslylocated so thatnotransmissioncorrectionswereneededformostof standard usedforeachgalaxy; fluxes forthesesourceswere 1986 Octoberand1989April.TheCCDswereoperatedto 120 galaxiesusingthenow-retiredNo.1-0.9mtelescopeof (Barnes &Hayes1984).Thefinal stepinthedatareduction =76-86 A)interferencefiltercenteredonHaatthevelocity =6470 A,AX=1110A)oranarrowRfilter(X=7024 110, HZ44,andBD+8°2015. Table2liststhecalibration Measurements oftheHa+[Nn]emissionweremadefor The Ha+[Nn]emissionlinefluxeswereobtainedbyob- The imageswerebiassubtractedandflatfieldedasde- Because oftherangeinredshiftsforgalaxiesour The continuum-subtractedHa+[Nn]imageswereflux 2.2 ImagingObservations 1904 1996AJ 112.1903Y 1905 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System NGC278 NGC253 NGC488 NGC157 NGC 925 NGC 891 NGC 660 NGC628 NGC 520 NGC 1087 NGC 1084 NGC 1055 NGC 972 NGC 2146 NGC 1961 NGC 1614 NGC 1068 NGC 2683 NGC 2336 NGC 2276 NGC 1569 NGC 2798 NGC 2775 NGC 2339 NGC 3310 NGC 3077 NGC 3034 NGC 2976 NGC 2903 NGC 2841 NGC 3521 NGC 3504 NGC 3351 NGC 3184 NGC 3147 NGC 3079 NGC 4038 NGC 3810 NGC 3718 NGC 3690 NGC 3675 NGC 3631 NGC 3627 NGC 3623 NGC 3593 NGC 3556 NGC 4064 NGC 4041 IC 694 NGC 4212 NGC 4194 NGC 4192 NGC 4189 NGC 4178 NGC 4157 NGC 4102 NGC 4088 NGC 4237 NGC 4216 NGC 4206 Galaxy (1) 00 4914.8 00 4507.8 00 3214.4 02 1925.2 01 4020.7 01 3400.7 01 2159.4 01 19\\2 02 4006.5 02 3910.7 02 3116.6 02 2416.6 06 1040.1 05 3633.9 04 3136.0 04 2605.8 02 4351.6 02 4331.8 09 0741.0 08 4934.8 07 0525.1 07 1828.0 09 51453 09 4310.0 09 2919.9 09 1834.9 09 14093 07 1022.0 09 5835.4 09 5921.9 11 2324.2 11 0836.8 11 0315.1 10 4119.6 10 1239.3 11 3823.5 11 2950.7 11 2541.8 1125 44.2 11 1813.2 1100 28.1 10 3540.3 10 1517.7 12 0137.3 11 5919.2 11 1737.9 11 1618.6 11 592 12 0351.6 12 0303.1 11 5938.7 12 14383 12 1306.4 12 1141.7 12 1115.4 12 1113.9 12 1013.1 12 0834.6 12 13203 12 43.7 a(1950) h ms (2) +42 0718 +47 1643 +13 2332 +15 3155 +04 5936 +80 1635 +78 2223 +69 2116 +64 4418 +0013 45 +29 0535 +33 2120 +03 3213 +07 1435 +33 3623 +18 5142 +85 5058 +11 4455 +53 2033 +43 5136 +53 2643 +69 5511 +21 4319 +51 1119 +42 1237 +18 4316 +54 4821 +50 4551 +52 5923 +50 4913 +58 5000 +58 5023 +53 45 +41 4028 +55 5511 +68 5833 +68 0843 +13 1810 +15 1023 +13 4217 +1108 30 +62 2503 +13 0528 +28 1435 +11 5800 +73 3902 +15 3608 +13 2538 +14 1045 +13 2200 +55 5633 +00 1358 +13 1608 -25 3342 -08 4018 -07 4706 -00 1332 -08 4054 -00 4219 -18 3506 5(1950) o »n (3) Table 1.Galaxyproperties. Pec SAB(s)c 10 SAB(rs)b SAB(rs)bc IBm SA(s)b sp SB(s)a pec SA(s)c SA(r)b SA(s)c (R)SA(is)b SBb sp SAB(s)d SAB(rs)c SB(s)c pec SAB(rs)c SAB(rs)bc SAB(r)bc SAB(rs)c SB(s)ab pec IBm pec SA(s)b SA(s)c 10 pec 10 sp SAB(rs)bc SA(r)b SA(r)ab SA(rs)b IBm pec SA(rs)bc SB(s)m pec SA(rs)c SB(s)a pec SAc pec SB(s)a pec SAbc SB(rs)dm SAB(s)b sp SAB(s)b SAB(rs)bc SB(s)a pec SBm pec SAB(r)bc pec SAB(rs)cd SA(rs)bc SB(s)c sp SAB(s)b SA(s)bc SAB(s)ab SAB(rs)cd SB(r)b SAB(rs)bc SAB(rs)a SA(s)0/a SB(s)cd sp SAB(rs)bc (R)SAB(s)ab SAB(s)b Type (4) 10.88 10.94 10.80 11.90 10.49 10.76 1235 1039 11.18 11.91 10.60 11.71 11.43 11.98 1134 13.10 1236 11.38 1036 10.67 12.28 11.55 10.83 10.96 10.79 11.53 10.03 10.58 11.11 10.49 11.44 10.52 11.15 13.15 10.73 11.54 1038 10.32 12.43 10.85 10.90 11.07 10.43 11.24 10.00 11.52 10.18 10.18 (5) 7.40 9.48 9.83 9.17 9.84 9.05 938 9.26 8.72 9.26 9.59 (km/sec) V 2999 2528 3115 2027 2097 1191 1658 1014 1167 1026 -129 701 742 973 sun 945 297 825 896 701 2168 2180 4745 2199 2423 2369 3890 1657 2721 1824 1413 1109 1050 1532 1708 1135 1137 1529 (6) 642 249 655 560 856 524 838 15 284 246 652 569 660 685 994 589 697 780 815 807 -87 42 10 (Mpc) 62.1 24.9 4.57 20.0 535 20.0 9.55 26.4 2.82 28.9 2.58 21.9 8.71 62.1 20.0 239 20.0 8.32 20.0 3.02 20.0 2.45 20.0 5.01 20.0 4.47 52.6 2.45 Dist. 14.7 5.89 19.7 3.16 17.2 4.27 18.1 6.92 16.4 5.75 (7) 45.4 45.8 213 35.0 47.8 92.9 28.1 22.7 33.4 46.7 20.6 36.9 51.6 81.1 19.6 17.7 243 343 14.3 14.1 15.9 29.6 21.3 57.6 14.0 193 11.9 12.8 13.5 10.9 15.4 33 4.7 4.8 9.3 33 3.5 3.3 6.7 6.7 2.40 1.17 25.12 1033 13.49 1132 12.59 10.00 437 4.79 2.19 4.27 739 9.77 9,12 535 6.92 6.03 2.88 2.88 3.63 4.47 6.92 2.63 3.47 (8) 4.90 2.75 437 2.75 933 739 o 9.55 2.69 7.41 6.92 3.98 8.13 1.32 3.63 8.71 5.75 8.32 25 433 25.2 26.0 21.7 21.7 21.4 553 21.1 48.4 29.1 273 33.1 363 30.5 37.5 55.6 18.1 13.3 17.6 14.3 (kpc) Ref. 100.8 ^25 43.4 473 45.7 40.7 633 24.1 47.6 70.0 55.4 52.0 c,d 37.2 23.6 35.3 (9) GO) 96.2 35.7 393 36.1 25.1 373 11.3 27.3 23.9 66.7 34.2 33.1 23.1 29.0 22.4 37.4 35.6 53.5 13.1 10.8 17.0 19.5 18.2 3.9 4.4 5.0 c f c,
Notes to Table 1
^0 *See Young et al (1995) for alternate references. UD (T\ Col. (1) Galaxy name—NGC, IC, Mrk, or Aip designation. Col. (2)-(3) Right Ascension and Declination (1950.0 coordinates) from Dressel and Condon (1976), unless alternate reference ‘a’ is noted in Column (10). Col. (4) Morphological type from RC2, unless alternate reference ‘b’ is noted in Column (10). Col. (5) Total blue magnitude, Bx°, corrected for galactic and internal absorption from RC2, unless alternate reference ‘c’ is noted in Column (10). Col. (6) Heliocentric velocity from RC2, unless alternate reference £d’ is noted in Column (10). Col. (7) Distance to the galaxy. For most galaxies, the distance was calculated from the Hubble Law after applying the solar motion correction to the velocity -1 -1 (RC2, column 29), and using Ho=50 km s Mpc . The exceptions include a small number of nearby galaxies for which the alternate reference ‘e’ is noted in Column (10), and Virgo cluster members, assumed to be located at a distance of 20.0 Mpc [see alternate reference ‘f in Column (10)]. Col. (8) Optical angular diameter measured in arcminutes out to the 25 mag arcsec-2 isophote from RC2, unless alternate reference ‘g’ is noted in Column (10). Col. (9) Linear diameter in kiloparsecs, calculated using Columns (7) and (8). Col. (10) Alternate References: a=Coordinates from RC2, Lonsdale et al. (1985), Sanders et al. (1986), Tacconi and Young (1987), Bothun et al. (1989), Giovanelli and Haynes (1989), or Goldsmith and Young (1989). b=Morphological type from UGC or Tully (1988). c=Bt from UGC and corrected for galactic and internal absorption as in RC2, or Bx° from de Vaucouleurs, de Vaucouleurs and Buta (1981) or Tacconi and Young (1987). d=Heliocentric velocity from Huchtmeier et al. (1983), Tully (1988), Thronson et al (1989), or Bothun et al. (1989). e=For nearby galaxies, distances are not derived from the Hubble Law. These distances are from Rogstad and Shostak (1972), Sandage and Tammann (1975), Bosma et al (1977), Hunter, Gallagher, and Rautenkranz (1982), Tacconi and Young (1985, 1987), Thronson et al (1989), or Young et al. (1989). f=Galaxies in the Virgo cluster are taken to be at a distance of 20.0 Mpc, following Kenney and Young (1988). g=D25 from UGC, Tully (1988), Tacconi and Young (1987), or Bothun et al (1989).
foreground stars and cosmic rays from the flux-calibrated filters are —80 A wide and therefore include the satellite images, using IRAF. Calibrated Ha+[N ll] emission line [N n] lines at XX 6548,6584, (2) determination of the con- fluxes were determined over the area in which HII regions tinuum level to subtract from the observed Ha interference were detected in each image. Table 2 lists the observed Ha filter image, (3) absolute calibration uncertainties, and (4) +[N ll] fluxes for the program galaxies. extinction, both Galactic and internal to the galaxies them- selves. Additionally, some Ha emission could arise from an 2.3 Sources of Uncertainty in Ha Fluxes active nucleus, as opposed to on-going star formation. Each Possible sources of error in the Ha fluxes include (1) of these possibilities will be discussed in turn in this section. contamination by [N n] emission, since the Ha interference 2.3.1 [Nil] emission 60 The [N n]/Ha ratio is likely to be high in the nuclei of spiral galaxies where Ha absorption is strongest and [N ll] is in emission (Rubin & Ford 1986). However, the galaxies in our sample are not as nearby as M31 and M33, and Rubin & Ford (1986) show that the nuclear Ha absorption is over- ctiK 40 shadowed by disk Ha emission in more distant galaxies ob- served with a fixed aperture. Indeed, Kennicutt & Kent (1983) find that nuclear [N n] emission rarely dominates the o integrated photometry of spiral galaxies. They also find, u
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1903Y 1908 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System NGC157 NGC 1087 NGC 1068 NGC 1055 NGC972 NGC925 NGC891 NGC660 NGC628 NGC520 NGC488 NGC278 NGC253 NGC 2339 NGC 2336 NGC 2146 NGC 1961 NGC 1614 NGC 1569 NGC 1084 NGC 3077 NGC 2798/9 NGC 2775 NGC 2683 NGC 2276 NGC 3147 NGC 3079 NGC 3034 NGC 2976 NGC 2903 NGC 2841 NGC 3623 NGC 3593 NGC 3521 NGC 3351 NGC 3627 NGC 3556 NGC 3504 NGC 3310 NGC 3184 NGC 3631 NGC 4102 NGC 4041 NGC 4038/9 NGC 3690/ NGC 3675 NGC 4088 NGC 4064 NGC 3810 NGC 3718 NGC 4216 NGC 4212 NGC 4206 NGC 4194 NGC 4192 NGC 4189 NGC 4178 NGC 4157 NGC 4237 IC 694 Galaxy Obs.DateCCD (1) 02/25/89 02/26/89 03/26/88 03/23/87 02/27/89 02/27/89 12/09/87 10/25/86 12/12/87 12/11/87 12/03/88 12/01/88 10/26/86 12/03/88 12/03/88 12/01/88 12/09/87 12/11/87 12/03/88 12/01/88 10/25/86 12/10/87 12/10/87 02/27/89 12/02/88 10/25/86 12/01/88 12/03/88 12/03/88 12/12/87 03/23/87 04/01/89 12/11/87 12/11/87 12/08/87 12/11/87 12/08/87 10/26/86 12/01/88 12/02/88 03/22/87 04/02/89 03/31/89 03/26/88 02/27/89 12/10/87 12/09/87 12/03/88 03/30/89 04/01/89 12/09/87 12/03/88 12/11/87 12/02/88 . (2) 12/12/87 12/10/87 12/12/87 12/11/87 12/12/87 (m/d/yr) RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 RCA3 TEK1 TEK1 TEK1 RCA3 RCA3 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TI3 712 TI3 TI3 TI2 TI3 TI2 TI2 TI3 TI3 TI3 TI3 TI3 TI3 TI3 TI2 TT2 TI3 TI3 TI3 TI3 TI2 TI3 TI3 (3) TI3 TI3 TI3 TI3 TI2 TI2 TI3 TI2 Airmass 1.14 1.07 1.86 1.35 1.85 1.01 1.05 1.07 1.05 1.17 130 1.32 130 137 Table 2.Observationalparameters. 1.08 1.58 1.71 1.46 1.36 1.34 1.19 1.40 1.58 131 1.42 134 1.06 1.06 1.43 1.08 1.08 1.19 1.40 1.08 130 135 1.35 1.61 1.12 1.44 1.12 1.35 1.38 1.61 1.38 1.14 1.38 1.24 1.68 1.12 1.05 1.26 1.49 1.60 135 1.77 1.14 1.88 1.64 (4) R 2000 * 1100' Image Airmass 1500 * 1300 * 3000** 3300* (sec) 450 400 200 200 600 500 300 300 300 900 300 300 500 300 450 200 450 200 300 300 300 300 300 170 750 200 300 100 125 420 400 450 420 420 450 200 100 420 300 120 300 300 300 100 150 250 300 180 150 125 (5) (6) 40* R Ha 70 80 235 138 1.04 1.18 1.15 1.07 1.04 1.05 1.08 1.90 1.37 134 131 1.20 135 1.55 1.70 1.45 1.32 131 1.05 1.07 1.04 1.35 1.12 1.34 1.08 1.35 1.46 138 139 1.24 1.06 1.12 138 133 1.41 130 1.11 1.39 139 1.10 1.21 1.61 1.35 1.15 1.46 1.28 1.25 1.08 137 1.52 1.10 1.09 1.59 1.20 1.44 1.30 1.22 4000 4000 4500 2000 2500 3600 2700 2500 3000 3000 4500 2700 3000 3600 5000 (sec) 4100 3000 3600 4000 4500 2500 3000 2000 3000 3600 1800 1600 2500 3600 1000 5000 1200 1900 1800 1200 1800 1400 Ha (7) 750 300 4000 4500 4500 4000 4000 3000 3000 3000 4000 3300 3000 3600 2500 3000 3900 1500 1250 80 600 600 Filter Ha (8) BD+82015 Feige 110 Calibrator logF(Ha) Feige HO Feige HO Feige HO Feige HO Feige HO Feige 110 G191B2B Feige HO Feige 110 Feige 110 G191B2B G191B2B G191B2B Feige HO G191B2B G191B2B G191B2B G191B2B G191B2B Feige HO Feige HO Feige 110 Feige 110 Feige 110 Feige 110 Feige 110 G191B2B G191B2B G191B2B G191B2B G191B2B Feige 110 Feige 110 Feige 110 G191B2B G191B2B G191B2B G191B2B BD+82015 BD+82015 Feige HO Feige 110 Feige 110 Feige 110 Feige 110 Feige HO G191B2B G191B2B Feige 110 Feige 110 G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B (9) 2 (erg/cm/s) -11.11 -11.64 -1239 -11.17 -10.19 -11.51 -11.68 -10.91 -12.40 -10.64 -1034 -12.03 -11.10 -11.02 -1136 -1137 -1132 -11.84 -1136 -11.14 -11.04 -11.67 -1133 -11^5 -1132 -11.42 -11.63 -11.09 -11.81 -11.47 -10.04 -10.67 -10.81 -10.81 -11.12 -10.75 -11.43 -11.73 -1131 -11.40 GO) -11.15 -11.13 -12.11 -12.54 -11.09 -1131 -11.59 -11.72 -11.17 -11.25 -10.79 -11.70 -11.43 -11.90 -11.59 -12.15 -11.52 -11.73 -12.04 1908 1996AJ 112.1903Y 1909 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System NGC4254 NGC 4293 NGC 4303 NGC 4299 NGC 4298/ NGC4294 NGC 4351 NGC 4321 NGC 4419 NGC 4413 NGC 4394 NGC 4380 NGC 4450 NGC 4438 NGC 4424 NGC 4535 NGC 4527 NGC 4522 NGC 4519 NGC 4501 NGC 4498 NGC 4459 NGC 4536 NGC 4532 NGC 4526 NGC 4639 NGC 4579 NGC 4567/8 NGC 4561 NGC 4548 NGC 4654 NGC 4651 NGC 4647 NGC 4571 NGC 4569 NGC 4713 NGC 4710 NGC 4689 NGC 4808 NGC 4736 NGC 5248 NGC 5005 NGC 4826 NGC 6240 NGC 5907 NGC 5194 NGC 6946 NGC 5631 NGC 7541 NGC 7479 NGC 7331 NGC 7217 NGC 6951 NGC 6643 NGC 7625 IC 342 Arp 220 Mile 231 IC 356 NGC 4302 Galaxy (1) Obs. Date 03/31/89 03/25/88 03/24/87 03/31/89 03/31/89 03/29/88 03/30/89 03/30/89 04/01/89 03/24/87 04/01/89 04/02/89 03/26/87 03/26/88 03/30/89 04/02/89 03/30/89 03/25/87 04/02/89 03/29/88 04/01/89 03/26/87 03/29/88 03/29/88 03/26/88 03/25/88 03/26/88 03/23/87 03/25/88 03/31/89 03/26/87 03/26/87 03/23/87 03/30/89 03/31/89 03/29/88 03/30/88 03/26/87 03/25/87 02/27/89 03/23/87 02/27/89 02/26/89 02/27/89 03/29/88 03/30/88 04/02/89 03/30/88 03/25/88 03/30/88 (m/d/yr) 12/02/88 10/25/86 12/10/87 12/01/88 12/03/88 12/01/88 10/26/86 12/08/87 12/02/88 (2) TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 TEK1 CCD R RCA3 TEK1 RCA3 RCA3 TEK1 RCA3 RCA3 TEK1 TEK1 TEK1 TEK1 TEK1 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 (3) TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI2 TI3 TI2 TI3 Airmass 1.17 1.31 1.07 U6 1.25 1.30 1.10 1.08 1.84 2.14 2.01 1.05 1.40 1.83 1.07 1.16 1.06 1.06 1.03 1.05 129 1.67 123 123 1.16 1.89 1.25 1.06 (4) 1.07 1.09 1.15 123 1.13 1.51 1.66 1.36 1.06 1.01 1.20 125 1.18 1.17 1.50 1.10 1.10 126 1.39 1.44 127 1.07 1.18 1.08 1.03 133 1.05 120 128 127 1.11 Table 2.(continued) 11 1000 ^ 2500’' 2500" 2000" 1500 * 1000 1200 420 420 420 420 200 300 420 420 420 420 600* 900 900 420 420 400 450 * 250 420 250 300 900 600 (sec) 420 500 300 900 * 250 300 500 350 450 400 800 300 300 120 300 300 900 300 300 150 300 300 120 120 100 150 150 100 (5) 90 Airmass 1.32 1.21 1.17 Ha 1.59 1.16 1.17 1.06 1.09 1.13 1.08 1.05 1.11 1.28 1.61 1.11 1.50 1.70 1.43 1.15 (6) 226 1.12 1.06 1.45 1.46 1.15 122 1.17 1.10 1.40 1.31 1.06 1.05 1.11 1.74 1.68 1.87 122 1.12 129 1.02 1.07 127 1.11 1.16 1.38 1.38 1.36 1.31 1.12 1.39 1.31 1.06 1.17 1.14 1.10 1.06 1.19 129 1.29 Image Filter 4000 (sec) 4000 4000 4000 2000 4000 3600 3000 2000 4000 4500 4000 4000 3000 3000 2000 3000 3600 1200 4000 4000 Ha 4000 2500 2500 2000 4000 4500 6600 2700 4000 4000 3600 4000 2500 4000 3000 (7) (8) 3800 3000 4200 4500 5900 3600 1500 2500 3600 3000 1500 1850 1500 1500 5400 1500 1500 1500 1800 1800 600 800 300 BD+82015 BD+82015 Calibrator logF(Ha) G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B BD+82015 G191B2B G191B2B G191B2B G191B2B BD+82015 G191B2B G191B2B G191B2B G191B2B BD+82015 BD+82015 G191B2B G191B2B BD+82015 G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B G191B2B Feige 110 Feige 110 Feige 110 G191B2B G191B2B G191B2B Feige 110 Feige 110 G191B2B G191B2B G191B2B G191B2B G191B2B HZ44 HZ44 HZ44 HZ44 HZ44 (9) (erg/cm /s) <-17.00 -11.71 -11.92 -10.89 -11.74 -10.66 -11.62 -12.28 -12.43 -11.09 -11.97 -11.28 -12.29 -12.10 -11.81 -12.16 -11.34 -11.35 -1123 -12.18 -11.38 -11.98 -12.07 -11.26 -11.14 -12.02 -12.39 -11.63 -11.91 -11.24 -11.74 -11.52 -11.39 -11.84 -11.50 -11.62 -11.67 -11.79 -11.49 -11.08 -11.15 -10.33 -11.63 -10.27 -11.38 -10.47 -11.64 -11.48 -11.41 -11.10 -11.66 -11.67 -12.70 -11.76 -11.60 -11.57 -11.73 -10.93 -11.83 (10) 1909 1996AJ 112.1903Y 4KxX 04KxX -2-1 Col. (3)CCDusedfortheobservationsonnow-retired#1-0.9mtelescopeatKPNO.TheTICCDswereoperatedina2X2pixel-summedmode. CCD characteristicsareasfollows: Col. (2)Dateoftheimagingobservations. Col. (1)Galaxyname—NGC,IC,Mrk,orArpdesignation. 1910 used toimagethecontinuum,Khasavalueof0.073;galaxiesforwhichthisiscasehavelongerR-bandintegrationtimesandareindicatedwithan given by10°-,wherexistheairmassandKextinctionatwavelengthX.standardcurveforKittPeak(BarnesHayes central wavelengthof7024Aandawidth380A.ForNGC4212,indicatedbydoubleasterisk(**),thecontinuumwasobservedthroughfilter Longer integrationsweremadeusingananowR-bandfilterforsomegalaxies,indicatedbyanasteriskfollowingthetime.Thenarrowhas Col. (4)TheairmassoftheobservationsmadeusingR-bandfilter.correctionusedaspartfluxcalibrationimageis indicated asHc*-6inthenotetoColumn(8). Col. (5)Integrationtime,inseconds,fortheR-bandcontinuumimage.Thebroadfilterhasacentralwavelengthof6470Aandwidth1110A. asterisk incolumn5. of thefilter.IndividualvaluesKaregivenforeachHafilterinnotetocolumn(8). is givenby10,wherextheairmassandKextinctionatwavelengthXstandardcurveforKittPeak(BarnesHayes Col. (6)TheairmassoftheobservationsmadeusingHainterferencefilter.correctionusedaspartfluxcalibrationimage Col. (8)TheHafiltersusedfortheimagingobservationsdependonvelocityofgalaxy,andincludefollowing: Col. (7)Integrationtime,inseconds,fortheHainterferencefilterimage. 1984). ForthebroadR-bandfilterusedformostofcontinuumobservations,Khasavalue0.101.galaxiesinwhichnarrowwas 1984). FortheHainterferencefiltersusedforimagingobservations,Khasavaluerangingbetween0.095and0.082dependingoncentralwavelength listed isthatforbothgalaxies.Forthegalaxieswithlargestangularsizes(i.e.,NGC253andIC342),fluxesareinner6’regiononly. estimated tobe-20%.Forthegalaxypairs—NGC2798/2799,Arp299(NGC3690/IC694),NGC4038/4039,4298/4302,4567/4568—theflux Manual ofBarnesandHayes(1984). Col. (9)StandardstarusedforfluxcalibrationoftheHaandR-bandcontinuumemission.FluxesweredeterminedfromKPNO1RSStar Col. (10)LogarithmoftheobservedHa+[NII]fluxinunitsergcms.Nocorrectionsforextinctionhavebeenmade.TheuncertaintyF(Ha)is only theredcontinuum,butalso—7%ofHalineemis- interference filters.Thus,thecontinuumfilterdetectsnot terference filterimage,thereisaslightoversubtractionofthe result, whenthecontinuumimageissubtractedfromin- sion whichisdetectedintheinterferencefilterimages.Asa and atransmissivityatHawhichissimilartothatofthe x x line emission.However,thisoversubtractionofthe the globalHaflux,asdiscussed below. continuum level,whichcanleadtoa±20%uncertaintyin larger sourceofuncertaintyistheactualdetermination in thefirstplace,sonocorrectionforthiseffectwasmade.A emission willtendtobalancethepresenceof[Nll]lines x x cause asinglescale factorisappliedtothecontinuum image. x ence filterimagecanintroduce anerrorintheHaflux,be- x Determination ofthecontinuum levelintheHainterfer- © American Astronomical Society • Provided by theNASA Astrophysics Data System YOUNG ETAL.:STARFORMATIONINSPIRALGALAXIES 2.3.2 Determinationofthecontinuumlevel TI2 TEK1 TI3 CCD RCA3 filter Ha Wavelength Central 6693 6563 6744 6649 6608 6826 Number ofPixels (A) 396X396 396X396 512X512 508X320 Notes toTable2 Width Filter (A) 80 81 70 76 80 86 upon itistoobtainaspectrumateverylocationanddeter- that thereisa±5%errorinthedeterminationofcon- mine thecontinuumlevelateverypixel.)Ingeneral,wefind tinuum level,whichcanleadtoanuncertaintyofup we findthatthecalibrationmeasurements arerepeatablewith pends ontherepeatabilityofindividualstandardstarmea- tended emission. (While thisisnottheidealsituation,onlywaytoimprove bration is±5%.Alloftheobservations presentedherewere high accuracy,andthattheuncertainty intheabsolutecali- standard starsatdifferentairmasses andondifferentnights, standard extinctioncurve.From observationsofthesame surements andtheairmasscorrectionbasedonKittPeak taken onphotometric nights. ±20% intheglobalHafluxforlowsurfacebrightnessex- Pixel Scale 0.867pixel 0.777pixel 0.867pixel 0.867pixel The absolutecalibrationoftheemissionlineimagesde- Velocity Range 12,022±1828 8274±1965 5942±1850 3880±1580 1965 ±1590 (km/sec) 0±1600 2.3.3 Absolutecalibration 7.3 ’(E-W)X4.6’(N-S) 5.7’X5.7’ 5.7’X2.7’ 6.6’X6.6’ Field Coefficient Extinction 0.089 0.093 0.095 0.082 0.087 0.091 Kv 1910 1996AJ 112.1903Y been madefortheentiresample,Kennicutt&Kent(1983) is typically~1mag.ThisindicatesthattheHafluxesand to theHaluminositieslistedinTable3(seeSec.3.1).Al- be higherforgalaxieswhicharemorehighlyinclinedtothe rived ratesofhighmassstarformation. luminosities wemeasurearelowerlimitstotheintrinsicHa though nocorrectionforextinctionwithinthegalaxieshas for Galacticextinction,butthatcorrectionhasbeenapplied NGC 520,660,1068,2146,andM82. inclinations asafunctionofmorphologicaltypeforthegal- line ofsight.InFig.3,weshowthedistributiongalaxy fluxes andluminosities,thereforelowerlimitstothede- Extinction mapsderivedinthiswayfortheheavilyobscured in asampleof8compactHnregions(Dennefeld&Stasin- These correctionsarebasedonnear-IRimagingof[Sm] the mostheavilyreddenedgalaxiesinpresentsample: of thegalaxiesinourstudyhaveinclinationslessthan70°, axies wehaveimagedinHa.Thisfigureillustratesthatmost suggest thattheextinctionwithingalaxiesintheirsample tinction wasderivedfromthe[Sm]/Haratio,conservatively although awiderangeofinclinationswasincluded. here donotincludetheextinctioncorrectionsforNGC520, from GalactictoMagellanicmetallicity),withadispersionof tio dependsonmetalabundance(varyingbyafactorof—3 metallicity. Walleretal.(1992)findthattheunreddenedra- of afactor~2intemperatureanddensity—10 corrections whichrangefromafactorof1.7inNGC1068to central regionsofthesefivegalaxiesleadtoglobalextinction [S mj/Haratiois0.4inOrion(Lesteretal.1979)and0.33 assuming anintrinsic(unreddened)ratioof0.5;the X9532, whichsufferslessextinctionthandoestheHa by Kennicutt&Kent(1983;hereafter KK)andKennicutt dened [Sm]/Haratioisapproximatelyconstantoverarange etal. 1975). a factorof26inNGC520,consistentwithindependentmea- [S m]/Haratiomayresultinunderestimatingtheextinction. tometry, while the K87fluxeswereobtained from images the Hafluxesmeasuredbyuswith thoseofKKandK87for ouse 1987;Pogge&Eskridge1987),thelargestofwhichare 660, 1068,2146,andM82exceptwherenoted. only 25%foragivenmetalabundance.Theresultspresented surements oftheextinctionincentralregions(Benvenuti ska 1985).Thus,theadoptedvalueof0.5forunreddened (Waller etal.1988;Young1988).Theamountofex- 1911 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES measurements weremadeusing largeaperture(1'to7')pho- the 45galaxiesincommonbetween thesesamples.TheKK galaxies (Cohen1976;BagnuoloHuchra1977;Bush- et al.(1987;hereafterK87).Figure 4showsacomparisonof The ViafluxeslistedinTable2havenotbeencorrected We havederivedinternalextinctioncorrectionsforfiveof The extinctionoftheHaemissioninagalaxywilltendto Calculations byRubin(1988)indicatethattheunred- There areseveralpublishedsurveysofHaemissionin © American Astronomical Society • Provided by theNASA Astrophysics Data System 2.4 ComparisonwithHaFluxesintheLiterature 2.3.4 Extinction -2-1 0 4AHa) 20 -2 _1 taken witheitheravideocameraorCCD.Allofthemea- Ha luminosityisgivenby used toderiveHaluminositiesfortheprogramgalaxies.The individual fluxes. consistent atalevelwhichiswithintheuncertaintiesin other studiesis1.2±0.2.Thisindicatesthatthedatasetsare pressed insolarluminositiesisgivenby is theGalacticlatitudeofgalaxy;parameterCinEq. tion inourGalaxy.Thisextinction,magnitudes,isas- Ha fluxlistedinTable2,andCisthecorrectionforextinc- [N n]lines. Table 3. where Disthedistancetogalaxy,/(Ha)observed surements weremadewithfilterswhichalsoincludethe relevant detailsisincludedhere.TheCOobservationswere between 1980Novemberand1992November.Atthefre- telescope oftheFiveCollegeRadioAstronomyObservatory part oftheFCRAOExtragalacticCOSurveyusing14m where DisinunitsofMpc,/(Ha) sumed tobeoftheformA(Ha)=0.08[esc|&|—1],whereb fully sampledCOobservationsofgalaxies(cf.Kenney& be ±30%,basedonacomparisonofmajoraxismapswith the particularCOdistributionassumed. The globalfluxderivedinthiswayisnotverysensitiveto observations whenconvolvedwitha45"Gaussianbeam. eling theradialdependenceofCOemissionineachgal- of theopticalradius.GlobalCOfluxeswerederivedbymod- to theradiusatwhichemissionfellbelowI made alongthemajoraxisofeachgalaxyat45"spacingout where (Youngetal.1995),butabriefdescriptionofthe a half-powerbeamwidthof45".Thedataarepresentedelse- quency oftheCOline(115.271203GHz),telescopehas ergs cms.TheresultingHaluminositiesarelistedin for thegalaxieswehaveimaged inHaarelistedTable3. published intheliterature,indicates thattheglobalCOfluxes with measurementsforthesame galaxiesfromotherstudies measurements fromtheFCRAOExtragalacticCOSurvey CO fluxuncertainties,derivedfromacomparisonofthe Young 1988).Anindependentdeterminationoftheglobal axy, anddeterminingthefluxofmodelwhichbestfit (1) isgivenbyc=10*-^'tThus,theHaluminosityex- conversion factor N(H)//co=2.8X10Hcm [K(T) are accurateto±40%(Young et al.1995).TheCOfluxes = 1K(T*)kms,orifnoemissionwasdetected,outto1/2 co 2 R 2 162 12 Z,(Ha)=4irD/(Ha)C, (1) The meanratioofthefluxwemeasuretoin L(Ha) =3.13X10D/(Ha)C,(2) The HafluxesderivedfromtheCCDimaginghavebeen The uncertaintiesintheglobalCOfluxesareestimatedto Observations oftheCO.7=1—>0emissionweremadeas The Hmasseswerederivedfrom theCOfluxesusing 2 3.2 COFluxesandMolecularGasMasses 3. GALAXYLUMINOSITIESANDMASSES 3.1 HaLuminosities 1911 1996AJ 112.1903Y 1912 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society NGC 278 NGC253 NGC 157 NGC 972 NGC 925 NGC 628 NGC 520 NGC 488 NGC 891 NGC 660 NGC 1087 NGC 1068 NGC 1055 NGC 2336 NGC 2146 NGC 1961 NGC 1614 NGC 1569 NGC 1084 NGC 2683 NGC 2276 NGC 2841 NGC 2798/99 NGC 2775 NGC 2339 NGC 3623 NGC 3593 NGC 3556 NGC 3521 NGC 3504 NGC 3351 NGC 3310 NGC 3184 NGC 3147 NGC 3079 NGC 3077 NGC 3034 NGC 2976 NGC 2903 NGC 3627 NGC 4216 NGC 4212 NGC 4237 NGC 4206 NGC 4194 NGC 4192 NGC 4189 NGC 4157 NGC 4102 NGC 4088 NGC 4178 NGC 4064 NGC 4041 NGC 4038/39 NGC 3810 NGC 3718 NGC 3690/ NGC 3675 NGC 3631 IC 694 Galaxy (1) (Jy km/s) < 960 S(CO) < 880 < 110 < 210 20160 18240 4570 2160 2800 2840 2840 5160 (2) 4660 4920 2740 2280 1260 2070 1120 1360 1870 1360 1130 1040 1440 1330 480 400 500 680 540 920 410 720 800 830 290 610 550 360 800 700 500 620 910 510 940 250 850 660 730 900 140 100 180 60 80 60 90 Table 3.Globalgalaxyfluxes,luminosities,andmasses. (Jy km/s) 1796 < 3.3 S(HI) 425 259 227 402 235 254 128 115 246 170 123 131 118 109 146 173 (3) 63 28 40 47 22 25 24 30 45 29 39 80 95 74 60 86 26 76 28 34 51 84 96 32 43 64 13 10 60 59 11 12 15 43 5.9 63 3.0 6.2 12 3.2 1178 1500 S(60) S(100) 118.3 (Jy) 198.1 48.5 41.5 144.7 26.7 243 17.3 14.0 14.6 (4) (5) 10.7 103 24.6 25.3 72.1 31.0 23.2 33.2 79.4 28.3 53.4 31.6 61.8 20.5 17.6 4.2 66.4 22.2 503 12.3 2.7 73 38.0 51.9 34.8 13.4 3.0 8.5 3.6 0.9 19.2 3.7 15.5 12.9 18.9 19.9 1.1 9.0 2.2 7.4 2.5 3.4 9.8 5.2 8.9 8.4 3.5 Provided bythe NASA Astrophysics Data System 1862 1351 118.8 2503 198.6 104.9 194.8 147.4 102.5 124.8 145.0 49.8 24.5 23.2 71.0 79.6 59.7 32.7 35.2 36.7 28.8 44.5 42.0 46.4 17.6 12.8 49.9 65.6 26.7 24.6 28.6 57.0 62.6 33.3 59.8 30.1 45.8 24.2 28.8 34.0 33.2 26.6 34.1 10.6 28.9 30.4 34.0 39.3 36.7 80.8 10.9 12.4 15.3 9.9 2.4 9.5 7.7 9.8 2.5 11.01 10.80 11.18 10.30 10.27 10.56 10.89 10.63 10.49 10.88 10.80 1134 1034 10.61 1135 10.87 1135 11.04 10.51 10.79 10.65 10.40 10.41 10.91 10.18 10.53 10.38 10.49 10.27 11.28 10.00 10.69 10.61 10.68 1034 10.02 10.01 10.57 10.70 10.24 10.38 10.11 10.46 10.76 1039 1035 10.14 11.15 10.33 10.68 log 9.86 9.30 (6) 9.62 9.12 9.74 9.15 935 9.89 9.77 URol) 7.91 7.19 7.42 < 7.53 7.34 8.48 7.75 7.45 * 8.00 733 8.88* 7.14 8.07 7.90* 8.86 8.62 8.28 8.26 7.46 8.87 8.70 7.78 7.38 7.91 6.65 7.53 7.80 6.33 7.51 * 6.56 831 7.67 7.40 6.84 7.67 7.91 8.04 8.35 8.22 6.72 6.95 738 737 7.06 7.67 7.20 7.42 7.42 7.76 6.99 834 731 7.82 6.64 7.62 8.64 9.00 8.10 8.16 log (7) MOL) <9.34 <8.68 <9.04 <8.64 (Mo) 10.46 10.00 10.08 10.10 10.47 10.15 10.12 10.78 10.26 10.37 10.44 10.29 10.70 10.17 10.28 1038 (8) 9.22 9.40 9.83 9.92 9.78 9.78 7.18 9.90 9.35 7.96 7.92 9.42 9.24 7.09 9.34 9.61 9.81 9.44 9.62 9.60 935 9.35 9.15 8.54 9.73 9.03 9.69 9.45 9.52 9.75 933 9.36 9.07 9.95 8.86 8.42 8.61 933 9.96 M(HI) <8.49 10.40 10.09 10.26 10.10 10.08 10.16 10.31 (Mo) 10.09 10.05 10.22 11.07 10.66 10.22 10.18 9.34 log 10.12 9.77 9.66 9.90 9.95 9.55 8.59 (9) 9.79 9.68 9.83 9.48 9.60 9.01 8.74 8.72 8.82 8.26 8.82 9.42 9.80 9.99 9.98 8.66 8.19 8.51 9.43 9.57 9.59 9.88 9.08 9.82 9.91 8.63 9.95 8.97 8.05 9.87 9.83 9.44 9.77 9.38 9.87 LOR) 10.26 11.12 10.39 10.24 10.43 10.76 10.92 10.64 10.78 10.73 1139 1030 1134 11.72 10.65 10.49 11.08 10.96 10.68 10.96 10.85 1030 10.16 11.04 10.61 10.49 (V 10.35 10.36 10.01 1035 1038 1037 11.11 10.42 10.91 10.06 (10) 11.95 1039 log 9.78 936 9.64 9.72 8.93 9.65 837 8.66 9.72 9.93 9.63 9.75 9.90 9.04 936 9.88 9.62 9.65 9.12 9.93 8.87 M Dust (Mo) 633 6.62 7.30 4.99 737 7.14 723 6.47 729 6.80 6.88 726 7.40 7.17 7.12 7.49 7.13 (ID 7.33 7.45 8.02 4.84 6.70 638 72A 727 6.09 6.71 6.76 5.73 6.51 7.87 6.91 6.77 6.32 6.41 538 6.41 6.45 6.76 6.09 6.80 6.76 6.83 6.65 634 6.93 6.70 6.00 635 6.16 6.91 737 6.64 7.66 6.73 5.82 533 6.96 log 5.78 1912 1996AJ 112.1903Y 1913 YOUNGETAL.\STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System NGC4254 NGC 4299 NGC 4298/ NGC4294 NGC 4293 NGC 4438 NGC 4419 NGC 4413 NGC 4394 NGC 4380 NGC 4351 NGC 4321 NGC 4303 NGC 4498 NGC 4459 NGC 4450 NGC 4424 NGC 4519 NGC 4501 NGC 4522 NGC 4654 NGC 4579 NGC 4571 NGC 4569 NGC 4567/ NGC 4561 NGC 4548 NGC 4536 NGC 4535 NGC 4532 NGC 4527 NGC 4526 NGC 4736 NGC 4689 NGC 4651 NGC 4647 NGC 4639 NGC 4713 NGC 4710 NGC 5194 NGC 5005 NGC 4826 NGC 4808 NGC 6951 NGC 6643 NGC 5248 NGC 7479 NGC 7331 NGC 6946 NGC 6240 NGC 5907 NGC 5631 NGC 7625 NGC 7541 NGC 7217 Mik 231 IC 356 IC 342 Arp 220 NGC 4302 NGC 4568 Galaxy S(CO)S(HI)S(60)S(100)LL(Ha)MO^)M(HI)L(IR)M ßDust (1) (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) (Jykm/s) (Jy)ay)(L^(M^ < 130 < 120 < 100 < 120 < 160 < 60 < 90 < 120 < 120 < 70 < 70 < 35 < 35 < 70 < 30 29220 12370 2560 2170 4160 9450 3000 1570 1800 2280 1550 3340 1500 2220 1190 1260 1280 1050 1440 1230 1200 740 710 730 600 910 200 540 440 420 350 380 270 270 650 300 920 450 210 280 570 100 60 3557 < 8.1 < 3.3 < 2.1 < 1.5 220 244 105 872 177 104 76 39 23 77 42 50 47 73 41 41 25 75 42 21 31 50 30 85 89 12 42 94 35 39 13 11 32 13 12 12 19 16 18 2.0 7 2.5 3.4 7.0 4 7.0 3 7.0 6.6 8.1 3 7.6 302.0 128 161.3 106.6 213 31.6 33.7 21.2 22.1 40.0 73.6 41.6 22.4 25.6 36.5 203 123 37.9 33.3 14.0 10.8 27.310.877.86 20.4 16.4 10.4 14.4 11.5 9.6 6.0 2.6 5.8 63 63 7.0 5.9 5.1 3.0 2.7 13 0.89 0.79 5.7 3.0 5.2 9.1 5.8 1.3 4.0 8.0 0.98 6.8 1.8 1.6 5.0 33 13 1.9 1.8 13 Table 3.(continued) 292 344.4 661.7 135.3 117.8 45.8 663 45.8 49.3 77.4 38.2 21.1 56.6 33.1 43.6 63.9 41.8 20.4 26.9 25.8 32.9 15.9 15.5 12.4 30.8 28.8 13.0 10.1 16.8 16.6 16.4 11.1 10.7 17.7 43 6.4 3.0 5.1 90.2 23.7 69.2 78.6 63.0 11.5 15.8 12.0 4.9 6.0 4.7 2.4 43 3.1 7.1 8.4 5.9 3.4 5.4 10.72 1039 10.09 10.50 10.52 10.51 10.65 10.40 10.29 10.40 10.14 10.03 10.66 10.84 1035 10.63 10.68 10.71 10.78 10.36 10.05 10.49 11.09 11.08 10.77 10.72 10.80 11.04 10.35 10.35 11.45 10.67 10.67 10.97 9.60 9.82 9.45 9.98 9.77 10.26 10.49 10.72 10.85 10.81 10.19 1037 10.55 10.64 10.06 10.37 10.85 Ipg log 9.73 9.95 9.81 9.59 9.49 9.83 9.98 7.76 7.75 7.82 7.87 6.81 7.12 7.03 7.84 7.31 7.61 7.72 7.87 738 7.71 7.26 7.60 7.48 7.43 7.19 7.41 7.78 7.17 7.47 7.68 8.03 7.90 7.94 830 936 8.13 7.39 7.01 8.16 937 7.89* 837 8.14 8.42 < 7.36 739 7.18 7.48 8.21 6.67 6.82 8.01 8.44 739 6.94 7.13 7.47 7.00 7.08 6.71 6.92 7.36 7.96 <8.60 <8.76 <8.72 <8.42 <8.49 <8.49 <8.64 10.22 10.88 <8.19 < 8.199.339.46 10.85 10.88 10.37 10.50 10.35 10.14 <8.72 <8.48 <8.12 <8.85 <8.74 <8.72 9.51 9.84 9.90 9.51 9.42 9.60 9.22 9.82 9.83 9.38 9.09 9.49 9.19 9.80 9.98 9.80 9.13 8.94 9.75 9.52 9.81 9.62 9.46 9.74 10.12 9.8610.60 10.17 10.00 9.75 93610.01 9.07 <8.889.72 9.61 9.09 9.30 8.97 9.99 8.39 < 10.35 <8.30 <8.49 10.00 10.03 1032 10.32 10.04 10.10 1031 1033 10.51 10.00 9.60 9.47 9.31 9.37 9.08 9.85 9.84 9.05 8.82 9.65 9.67 9.10 8.82 10.086.67 9.72 9.32 9.91 9.59 8.79 8.88 935 9.58 8.74 8.96 8.82 9.06 9.39 9.94 9.67 10.49 9.85 10.57 9.78 837 9.13 831 9.02 9.02 838 8.84 9.59 9.45 9.05 8.44 8.39 8.62 10.40 10.41 10.16 1030 10.51 1033 10.64 10.08 10.43 10.49 10.12 10.71 10.61 12.00 10.94 10.79 12.61 10.19 12.40 10.47 1131 10.11 10.44 9.92 9.84 937 9.13 9.74 9.86 9.35 9.96 9.87 9.86 9.71 9.79 9.64 9.87 9.44 9.72 9.88 9.18 9.32 9.74 9.47 936 9.38 9.57 9.55 6.46 7.03 6.75 6.52 6.80 6.15 6.89 5.91 6.86 6.77 637 5.65 6.19 633 6.43 631 6.53 6.01 6.93 7.17 6.96 7.18 6.40 6.17 631 7.31 7.92 7.05 6.99 6.09 7.11 7.00 5.71 5.84 7.44 6.93 733 7.06 6.85 7.64 735 6.27 6.33 5.94 5.73 7.04 6.66 637 832 832 6,01 6.03 6.58 5.86 7.17 5.79 5.85 1913 >H o00 CM^ 1914 YOUNG ETAL.: STAR FORMATION IN SPIRAL GALAXIES 1914 \—I Notes to Table 3 ; Col. (1) Galaxy name—NGC, IC, Mrk, or Arp designation. ^ Col. (2) Global CO flux, in units of Jy km/sec, from the FCRAO Extragalactic CO Survey (Young et ai 1995). The CO flux is that of the model distribution á which best matches the observed distribution of CO integrated intensities when sampled with a 45" Gaussian beam. The models are truncated at the radius of S the outer edge of the telescope beam for the outermost CO observation. Corrections for source-beam coupling are applied. Uncertainties arising from ^ incomplete sampling of the disk are typically ~20%. The overall la uncertainty in the global CO flux is —30%. Upper limits are 2a. Col. (3) Global HI flux, in units of Jy km/sec, from the compilation of Huchtmeier et al. (1983). Upper limits are 2o\ Col. (4) IRAS flux density at 60 jam. For the galaxies smaller than 8’, the flux densities listed are those derived from one-dimensional coaddition of the IRAS data, or Addscans, using the post-November 1988 calibration. (The November 1988 calibration corrected for a systematic error between the point source and Addscan flux densities, thereby placing the Addscan flux densities on the Point Source Catalogue scale.) For the galaxies larger than 8’, the flux densities listed are based on the IRAS Survey two-dimensional coadded flux densities of Rice et al. (1988). An additional calibration factor of 1.18 has been applied to the 60 fim data of Rice et al., since the one-dimensional Addscan flux densities are 1.18 times higher than the two-dimensional Survey coadded flux densities for galaxies between 5’ and 8’ in size (see Devereux and Young 1990, Appendix). The la uncertainty in the flux densities is ~10%. Col. (5) IRAS flux density at 100 fim. For the galaxies smaller than 8’, the flux densities listed are those derived from one-dimensional coaddition of the IRAS data, or Addscans, using the post-November 1988 calibration. For the galaxies larger than 8’, the flux densities listed are based on the IRAS Survey two-dimensional coadded flux densities of Rice et al. (1988), with no additional calibration factor since the one- and two-dimensional coadded flux densities agree at 100 fim for galaxies between 5’ and 8’ in size (see Devereux and Young 1990, Appendix). To lor uncertainty in the flux densities is —10%. Col. (6) Logarithm of the blue luminosity in units of L0, derived from the blue magnitude corrected for Galactic and internal absorption, as listed in Table I, and assuming MB(Sun)=+5.48. Col. (7) Logarithm of the Hor luminosity in units of L0, corrected for foreground Galactic extinction. The luminosity is derived from the distance D and the extinction-corrected Ha flux [f(Hor)], where L(Ha)=47rD2 f(Ha). The Galactic extinction correction in magnitudes is of the form A(mag)=0.08(csc|b|-1), where b is the Galactic latitude of each galaxy. The values listed include no corrections for extinction internal to the galaxies in question. Galaxies indicated by an asterisk are those for which internal extinction corrections have been determined from [Sill] imaging (Young, Kleinmann, and Allen 1988). The corrected Hor luminosities for these galaxies, in the same units as the values in column 7 of this Table, are: NGC 520 (8.83), NGC 660 (9.32), NGC 1068 (9.12), NGC 2146 (8.72), NGC 3034 (8.12), and Arp 220 (9.68). Col. (8) Logarithm of the global molecular gas mass in units of Mq, computed from the global CO flux [S(CO)] from Col. (2), and assuming a CO—^H 20 2 2 conversion constant of N(H2)/I(CO)=2.8X10 H2/cm /[K(TR) km/sec] (Bloemen et al. 1986). For this value of the conversion factor, the H2 masses are given by M(H )=1.1X104 D2 S(CO), where D is the distance in Mpc. Upper limits are la. 2 5 Col. (9) Logarithm of the atomic gas mass in units of M0, computed from the global HI flux in Col. (3). The HI mass is given by M(HI)2.36X10 D2 S(HI), where S(HI) is the HI flux in Jy km/sec, and D is the distance in Mpc. Upper limits are 2cr. Col. (10) Logarithm of the far-infrared luminosity from ~1 to 500 /¿m in units of L0, computed from the IRAS 60 and 100 fim flux densities. The IR luminosity is given by L(IR)=3.75X105 D2 C [2.58 S(60)+S(100)], where D is the distance in Mpc, S(60) and S(100) are the IRAS flux densities listed in Columns (4) and (5) in Jy. The constant C corrects for the flux missed shortward of 40 /¿m and longward of 120 /mi, and is a function of the S(60)/S(100) ratio; the values of C are given in Table B.l of Catalogued Galaxies in the IRAS Survey (1985). The la uncertainty in the luminosities is —10%. Col. (11) Logarithm of the warm dust mass in units of M0, computed from the 100 /mi flux density, the dust temperature (Tdust) implied by the ratio of 60 to 100 /mi flux densities, and the grain properties (size, density, and emissivity) given by Hildebrand (1983). The mass of warm dust emitting at 100 /mi is 2 given by Mdust=4.78 S(100) D [exp(143.88/Tdust)—1], where Tdust is in °K and D is in Mpc.
km s-1]-1 (Bloemen et al 1986). Kenney & Young (1989) where D is the distance in Mpc and ^(CO) is the CO flux in 1 show that this value of the conversion factor leads to H2 Jy km s“ . masses in solar units given by There has been much discussion in the literature of the 4 2 accuracy of molecular gas masses for galaxies. Of interest M(H2) = 1.1X10 D S(CO), (3) here are the global H2 masses in luminous spiral galaxies. g -10
tj>-> 3 -10.5 —
-11 — t % -11.5 ö ft X A SO, Sa, Sab, Sb pXH ■ Sbc, Sc Ù0 -12 o Scd, Sd, Sdm, Irr # Pairs & Mergers ..1 I _i J— I I -12.5 -12 -11.5 -11 -10.5 log F(Ha) erg s 1 cm 2 (KK and K87) Fig. 3. Galaxy inclinations, plotted as a function of morphological type, for the 120 galaxies in the Ha imaging survey. Solid symbols indicate the Fig. 4. Comparison of Ha fluxes for 45 galaxies in the present study which galaxies classified as peculiar. The inclinations, listed in Table 4, were de- overlap with the galaxies studied by Kennicutt & Kent (1983) and Kennicutt rived following Roberts (1969)—also see note to column 4 in Table 4. et al. (1987). Galaxies are coded by morphological type as indicated.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1903Y -1 With regardtotheabsoluteaccuracyofMilkyWay in M31(Vogeletal1987)andM33(Wilson&Scoville that themolecularcloudswhichhavebeenspatiallyresolved galaxies, Young&Scoville(1991;cf.Fig.1)haveshown M33. lecular cloudsintheSbgalaxyM31andScd conversion factorfortheMilkyWayalsoappliestomo- clouds intheinnerandouterMilkyWay(Scovilleetal. CO—>H conversionfactorwhenappliedtoluminousspiral The globalmoleculargasmassesforthegalaxiesinthis considerably moreuncertain(cf.Maloney&Black1988). gas massesforthelowmetallicityirregulargalaxiesmaybe global Hmassesforluminousspiralgalaxies.Themolecular vided thatthemeasurementreferstoglobalHIfluxof from thecompilationofHuchtmeieretal.(1983,1988),pro- the galaxy.ThespecificreferencesforHImeasurements sample arelistedinTable3. 1915 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES IRAS fluxdensitiesat60and100jamusingthepost- listed inTable3.Theuncertaintiesthesevaluesareof Jy kms.TheglobalHIfluxesandatomicgasmassesare where DisthedistanceinMpcandS(Hl)HIflux of atomichydrogeninsolarmassesisgivenby are listedelsewhere(Youngetal,inpreparation).Themass uncertainties inthemoleculargasmasses. November 1988calibration.Forgalaxiessmallerthan8'in order 30%(cf.Huchtmeieretal1983,1988),similartothe 1990) havesimilarratiosofCOluminositytovirialmassas 1987; Solomonetal.1987).ThisimpliesthattheCO—»H diameter, wehaveusedtheone-dimensionalcoaddedIRAS tween 5'and8'indiameter(seeYoungetal1989;De- Addscan fluxdensitiesare1.18timeshigherthanthetwo- plied tothe60jamdataofRiceetal,sinceone-dimensional coadded IRASSurveyfluxdensitiesreportedbyRiceetal data, oraddscanstodeterminethefluxdensities.Forgalaxies vereux &Young1990b,Appendix).TheIRAS60and100 dimensional Surveycoaddedfluxdensitiesforgalaxiesbe- 8' indiameterandlarger,wehavéusedthetwo-dimensional given inTable3. jam fluxdensitiesforthegalaxiesinpresentsampleare (1988). Anadditionalcalibrationfactorof1.18hasbeenap- data. Thefar-IRluminosityis givenbyLonsdaleetal 2 derived usingthefluxdensities determinedfromtheIRAS 2 (1985) as 2 3.4 IRASFluxDensities,Far-IRLuminosities,andWarm 52 2 _14 In thispaper,weadopt±30%astheuncertaintyin M(H I)=2.36X10DS(Hl),(4) HI fluxesforthegalaxiesinoursamplehavebeentaken The infraredluminositiesusedherearebasedoncoadded L(IR) =47tD[1.26C{2.58X10 5(60)+1.0 The far-IRluminositiesfrom~1to500jamhavebeen © American Astronomical Society • Provided by theNASA Astrophysics Data System 3.3 HlFluxesandAtomicGasMasses _14 X 105(100)}], (5) Dust Masses -2 between the60and100/¿mbandpassesfilterre- where Disthedistance,factor1.26correctsforgap longward of120/¿mandshortward40/mi.Thevalues from TableB.lofCataloguedGalaxiesintheIRASSurvey ponent, themassofwarmdustisgivenby Hildebrand (1983)andassumingasingletemperaturecom- mass ofwarmdustineachgalaxy.Followingtheanalysis Table 3.Thefar-IRluminositiesarepresentedin where DisinMpc,5(60)and5(100)areJyaslisted sponse, andtheconstantCisacorrectionfactorforflux temperature 7at100jam.Usingthegrainsize,density,and where aistheweightedgrainsize,pdensity, (1985). Insolarunits,Eq.(5)becomes C areafunctionofthe5(60)/Si100)ratio;theytaken g cm.Themassof100jamemittingdustthenbecomes emissivity givenbyHildebrand(1983),(4/3)flpgo=0.04 peratures ^20Kemittingpredominantlyatwavelengthsbe- where thedustmassisinsolarmasses,5(100)Jy,D at 100jam,and/?(100,7)istheintensityofblackbody Table 3. yond 100jam.Thus,thedustmasswederivewillbereferred with temperatures^25Kbutnottocolderdusttem- vereux &Young(1990b),IRASissensitivetowarmdust in K.AsdiscussedYoungetal.(1986b,1989)andDe- the distanceinMpc,andTiswarmdusttemperature g loois100jamgrainemissivity,Sthefluxdensity to asthe“warmdustmass.”Thesemassesarelistedin Ha luminositiesofgalaxiesagivensurfacearea,although the face-onopticalareas.Thereisconsiderablescatterin Ha luminositiesforthegalaxiesinoursampleplottedversus tical area,intheabsenceofextinction.Figure5(a)shows face area,theHaluminositieswouldscalelinearlywithop- ders ofmagnitude,asdotheopticalareasgalaxies.If triangles representthe22galaxieswhosetypeclassifications in generalthelargergalaxiesaremoreluminous.Thesolid all galaxiesproducedthesameHaluminosityperunitsur- line representsthemeanHasurfacebrightnessforallof include thedesignationofpeculiar(seeTable1).Thedashed in Fig.5(b),thistimewiththe highly inclinedgalaxiesindi- found amongthemorenormalgalaxies. liar galaxiesexhibitthefullrangeofHasurfacebrightness galaxies inthesample.ThedataFig.5indicatethatpecu- The differenceinthesetwo fits indicatesthatthemore with inclinationslessthan70°, whilethedottedlinerepre- cated. Inthisfigure,thedashed lineisafittothegalaxies face-on galaxies haveHasurfacebrightnesses ~3times sents afittothegalaxieswith inclinations greaterthan70°. 10 dust m 52 2 21 We havealsousedtheIRASfluxdensitiestoestimate L(IR) =3.75X10DC[2.585(60)+5(100)],(6) ^Dut=(4/3)apßioo[5iooD/ß(100,r)], (7) ^=4.785(100)D[ep(143.88/r)-], (8) The Haluminositieswederivespanmorethanthreeor- 4.1 GlobalHaLuminositiesandSurfaceBrightnesses The Haluminositiesversusopticalareasarealsoshown S DustXdust 4. STARFORMATIONINGALAXIES 1915 1996AJ 112.1903Y Fig. 5.Haluminositiesforthegalaxiesinimagingsurvey,plotted related torealvariationsintheHasurfacebrightnesses est Hasurfacebrightnessrepresentstheedge-ongalaxyM82. face brightnesswhichisafactorof3timeshigherthanthatthehighly the lessinclinedgalaxies.Themoreface-ongalaxieshaveameanHasur- axies, whilethedashedlinerepresentsmeanHasurfacebrightnessof line representsthemeanHasurfacebrightnessofhighlyinclinedgal- 70°, whileopensymbolsrepresentthemoreface-ongalaxies.Thedotted where thesolidsymbolsrepresentgalaxieswithinclinationsgreaterthan Ha surfacebrightnessforallofthegalaxiesinsample,(b)Sameas(a), are classifiedaspeculiar(seeTable1).Thedashedlinerepresentsthemean given inTable1(fromRC2).Thesolidsymbolsrepresentgalaxieswhich versus theface-onareaofgalaxy.GalaxyareaswerederivedfromD unit face-onsurfacearea,orthe Hasurfacebrightness,asa fore, someofthescatterinFig.5isrelatedtoextinction, greater inthemeanthanhighlyinclinedgalaxies.There- inclined galaxies.Thehighlygalaxy(filledtriangle)withthehigh- function ofthegalaxyinclination. Althoughthereisalarge the Haluminosity,weshowin Fig. 6theHaluminosityper among galaxies. each inclination, thereisatrendofdecreasing Hasurface above whichtheextinctioncauses asignificantreductionin some isrelatedtomeasurementuncertainties,and scatter intheobservedHasurface brightnessesofgalaxiesat 1916 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES 25 In ordertodeterminetheapproximategalaxyinclination © American Astronomical Society • Provided by theNASA Astrophysics Data System Fig. 6.Hasurfacebrightnessesplottedasafunctionofthegalaxyinclina- pronounced effectforgalaxieswithinclinationsgreaterthan trend ofdecreasingHasurfacebrightnesswithincreasinginclination. tion. Theinclinations,listedinTable4,werederivedfollowingRoberts in theHasurfacebrightnessesofpeculiargalaxieswhen tions greaterthan70°arereferredtoasthe“highlyin- brightness forthehighlyinclinedgalaxies,withmost resent theremaininggalaxiesinsample.Althoughthere Fig. 7(b)displaysthedatafor96galaxieswithi<70°; luminosities versusface-onopticalareasasinFig.7(a), these galaxies;thegalaxiesclassifiedaspeculiarareindi- the figurerepresentsfittoHasurfacebrightnessesof Ha luminositiesversustheface-onopticalareasof96 clude thehighlyinclinedgalaxies.InFig.7(a),weshow clined” galaxies. 70°. Inthediscussionwhichfollows,galaxieswithinclina- Deharveng etal (1994),andbothstudiesagree thattheSd-Ir teracting systems. the mean,Haluminosityperunitface-onsurfaceareais tems havehigherthanaverageHasurfacebrightnesses.In galaxies tendtohavelowerthanaverageHasurfacebright- nesses withineachtype,itisclearthattheearly-typespiral is considerablescatterintheobservedHasurfacebright- the dottedlinerepresentsfitforall96galaxies,large where thedataarenowcodedbygalaxytype.Eachpanelof of theHasurfacebrightnesses,inFig.7(b)weshow compared withthemorenormalgalaxiesinsample. cated withfilledsymbols.Wefindnosignificantdifference (1969). Galaxiesarecodedbymorphologicaltypeasindicated.Notethe Hubble sequencewiththeUVsurface brightnessesfoundby axies inoursamplerelativeto the later-typespiralsandin- a factorof2.6timesloweramong theearly-typespiralgal- nesses, whilethelatest-typespiralsandinteractingsys- symbols representthetypeindicated,andsmalldotsrep- systems withinclinationslessthan70°.Thedashedlinein surface brightnessesamonggalaxies,itisnecessarytoex- CM [Xh o -3 3 Pi O Ofl CÖ O a 03 I In ordertoinvestigatethemorphologicaltypedependence In ordertoinvestigatetheintrinsicvariationsinHa We havecomparedtheHasurface brightnessesalongthe Inclination (Degrees) 1916 1996AJ 112.1903Y 2 higher thanforSa-Sbgalaxies,respectively.Thesemeanval- there isasmalldifferenceinthemeanHasurfacebrightness we excludethepeculiargalaxiesinoursample,differ- ues aresampledependent,asDeharvengetal.noted;when times higherthanforSbc-Scdgalaxies,andabout3 galaxies haveHaandUVsurfacebrightnessesabout1.3-1.4 1917 YOUNGETAL:STARFORMATIONINSPIRALGALAXIES morphology issignificantataboutthe3-4
40 \ ^ O -5 -4 -3 -2 log [L(Ha)/L(IR)l Fig. 9. Histogram of the ratio of Ha to far-infrared luminosity for all of the galaxies in this study (grey area), and for the galaxies with inclinations greater than 70° (black area). Also included in the solid histogram are four peculiar galaxies which suffer severe extinction near the nuclei—NGC 520, 660, 2146, and Arp 220. The luminosity ratios expected for high mass stars are indicated by the dashed lines near the top. Figures 10(a) and 10(b) show the ratio L(Ha)/L(IR) as a function of morphological type for the entire sample. It is clear that there is little difference among spiral galaxies of types Sab-Scd in the observed ratio of Ha to far-IR luminos- ity. The morphological categories which seem to be charac- terized by slightly elevated values of L(Ha)/L(IR) include types Sd-Im; conversely, the categories with slightly lower values of L(Ha)/L(IR) include types SO-Sa. There are several reasons why one might observe a dif- ference in the L(Ha)/L(IR) ratio between SO-Sa galaxies and Sd-Ir galaxies. Some of this tendency could be due to increased Ha absorption in the early-type galaxies by the underlying stellar population. Additional effects may be the result of metallicity variations along the Hubble sequence. As described by Devereux & Young (1990a), the ratio L(Ha)/L(IR) is extremely sensitive to the mass of the highest mass stars which form, since the Ha to far-IR luminosity ratio spans more than a factor of 1000 for 05 through B5 stars. Therefore, it is reasonable to expect that the L(Ha)/ L(IR) ratio will also be sensitive to metallicity, since higher mass stars may form in regions of lower metallicity, accord- ing to the Jean’s criterion. It is well known that Sd, Sdm, and Im galaxies are metal poor (cf. Pagel & Edmunds 1981), so that stars of higher mass are likely to be forming in these systems. Another possibility is that the stars which form in the low metallicity systems have higher effective tempera- tures without an increase in the effective mass (cf. Garcia- Vargas 1995). Lastly, in regions of lower metallicity there is less dust present to absorb the bolometric luminosity, and this could lead to lower far-IR luminosities per unit Ha lu- Fig. 10. (a) The ratio of Ha to far-inffared luminosity plotted as a function minosity. Any of these possibilities could account for the of morphological type. The galaxies with inclinations greater than 70° are slightly higher L(Ha)/L(IR) ratio observed in the Sd-Irr gal- plotted as filled symbols. The ratios expected for high mass stars are indi- axies relative to the SO-Sa galaxies indicated in Fig. 10. cated. Note that galaxies of types Sa through Scd exhibit similar ranges of observed values for the Ha to far-IR luminosity ratio, (b) Histograms of the Figure 10 also indicates that the L(Ha)/L(IR) ratio in the ratio of Ha to far-infrared luminosity as a function of morphological type. pairs and mergers is slightly lower than for the spirals. There The hatched histograms represent galaxies with inclinations <70°, while the are several possible explanations for this effect. First, the Ha open histograms below represent the highly inclined and obscured galaxies. © American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1903Y be unusuallyhighgasconcentrations(andextinction)inthe luminosity maybereducedbecauseofextinctionandgeom- the nucleus. luminosities duetothepresenceofanonthermalsourcein be contributingtothelowerL(Ha:)/L(IR)ratiosinpairs inner regionsofthesegalaxies.Anothertrendwhichcould mine ameaningfulinclination,andpartlybecausetheremay etry. Eventhoughthehighlyinclinedgalaxiesareindicated the globalstarformationefficiencymeasuredintwodiffer- yield ofyounghighmassstarsperunitgasavailable and mergersisthatthesegalaxiesmayhaveenhancedIR axies haveunusualmorphologiesanditisdifficulttodeter- systems withsmallerinclinations,partlybecausethesegal- separately, therecouldbeconsiderableextinctionevenin lar gas.Weexaminethetrendsinglobalstarformation yield ofyoungstars,andsecond,usingthefar-infrared ent ways—first,usingtheHalineluminositytotrace to formthosestars.Inthefollowinganalysis,weinvestigate L(Ha)/L#(H), L(IR)L#(Hand5(60)/5(100).Weremind nosity isanequallygoodtracerofthehighmassstarforma- the abovemeasuresofSEE.Oneconsequence efficiency asafunctionofmorphologyalongtheHubble luminosity—both normalizedbytheglobalmassofmolecu- L(Ha)/^(H) vsL(IR)/^#(Hispresentedwiththegalax- from majoraxisCOobservations(seeSec.3.2),whilethe the readerthatglobalmoleculargasmasseswerederived tion, andenvironment,aswelltheglobalratios information inthistableincludesthegalaxytype,inclina- the galaxiesinthisstudysortedbymorphologicaltype.The tion rateastheHaluminosity. comparisons weshowistheillustrationthatFIRlumi- between thesetwoquantitiesforallmorphologies,inthat sequence andasafunctionofgalaxyenvironmentforboth 1920 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES high massstarformation,thecorrelationofL(Ha)/^M(H) in spiralgalaxiesisfromHnregionsandassociatedwith elevated valuesofL(Ha)/^#(H).SincetheHaluminosity ies codedbymorphologicaltype.Thereisaclearcorrelation of theglobalstarformationefficiency.Thisplot within andamongthesegalaxies. comparison ofHaandCOfluxesinthesame45"apertures flux oftheentiregalaxy.Inalaterpaper,wewillpresent global HaandIRluminositiesarederivedbyintegratingthe illustrates that,forthegalaxies in oursample,themeanrate ratio asafunctionofmorphological typeforthe96galaxies IR luminosityalsotraceshighmassstarformation. with L(IR)/^(H)stronglysupportsthesuggestionthat galaxies withelevatedvaluesofL(Ha)/^S(H)alsohave in oursamplewithinclinations lessthan70°.Thisfigure of highmassstar formationperunitmassofmolecular gas 2 2 2 2 2 2 5. THEGLOBALSTARFORMATIONEFFICIENCYINGALAXIES The starformationefficiency(SEE)isameasureofthe Table 4presentstheglobalstarformationefficienciesfor Figure 11showsacomparisonoftwodifferentmeasures Figure 12showshistogramsof theglobalL(Ha)/^#(H) 2 © American Astronomical Society • Provided by theNASA Astrophysics Data System 5.2 DependenceoftheSFEon Morphological Type 5.1 DefinitionoftheStarFormationEfficiency through Sc.Forcomparison,wealsoshowthedistributions We concludethatHubbletypeplayslittlerole,ifany,in phological type.Thesedistributionsalsoindicateasimilar lecular gasfromtypetoforSOthroughScdgalaxies. mean valueofthestarformationrateperunitmassmo- of L/^(H)forthesamegalaxiesasafunctionmor- L(Ha)/L(IR) iselevatedintheirregulargalaxies[cf.Sec.4.3 ratios ofbothL(Ho;)/^#(H)andHowever,in- been underestimated,leadingtoanoverestimateofthemean logical categories.Thesegalaxiestendtobecharacterizedby the irregulargalaxies,meanratiosofbothL(Hor)/^(H) galaxies inoursample. of moleculargasinthesegalaxies. determining themeanyieldofhighmassstarsperunit shows littlevariationwithmorphologicaltypefortypesSa low luminosities,smallsizes,andmetallicities.Itispos- L(Ha)/^#(H) relativetoL!^Mi}3),especiallysincethe comparison oftheHaluminosities,IRandmo- dependent oftheHmassestimates,wenotethatratio and L/^(H)arehigherthanforanyoftheothermorpho- NGC 1055withi=69°)cansuffersevereextinction.Thus, the ratioarefoundforL(Ha)/^#(H)withineachmorpho- the Lj^S{H)distributionsisthatmoreextremevaluesin majority ofthespiralgalaxies. above andFigs.10(a)10(b)].Thus,theresultsof sible thatthemoleculargasmassesforthesegalaxieshave portant roleintheevolutionofgalaxies(Arp1966;Toomre uncertainties, andsomereflectsrealdifferencesinthestar more inclinedgalaxiesinthesample(i.e.,Sbgalaxy logical typethanforExtinctionwithinthesegal- lecular gasmassesindicatesthatthelatetypespirals(Sd-Sm) the effectsofgalaxy-galaxyinteractionsonratestar formation efficiencyfromgalaxytogalaxy. extinction, someofthescatterisaresultmeasurement axies willcertainlyintroducesomeadditionaldispersionin and theirregularsdiffer,infact,whencomparedwith members is<3',sobothgalaxies appearinthesameCCD included (pairsinwhichthe angular separationbetween peculiarities (Schweizeretal.1983; Joseph&Wright1985; based onthepresenceoftidal tails orothermorphological isolated galaxies.Ninesystemsareclassifiedasmergers, close pairs,Virgospirals,groupmembers,fieldand includes galaxiesinawiderangeofenvironments:mergers, tion areelevatedininteractingsystems. that boththeratesandefficienciesofhighmassstarforma- et al.1986;Solomon&Sage1988;Tinney1990)show efficiency ingalaxies(Youngetal.1986a,1968b;Sanders formation (Bushouse1987;Kennicuttetal.1987)andits & Toomre1972;LarsonTinsley1978).Recentstudiesof some oftheobservedscatterinL(Ha)/^M(H)isaresult field). Thetenisolated spiralgalaxiesinourstudy werecho- Sanders etal.1987),andanadditional sixclosepairsare ir2 2 2 2m 2 ir2 2 w2 2 Table 5summarizesthemeanvaluesofSFEfor Among thelatesttypespiralgalaxies(Sd-Sm)andamong The sampleofgalaxieswhichwehaveimagedinHa Galaxy environmenthaslongbeenknowntoplayanim- One notabledifferencebetweentheL(Hof)/^#(H)and 2 5.3 EffectsofEnvironment 1920 1996AJ 112.1903Y 1921 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System Moiphology GalaxyType SO &SO/a Sa Sab Sb Sbc (1) (2)(3) NGC 4293 NGC 3593 NGC 4710 NGC 4526 NGC 4459SA(s)0+ NGC 4438SA(s)0/apec NGC 3718 NGC 3623 NGC 4424 NGC 4419 NGC 4064 NGC 7625 NGC 4192 NGC 3504 NGC 2775 NGC 4826 NGC 4569 NGC 4450 NGC 4351 NGC 4736 NGC 7217 NGC 1055 NGC 2683 NGC 1068 NGC 4102 NGC 3675 NGC 3627 NGC 3351 NGC 2841 NGC 4413 NGC 4394 NGC 4380 NGC 4216 NGC 4157 NGC 4501 NGC 4579 NGC 4548 NGC 488 NGC 278 NGC 891 NGC 2339 NGC 2336 NGC 3147 NGC 2903 NGC 4088 NGC 4041 NGC 3521 NGC 4212 NGC 4206 NGC 4303 NGC 4237 NGC 4527 NGC 4321 NGC 157 NGC 4536 NGC 4639 Table 4.Globalgalaxypropertiesasafunctionofmorphologicaltype. IC 356 (R)SAB(s)ab 36 SB(rs)ab pec46 (R)SB(s)0/a SA(s)ab pec (R)SA(rs)ab SA(rs)a pec SA(r)0+ sp SAB(s)b sp (R)SA(r)ab SB(s)a pec SB(s)a pec (R)SA(r)ab (R)SA(rs)b SAB(rs)ab (R)SB(rs)b SB(s)a sp SAB(rs)bc SA(s)b sp SAB(s)ab 74 SAB(rs)bc SAB(rs)bc SAB(rs)bc SAB(rs)bc SAB(rs)bc SAB(rs)bc (R)SB(r)b SAB(rs)a SAB(S)0 SAB(rs)bc SAB(rs)bc SA(sXVa SAB(rs)b SAB(r)bc SAB(rs)b SAB(s)bc SAB(s)bc SAB(s)b SAB(s)b SAB(s)b SA(s)ab 45 SA(r)ab 45 SA(rs)bc SA(rs)bc SA(rs)b SA(rs)b SB(rs)b SA(rs)b SA(s)bc SBb sp SB(s)a SA(r)b SA(s)b SA(r)b SB(r)b SAbc Inc. Env.LCHoO/MfltyLORl/MO^) (4) (5)(6)(7) (°) (VNy(L^ 43 76 67 79 75 68 71 67 67 61 22 61 63 40 40 40 57 35 48 69 32 64 86 60 80 49 59 25 80 82 54 49 55 12 40 58 28 60 56 37 37 47 60 47 67 25 45 72 83 67 28 18 Isolated Isolated Isolated Isolated Isolated Isolated Group Virgo >-2.14 Virgo -1.50 Virgo -1.90 Virgo -1.24 Virgo >-0.73 Virgo Virgo Virgo Group Virgo Virgo Field -2.23 Virgo Virgo Field Field Field Virgo Virgo Virgo Field Field Virgo Field Field Virgo Virgo Virgo Field Field Field Field Field Field Field Field Field Field Virgo Virgo Virgo Virgo Virgo Virgo Field Virgo Virgo Field Field Field >-2.40 > -1.92 > -1.81 >-1.90 > -1.18 > -1.63 > -1.18 -2.32 -1.62 -1.72 -139 -1.56 -1.89 -1.95 -1.96 -2.38 -132 -2.35 -1.78 -1.96 -1.59* -3.01 -2.81 -2.56 -1.31 -232 -1.31 -1.96 -1.47 -1.86 -237 -2.03 -1.91 -1.96 log -2.35 -1.35 -1.99 -2.03 -1.39 -2.04 -2.47 -1.64 -1.98 -1.77 -1.65 -1.59 -1.98 -2.16 -1.56 -2.08 -1.75 > 1.24 >0.53 >0.08 >0.23 >0.54 >0.41 > 1.06 >035 >0.86 0.65 0.65 0.77 0.84 0.27 0.95 0.29 0.85 0.39 0.27 037 0.66 0.59 0.77 0.37 039 1.08 0.97 0.83 0.35 0.64 0.40 0.78 0.11 1.01 0.52 0.31 0.56 0.45 033 0.23 0.93 0.36 0.36 1.03 0.74 0.68 0.34 0.67 0.41 1.13 0.55 0.74 0.57 0.60 0.32 0.90 1.09 S(60) 0.42 0.45 0.52 0.47 0.38 0.36 0.36 0.23 0.50 0.48 0.51 0.55 0.23 0.21 0.33 0.37 0.65 0.40 0.54 0.29 0.52 0.24 031 0.57 0.21 039 0.79 0.37 0.36 0.46 0.51 0.35 0.68 0.29 0.32 0.35 0.21 0.29 0.21 0.29 0.21 0.42 0.42 0.58 0.27 0.42 0.28 0.45 0.45 0.45 0.41 0.48 0.30 0.36 0.69 0.51 0.37 1921 1996AJ 112.1903Y 1922 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES © American Astronomical Society • Provided by theNASA Astrophysics Data System continued Moiphology Sb Sc 10 Scd Sdm &Sm Sd Isolated Galaxies (1) NGC 5907 NGC 4651 NGC 4647 NGC 4535 NGC 1961 NGC 6951 NGC 6946 NGC 3556 NGC 3521 NGC 3147 NGC 2903 NGC 2775 NGC 6946 NGC 4808 NGC 4654 NGC 4498 NGC 4294 NGC 4189 NGC 3556 NGC 3184 NGC 7479 NGC 6643 NGC 4254 NGC 3810 NGC 3631 NGC 3079 NGC 2976 NGC 2276 NGC 1087 NGC 7541 NGC 7331 NGC6951 NGC5248 NGC5005 NGC4689 NGC 4519 NGC 4522 NGC 1084 NGC 4561 NGC 4299 NGC 4178 NGC 4713 NGC 4571 NGC 3034 NGC 4532 NGC 1569 NGC 3077 NGC 628 NGC 253 NGC 157 NGC 925 NGC 972 Galaxy IC 342 (2) SB(rs)bc pec SAB(rs)bc SAB(rs)bc SAB(rs)bc SB(s)cd sp SB(s)cd sp SAB(rs)cd SAB(rs)cd SAB(rs)cd SAB(s)dm 22 SAB(rs)cd SAB(rs)cd SB(s)c sp SB(s)cd sp SA(s)c sp SAB(rs)c SAB(rs)c SAB(rs)c SAB(s)cd SAB(rs)bc SAB(rs)cd SAB(rs)bc SAB(rs)bc SAB(rs)bc SB(rs)dm 34 SB(rs)din 69 SA(rs)bc SAB(rs)d 49 SAB(rs)c SAc pec SAB(s)c SA(s)bc SAB(s)d 53 SAB(s)c SA(rs)c SA(rs)bc SA(s)cd SB(s)cd SA(rs)c SA(rs)c SB(rs)d 45 SA(s)c SA(s)c SA(s)c SA(s)c SA(r)ab SA(r)d 38 SB(s)c 10 pec Type 10 sp IBm IBm (3) 10 Table 4.(continued) Inc. (4) 45 46 49 42 (°) 70 71 62 28 77 61 22 78 30 43 28 59 30 46 36 67 77 89 67 76 38 59 25 30 30 61 52 56 18 67 45 38 80 59 49 77 60 28 60 12 30 30 Isolated Isolated Isolated Isolated Isolated Isolated Isolated Isolated Isolated Isolated Isolated Isolated Virgo Group Group Virgo Virgo Virgo Virgo Virgo Virgo Virgo Virgo Virgo Virgo Virgo Field Field Field Field Field Field Virgo Virgo Virgo Field Field Field Field Field Field Field Field Virgo Virgo Virgo Field Field Env. LOicO/MOy Field Field Field Field Field (5) (6) > -1.95 >-1.64 >-0.80 >-0.71 >-0.91 > -1.38 > -1.17 > -1.59 >-1.60 >-0.67 (W +0.15 -1.99 -2.00 -2.12 -1.55 -2.11 -1.71 -1.84 -1.68 -1.71 -0.91 -2.03 -2.80 -1.98 -1.91 -0.76 -1.83 ’ -1.86 -1.98 -2.28 -1.68 -2.04 -2.47 -1.89 -1.35 -1.64 log -2.28 -1.77 -2.02 -1.91 -1.71 -1.80 -2.36 -1.36 -1.67 -1.92 -1.50 -1.64 -1.78 -2.06 -1.95 -2.21 -2.24 LORyMOty (VMo) > 133 >031 >0.54 > 121 >0.82 >0.44 > 1.20 >1.22 > 1.49 >0.41 log (7) 0.83 0.49 0.44 0.48 0.63 0.48 0.53 0.68 0.59 0.46 0.87 0.84 0.71 0.14 0.44 0.33 0.75 0.45 0.57 0.68 033 039 0.41 0.89 0.47 0.38 0.72 032 2.18 0.99 1.03 0.48 0.47 0.41 0.34 0.74 0.29 0.93 1.00 1.48 132 1.16 1.00 S(60) 0.48 0.36 0.38 0.43 0.35 0.30 0.49 0.38 0.45 0.30 0.43 0.50 0.37 0.63 0.35 0.37 0.40 0.40 0.35 0.56 0.51 0.38 0.47 0.31 0.35 0.23 0.37 0.47 0.43 0.36 0.31 0.46 0.56 0.34 0.46 0.37 0.58 0.55 0.43 0.55 0.43 0.24 0.60 038 0.47 0.47 0.42 038 0.42 033 0.42 1.11 1.07 1922 1996AJ 112.1903Y -1 2log R-2 Lq/Mq. Valueshaveanoveralluncertaintyof±35%.indicatedbyasteriskarethegalaxiesforwhichwedeterminedextinctioncorrections Mergers areeitherlistedinJosephandWright(1985)orpossiblyhavepolarrings,asthecaseofNGC6602146(Schweizeretal.1983). listed asFieldarenotinanyoftheothercategories.GalaxiesPairsrefertotwogalaxiescontact,orwithin~3’eachonsky.The members arefoundintheM81GrouporLeoTriplet.GalaxieslistedasVirgoofCluster(cf.KenneyandYoung1988). Col. (5)Galaxyenvironment.GalaxieslistedasIsolatedhavenoneighborswithin500km/secand1Mpcprojectedonthesky.Group edge-on. Col. (4)Galaxyinclinationindegrees,derivedfromtheratioofmajortominoraxeslistedRC2[logR(25)]orUGC,andcomputedfollowingRoberts Col. (3)MorphologicaltypefromTable1. Col. (2)Galaxyname—NGC,IC,Mrk,orArpdesignation. Col. (1)Overallmorphologicalcategory. Col. (7)Logarithmoftheratiofar-infraredluminositytomoleculargasmass,inunitsLq/Mq.Valueshaveanoveralluncertainty±35%. from imagesofthe[SIII]emission(Young,Kleinmann,andAllen1988).TheextinctioncorrectedvaluesL(Ha)/M(H2),insameunitsasthoselisted Col. (6)LogarithmoftheratioHaluminositymoleculargasmass,oryieldyoungstarsperunitmassavailablegas,inunits 1923 YOUNGETAL:STARFORMATIONINSPIRALGALAXIES taken fromtheRC2. to thenearestneighborsonskyweredeterminedusing km s)isatleast1.2Mpcdistant.Theangularseparations Col. (8)RatiooftheIRAS60to100/¿mfluxdensitiesfromTable3. in column6above,are:NGC520(-1.63),NGC660(-0.76),1068(-1.35),2146(-1.40),3034(-1.21),andArp220(-1.20). (1969). Theinclinationisgivenby:cosi=1.042{10^}—0.042.Thisformulationaccountsforthefinitethicknessofagalaxyevenwhenoriented While previousstudieshavereportedthattheratio cies forthedifferentenvironmentalgroupsdescribedabove. the NearbyGalaxiesAtlas(Tully1989),withvelocities L(Har)/^(H) andL/^#(H thatarecomparabletothe sen suchthatthenearestgalaxyonsky(within±500 tion. WefindthatbothL(Ha)L#(H)andare the Haluminosityisusedtotracehighmassstarforma- Tinney etal.1990),thisisthefirststudywhichexplores isolated galaxiesissimilartothat forthefieldgalaxies,gal- enhanced inthemergers.Interestingly,meanSEEfor efficiency ofthe mergersis4-8timeshigherthan thatofthe values forthemergers.Themean highmassstarformation axy pairs,andVirgoearly-type galaxies.Onlythelate-type star formationefficiencyasafunctionofenvironmentwhere spiral galaxiesandtheirregulars havemeanratiosofboth 1986a, 1986b;Sandersetal.1986;Solomon&Sage1988; 2IR 2 Table 5liststhemeanhighmassstarformationefficien- © American Astronomical Society • Provided by theNASA Astrophysics Data System is enhancedinmergingsystems(Youngetal. Isolated Mergers Pairs Category Galaxies (1) NGC 3690/IC694 NGC 4567/4568 NGC 4298/4302 NGC 4038/39 NGC 2798/99 NGC 7217 NGC 2146 NGC 1614 NGC 5194 NGC 7479 NGC 6240 NGC 4194 NGC 3310 NGC 660 NGC 520 Mit 231 Arp 220 Galaxy (2) SAB(r)bc pec SA(s)bc pec SB(s)ab pec SA(rs)c pec SB(s)m pec (R)SA(r)ab SB(s)c pec SB(s)a pec SB(s)a pec SA(is)bc IBm pec IBm pec SA(rs)c SB(s)c 10 pec Type Pec Pec (3) Table 4.(continued) Notes toTable4 Inc. (4) (°) 46 49 68 49 66 20 67 34 38 32 66 50 60 36 52 30 mass starformationefficiencyisenhancedbyasignificant results, basedonthemeanL/^#(H)inseveral isolated galaxysample,asmeasuredbybothL(Ha)/^#(H) boost thestarformationefficiency.Clearly,itwouldbeof high massstarsperunitofmoleculargasinspiralgal- interest tostudythemolecularandionizedgascontentofa lomon &Sage(1988)thatastronginteractionisrequiredto the pairsinoursampleisnotelevated,weagreewithSo- environmentally-selected samplesofgalaxies,thatthehigh and L/^#(H).TheHadatathereforesupporttheearlier possibility, although bynomeanstheonlyone, iscloud- examine thestarformationefficienciesasafunctionof large sampleofgalaxypairswitharangeseparationsto axies. Sincethemeanhighmassstarformationefficiencyfor appears tohaveasubstantialeffectontheglobalyieldof amount instronglyinteractingsystems.Thus,environment nism responsibleforthisenhancement isnotclear.Onesuch ciency offorminghighmassstars isenhancedinmerging systems relativetoisolatedgalaxies, althoughthemecha- strength ofthegalacticencounter. IR2 2 ir2 Merger ? Merger ? Merger ? Isolated Isolated Merger Merger Merger Merger Merger Merger Env. Pair Pair Pair Pair Pair Pair The observationspresentedhere indicatethattheeffi- (5) UHoO/MOy , -1.78 -1.83 -2.63 ’ -3.04 * -1.85 -2.11 -2.39 -1.64 -1.58 -1.90 -2.12 -1.28 -2.99 -1.62 -1.48 -0.51 -2.22 * log (6) L(IR)/M(H) 2 (L^ 0.45 0.66 0.56 0.63 0.87 0.66 0.51 0.26 0.96 0.70 1.37 1.76 1.39 1.63 1.28 1.52 1.12 log (7) S(100) S(60) 0.56 029 0.71 0.44 0.37 0.24 0.52 0.91 0.99 0.74 0.95 0.76 0.67 0.83 0.76 1.00 1.08 (8) 1923 00>H O'!o 1924 YOUNG ETAL.: STAR FORMATION IN SPIRAL GALAXIES 1924 of galaxies, may not be associated with star formation. Fur- ^0 thermore, correcting the Ha luminosities for internal extinc- tion would increase the luminosities and decrease the cycling times. Therefore, the cycling times could in fact be shorter than those indicated in Fig. 13. We note that it is also pos- sible that the cycling time will vary with radius in a galaxy, that regions with high star formation efficiency will cycle the gas in shorter times than regions of low efficiency. To verify our methodology and results, it is important to compare the gas cycling times estimated from the Ha lumi- nosity in Fig. 13 with gas cycling times estimated from the total luminosity, following Sco ville & Young (1983). Under the assumption that most of the luminosity of a galaxy is produced by O, B, and A stars, and that these stars process 13% of their mass through the CNO cycle while on the main sequence (Schwarzschild 1958), an estimate of the star for- mation rate is given by 11 SFR03,A=7.7X10- Ltot[^o/yr], (10) Fig. 11. Comparison of two measures of the star formation efficiency, that where Ltot is the total luminosity. Figure 14 shows a com- derived from the ratio of Ha luminosity to H2 mass with that derived from parison of the total luminosity, determined from the far- the ratio of the far-infrared luminosity to H2 mass. Galaxies are coded by infrared and blue bands (see Table 3), with the total mass of morphological type as indicated. Only galaxies with inclinations less than gas in molecular and atomic form. The dashed lines indicate 70° are included. the times in which the available gas will be cycled through stars given the present star formation rates. As in Fig. 13, the cloud collisions, which may lead to the formation of high majority of the galaxies have cycling times between 109 and mass stars (Scoville et al 1986), and whose rate has been 1010 years. Thus, for a 1010 year old disk, the present level of shown to be enhanced for strong galaxy-galaxy interactions star formation can be sustained into the future for a time (Noguchi & Ishibashi 1986; Olson & Kwan 1990a, 1990b). which is comparable to the current age of the disk. 5.4 Time scale for Cycling of Gas Through Stars There have been some suggestions in the literature of the 6. CONCLUSIONS depletion of gas in galaxies through star formation. This of course depends on the assumption that the low mass stars, We have obtained CCD images of 120 galaxies in the which we do not observe, form in proportion to the high light of Ha and the Æ-band continuum in order to determine mass stars according to some IMF. It is the low mass stars the distribution of star formation within spiral galaxies. which lock up mass into inert remnants, while the high mass (1) We find a small but significant variation in the mean stars are recycled into the ISM. If only high mass stars form, Ha surface brightness as a function of type for spiral galax- or if the IMF is weighted toward the high mass end, then gas ies along the Hubble sequence. The Sd-Ir galaxies have a depletion may not occur at all. For this reason, we refer here mean Ha surface brightness which is 1.4 times higher than to the gas cycling time rather than the depletion time. for Sbc-Scd galaxies, and 2-3 times higher than for Sa-Sb In Sec. 4.2 we described the relationship between the lu- galaxies. minosity in high mass stars and the quantity of gas undergo- (2) The star formation rate per unit mass of molecular gas, ing star formation [see Eq. (9)]. Additionally, Table 3 lists deduced from the global ratio L(Ha)/^(H2), shows no sig- the global interstellar masses of molecular and atomic gas. nificant variations in the mean as a function of morphologi- Therefore, we can estimate the length of time that the present cal type for the spiral galaxies with types Sa-Sc in our star formation rate can be sustained by the available supply sample. We find that this ratio varies by roughly an order of of gas, under the assumption that the star formation rate per- magnitude within each type, while the Ha luminosities for sists into the future. This gas cycling time is given by the the galaxies themselves range over four orders of magnitude reciprocal of the star formation efficiency for an adopted for the entire sample. It therefore appears that, at the current IMF. epoch, galactic disks for bright spiral galaxies are globally Figure 13 shows the global Ho? luminosity compared with converting gas into stars with roughly the same mean effi- the total amount of neutral interstellar gas mass in molecular ciency. and atomic form. The dashed lines indicate the gas cycling (3) The high mass star formation rate per unit mass of times, under the assumption of a modified Miller-Scalo IMF molecular gas is enhanced in mergers relative to isolated between 0.1 and 100 as described in Sec. 4.2. For spirals by a factor of ~4 (uncorrected for extinction). This the galaxies in this sample, the majority of the cycling times confirms earlier results based on the ratio LIRL#(H2) that fall between 109 and 1010 years. It is important to realize that the yield of high mass stars per unit mass of molecular gas is some of the neutral gas, especially the HI in the outer parts elevated in merging and strongly interacting systems. The © American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1903Y limits tothestarformationefficiency(basedonupperCOintegrated intensity).Onlygalaxieswithinclinationslessthan70°areincluded. Fig. 12.Histogramsofthestarformationefficiencyasafunctionmorphological typemeasuredfromtheratioofHaluminositytomoleculargasmass 1925 YOUNGETAL.:STARFORMATIONINSPIRALGALAXIES ties ariseindiscreteHnregionsasopposedtoactivenuclei. Tía imagesalsodemonstratethattheelevatedHotluminosi- the moleculargasmassesfor thespiralgalaxiesinour luminosity measured byIRAS.Ifoldstarsdidcontribute sig- galaxy isameasureoftherate of highmassstarformation, and thatoldstarsdonotcontribute significantlytothefar-IR sample leadstofurtherevidence thattheIRluminosityofa (left-hand panels)andfromtheratiooffar-infraredluminositytomoleculargas mass(right-handpanels).Thesolidportionofeachhistogramindicateslower (4) ThecomparisonoftheHa andIRluminositieswith © American Astronomical Society • Provided by theNASA Astrophysics Data System log [L/MJL[Lir/M Lq/Mq HaH0h larity oftheratiosL(Ha)/^(H ) andL/.yÆ(HforSaver- relative tothesystemswithsmall bulges.However,thesimi- most apparentintheearly-typebulge-dominatedsystems nificantly totheIRluminosityofagalaxy,thiswouldbe luminosity ofa spiral galaxy.i cates thatoldstarsdonotcontribute significantlytotheIR generally arisesindiscrete,identifiable Hnregions,indi- sus Scgalaxies,andtheknowledge thattheHaluminosity 2m 1925 1996AJ 112.1903Y 9 10 less than70°.Theuncertaintieslistedindicatetheaccuracyofmeanvalue. Col. (4)and(5)Meanvaluesofthestarformationefficiency,measuredinbothHaIR.Themeanslistedrefertogalaxieswithinclinations Young, Kleinmann,andAllen1988).Themergercategorywithouttheasteriskdoesnotincludethese4galaxies. categories. Galaxieswhoseclassificationincludesthedesignationpeculiarwereincluded.TheMergercategoryindicatedbyasterisk(*) 4 Col. (3)Numberofgalaxiesineachsubsamplewithinclinations<70°(seeTable4).PairsandMergerswerenotincludedthemorphologicaltype galaxies withhighextinction(NGC520,NGC660,2146,andArp220)forwhichcorrectionstotheHaluminositieswereincluded(cf. Col. (1)and(2)Characteristicsofthegalaxiesexamined. 1926 Fig. 13.ComparisonoftheglobalHa luminositieswiththetotalneutral that themajorityof thecyclingtimesfallbetween10and 10years. cated. Thedashedlinesindicatethegas cycling timesassumingthatthetotal interstellar gasmasses,withgalaxiesof differingmorphologicaltypeindi- star formationrateisderivedfromthe Ha luminosity[seeEq.(9b)].Note © American Astronomical Society • Provided by theNASA Astrophysics Data System YOUNG ETAL.\STARFORMATIONINSPIRALGALAXIES Type Morphological Environment Category (1) Mergers Mergers Virgo