1982ApJ...256..397F long beenstudiedinordertogetsomeunderstandingof © 1982.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. The AstrophysicalJournal,256:397-409,1982May15 Toomre 1972).Theseanomalousgalaxiesprovidevalu- with disturbedmorphologies(Arp1966;Toomreand galaxy evolution.Inparticular,recentattentionhasbeen bursts ofstarformationand/ornuclearactivity (Sargent andSearle1970;Huchra1977)galaxies given tolate-typegalaxies,especiallybluegalaxies (Biermann andFricke1977;LarsonTinsley1978; able testsoftheoriesthatlinkstellarandnuclearevolu- galaxies. Gastransferandtidalshocksmayinduce tion todynamicalinteractionsbetweenneighboring Biermann 1981)suggestthatnucleiofgalaxiescanbe Kronberg, Biermann,andSchwab1981;Kronberg Other recentresults(WeedmanandFeldman1980; of Seyfertgalaxiesalthoughgenerallylessluminous. the nucleiofnormalgalaxiescanbeseatlow-level Balick, andCrane1980;Heckman1981«,b)showsthat study ofacompletesamplegalaxies(Heckman, the seatofviolentburstsstarformation. activity, withemissionUnessimilartothenarrowlines Stocke 1978;Hummel1980).Arecentopticalandradio Italy. 2 3 The Hubblesequenceandthecolorsofgalaxieshave MassachusettsInstituteofTechnology. A1so fromtheIstitutodiRadioastronomia CNR,Bologna, harvard/Smithsonian Centerfor Astrophysics. © American Astronomical Society • Provided by theNASA Astrophysics Data System X-RAY OBSERVATIONSOFPECULIARGALAXIESWITHTHEEINSTEINOBSERVATORY 42_1 39 X-ray andradiofluxesluminosities.Thetoopticalfluxratiosformostofthese binary X-raysources.Thisinterpretationagreeswiththepictureemergingfromopticalandradio and irregular.Theyarechosentohavepecuharmorphologies,colors,insomecases,emission-hne morphological type. galaxies aresubstantiallyhigherthanthatofM31butstillsignificantlylowerthosethe and opticalfluxesluminositiesappearcorrelated.Anevenstrongercorrelationisfoundbetween and 10ergss.Insomecases,extendedormultipleemissionregionsweredetected.TheX-ray spectra. Thirteengalaxiesweredetectedwith(0.5-3keV)X-rayluminositiesrangingbetween10 our resultswiththoseoftheX-rayobservationsGalaxyandMagellanicClouds,wefind Subject headings:galaxies:nuclei—Seyfertstars:supernovaeX-rays:sources studies thatlate-typeblueanddisturbedgalaxiesareexperiencingsuddenburstsofstarformation. Seyfert galaxies.Thereisalsoacorrelationbetweenf/andincreasinglybluecolors,butnot that theX-rayemissioncanbeintegratedfromsupernovaremnantsandPopulationI that Seyfert-likenuclearemissionisnotthedominantmechanismofX-rayproduction.Comparing xB We reporttheresultsofanX-raysurveywithEinsteinObservatory33galaxies,mostlyspiral We discussseveralpossibleoriginsoftheX-rayemissioninlightourresults.conclude I. INTRODUCTION 123 G. Fabbiano,E.FeigelsonandZamorani’ Received 1981May1;acceptedNovember25 ABSTRACT 397 42-1 3941- pairs. Almostallthesegalaxiespresentdisturbedmor- issues, asbothactivenucleiandrapidstarformation phologies. ManyofthemareintheArpcatalog(Arp observations withtheEinsteinObservatoryof33gal- proved sensitivityoftheEinsteinObservatoryallows X-ray luminositiesof~10-10ergss(Elvisetal. X-ray emissionlocalizedinthecentralnuclearregion with L~10-ergssandthestudyof both thedetectionofnearbygalaxies(D~10-20Mpc) mal galaxies(M31,LMC,andSMC).Forsomeother which showstheopticalcolor/color diagramforthe galaxies withemissionlinenucleiandininteracting detect anybutthebrightestSeyfertgalaxieswithnuclear Until thelaunchofEinsteinsatellite(Giacconietal describe thegalaxiesinoursample.However,almostall axies, someofwhichheingroupsandinteractive can bedistinguishedfrommorediffuseemission. sion (Griffithsetal1979)wasalsosuggested.Theim- systems, thepresenceofnonthermalnuclearX-rayemis- should beassociatedwithenhancedX-rayemission. galaxies inoursurveyforwhich colorinformationis angular distributionoftheX-rayemission.Inthisway, to theopticalproperties.This canbeseeninFigure1 these galaxieshaveacommon characteristicwithrespect 1966). Nouniform,well-definedselectioncriterioncan 1979), X-rayinstrumentswerenotsensitiveenoughto 1978; Tananbaumetal1978)andtheveryclosestnor- x In thispaper,wereporttheresultsofX-ray The X-raybandprovidesanewapproachtothese 1982ApJ...256..397F 7 8 398 ble Atlassampleofnormalgalaxies(LarsonandTinsley B/B —VplanerepresentsthemeancolorsofHub- galaxies withshortburstsofstarformation(t~10yr, available. TheheavyUnecrossingdiagonallytheU— have beenreportedbyGriffiths (1979).Theobserved X-ray dataarediscussedin§ IIIandcomparedwiththe experiencing burstsofstarformation.Thisregionis the dashedline)andwithstarformationtakingplacein the theoreticalmodelsofLarsonandTinsley(1978) compatible withthelocusofMarkariangalaxies(Huchra all thegalaxiesinoursamplelieareabetween a longertime(r~5X10yr,thesolidthinUne).Almost sample andtheX-raydata are presentedin§II.The thin solidandthedashedlines,suggestingthattheyare uncorrected colorsinthisfigureforuniformitybecauseonlyafewofourgalaxiescorrectedfromtheRCBG2exist.Correcting for NGC4631, NGC772,NGC6946,andNGC2685,onlythe5—Fcolorwasavailableinliterature.Forthese,fulllinesidentify the Weedman 1978forNGC1672.ThelinesacrossthediagramarefromLarsonandTinsley1978.Foradescription,seetext. comphcated reddeningUnes(BiermannandFricke1976).ThefullcircleidentifiesthegalaxiesdetectedinX-rays.Forfourgalaxies, reddening willresultinadisplacementalongthelineindicatedbyarrow,unlesspartialispresentwhichcouldmore galaxies detectedinX-rays.ThecolorsweusearefromRCBG2formostofthegalaxies;J.P.Huchra1980,privatecommunicationNGC 1978). Theothersolidanddashedlinescorrespondto 3079, NGC3310,and4861;Bohuski,Fairall,Weedman1978for3125,Tololo941;Osmer,Smith, 1977). Prehminaryresultson afewofthesegalaxies Fig. 1.—Thegalaxiesobservedinthissurveyforwhichcolorinformationisavailableareplottedacolor-colordiagram.Weusethe © American Astronomical Society • Provided by theNASA Astrophysics Data System FABBIANO ETAL. B-V optical andradiopropertiesofthegalaxiesin§IV. listed incolumn(1).Themostaccuratepublishedposi- Discussion followsin§V. The Einsteinsequencenumbers, whichidentifytheIPC (Giacconi etal1979).TheresultsoftheEinsteinob- observed in22~1°X1fieldswiththeImagingPropor- field, arelistedincolumn(3). Columns(4)and(5)list the X-raycountsdistribution arelistedincolumn(2). tion ofthenucleuswithitsreferenceandcentroid servations aresummarizedinTable1.Thegalaxies tional Counter(IPC)onboardtheEinsteinObservatory the dateofobservation and theeffectiveexposure Thirty-three galaxies,someofthemingroups,were II. X-RAYOBSERVATIONS Vol. 256 oo LO r" © American Astronomical Society • Provided by theNASA Astrophysics Data System
Einstein Date of lo- Sequence Observation Time NH /x(0.5-3 keV) D Lx(0.5-3 keV) Extent Hardness RA, ô(1950)a Number (Year, Day) (s) Counts15 (cm-2) (ergs cm-2 s-1) (Mpc) (ergss-1) (') Ratio V ? CN —< o u~> o r-~ m , r- cN Ö Ö ö ö ö ö A A A B ON § 5 § 3W^ NO O- (U =>££ 22 ao 'rt§ "a-k- r9B «* p< I U O O o 3 a X X X X X X X X X X X oo —: vq S £? CN (N \o en 'O S-iÄ V V o EI ^ X X X X X X X X X X X eà % s^ o o o o O o o o o o o 3OC Üb rn q < «Tl q OO q q q «in en no no 3 § G" «ri tj- - ! 2 2 oo — © American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJ...256..397F N523 =Arp158IVZw45^—Brightknotandstreamer(Arp1966);mergeroftwogalaxies(ChincariniHeckathom1973). N772 =Arp78—LargespiralgalaxyperturbedbynearbyellipticalaboutthesizeofM32(Arp1964).Severalsmallergalaxieswithmuch N578—Normal galaxywithweakBalmerlines(Martin1976). N1672—Sersic-Pastoriza (1965)spiralwithresolvedemissionlinenucleus(Osmer,Smith,andWeedman1974).Possiblebroadforbidden N3073 =Mkn131Ho156b—Pairwith3079(RCBG2). N2773, N2775,N2777—Galaxiesingroup. N2685 =Arp336—EllipticalbodywithcircumgalacticringcomposedofHnregionsanddust(BurbidgeBurbidge1959). N1569 =Arp210VIIZw16—SimilartoM82.BrightHaenvelopeextendingtwicetheradiusofgalaxyandtwostarlikenuclei(Hodge N3079 =Ho156a4C55.19—Anomalousradiosynchrotronemissionandstructure(DeBruyn1977).Emissionlinenucleus(Heckman N3125 —Tololo3—Veryblue.EmissionUnenucleus.Heu4686inemission(Pensionetal1977). in acircleof2'0radiusaroundtheX-raycentroidat net counts(sourceminusbackground)typicallydetected N3310 =Arp217—BrightcompactgalaxywithHaarcandjetpointingtoit(Arp1966).Brightradiocontinuumemission(VanderKruit Tololo 9—Emissionlinenucleus.Hen4686inemission.Detectedat6cm.(Penstonetal.1977). N3991, N3994,N3995=Arp313Ho309c,b,aHaro5W523,W249—N3991hasabluenucleus(Haro1956)andradioemission N3448 =Arp205—ItcouldalsobeclassifiedasSdorSmwithaverypeculiarnucleus,eitherexhibitingstrongabsorptioninthecentral uncertainty onthecounts(1a).Inallcaseswederived energies between0.5and3.5keVthestatistical time onthegalaxyforeachfield.Column(6)gives limits ontheintensityarelisted.Column(7)lists N4038, N4039=Arp244=W245—The“Antennae.”Merginggalaxieswithlongstreamers(Arp1966;Toomreand1972) and radius. Forallthegalaxiesnotdetected,3aupper data, wecalculatedthesourcecountsfromacircleof33 N4631 =Arp281Ho442aK350a—Edge-ongalaxywithknotsofemission(Arp1966).IngroupNGC4656and4627 Tololo 41—Emission-linenucleus.StrongHa.Veryblue(Penstonetal1977). N4861 =Arp266Mkn59IZw49K362=W797—Resolvedintoknots(Arp1966).Probablynormalrotatinglatetypegalaxy (de 6946) whichshowedextentonavisualinspectionofthe (NGC 1672,NGC4038/39,4631,and surrounding the2'radiuscircle.Forfourofgalaxies the backgroundlocallyfromaannulusof6'7radius equivalent hydrogenabsorptioncolumnAduetoour N6052 =Arp209Mkn297W86—Chaoticwithloops(Arp1966).Hnregionsemissionlines(Weedman1972;Sandage1978).Very N6027 A-F=VIIZw631=W115—Seyfert’ssextet.Chainofgalaxies(Arp1966).Extendedradiosource(BurkeandMiley1973). N6454 =4C.55.33.1—Dgalaxyinacluster(Tritton1972). keV) energyrange.Thesefluxes werecalculatedfora rected fortheabsorptioninourgalaxy(0.5-3 galaxy (Heiles1975).Column(8)givesthefluxescor- N6946 =Arp294C59.31.1—Face-onspiralwithbrightHaarm(Arp1966)andradiodisk(VanderKruit,Allen,Rots1977).Five N7496—Emission linenucleus(Martin1976)withstrongUVcontinuum(Shobbrook1966).Broadlines,likeaSeyfert2galaxy(Veronet al different thermalspectrawith kT’sfrom2keVto10 the absorptioncolumnUsted incolumn(7).Theuseof thermal bremsstrahlungspectrum withkT=10keVand H Unes—Seyfert 2?(Veron,Veron,andZuiderwijck1980). coincident withthebluestregionofgalaxy(SeaquistandBignell1976). higher redshiftappearconnectedtoNGC772byluminousfilaments(Arp1970). comparable tothatofSeyfertgalaxies(SeaquistandBell1968).Inmultipleinteractingsystem(deVaucouleurs,de region oradoubleinteractinggalaxy(Bottinelli,Duflot,andGouguenheim1978).Dwarfcompanionat3'8(RCBG2). bright emissionknotsinnuclei(Rubin,Ford,andD’Odorico1970).Radioassociatedwiththecentralregionofsystem (Purton andWright1972;vanderHulst1978). Corwin 1976). Vaucouleurs andde1964;Carozzi,Chamaraux,Duflot-Augarde1974).Verybluegalaxy(Huchra1977).Emissionlines (RCBG2). Radiohaloandbridges(EkersSancisi1977).Brightradionucleus(deBruyn 1974; deVaucouleurs,andPence1974).Thermalradioemissionfromtheoverallgalaxystrongernonthermalsource blue (duPuyanddeVeny1969).Recentmergeroftwogalaxies(Duflot1976).InthesamegroupasSeyfert’ssextet(Casini,Heidmann, spectrum similartoHnregions(Alloin,Bergeron,andPelat1978). 19806). IngroupwithNGC3073andthirdanonymousgalaxy(RCBG2). and Tarenghi1979).SteepUVspectrum(Benvenuti,Casini,Heidmann supernovae detectedsince1917. 1971, 1976).Opticalemissionlines(Hnregions)(Heckman,Balick,andCrane1980). 1981). © American Astronomical Society • Provided by theNASA Astrophysics Data System Notes onIndividualEntries PECULIAR GALAXIES -1 Vaucouleurs, deandCorwin1976,here- in megaparsecs,calculatedfromtheradialvelocitiesof Tananbaum etal(1979).Column(9)givesthedistances Vaucouleurs (1979)lowerrecentestimatesofdistances keV orpowerlawspectrawithenergyspectralindexa column (10)givesthe(0.5-3keV)luminositiescorrected ranging from0.5to2.0changesthefluxesbyafactorof which thedifferenceisafactor 7and14,respectively. for theabsorptioninourGalaxy.Theuseofde after RCBG2),assumingH=50kmsMpc,and brightness andunderneathit the3alowerlimitsto for someofthegalaxiestypicallyresultsindecreasing the SecondReferenceCatalogofBrightGalaxies(de the methodsusedinevaluationofflux,see Column (11)Ustsourestimate fortheextentof two extremecasesofNGC772and4631for the luminositiesbylessthanafactorof4,exceptfor ~ ±20%atthemost.Foramoredetaileddescriptionof sources intheassumptionof aGaussianX-raysurface 0 401 1982ApJ...256..397F 39 132 421 2 method todetectsourceextension isbestsuitedtothe level) fortheremaininggalaxies maywellbeduetopoor 6946) arenotcompatiblewithasinglepointsourceat paper. TheX-raysourcenearNGC3448is1'4fromthe statistics (15to45netcounts). Wealsonotethatour mapping oftheX-raysandanaccuratecomparisonwith the 3alevel.Thelackofevidence ofextent(atthe3a galaxies withthehighestnetcountsinoursample(NGC main bodyofthegalaxy.Atpresentwecanonlycon- results. Theywillbediscussedindetailaseparate the radiodatawillbeneededtogivemorequantitative clustering inthecentralregionofgalaxy.Further radio nuclearsourceandthestrongeronecouldbe NGC 4631and6946arebothmorethan10'in NGC 6946,however,liewelloutsideofthe1'circle. used. ApplyingthismethodonanIPCobservationof extent. Toderivethesequantitiesweusedthemethod sider theidentificationofthisX-raysourceastentative. three discretesourcesordiffuseX-rayemissionregions described byHenryetal.(1979),exceptthatcounts the nucleus.NGC6946couldbeconsistentwithatleast associated withthefainterradioemissionatwestof sion regions.Thefainteroneisintheproximityof diameter andpresentacomplexdistributionofX-ray uncertainty intheIPCpositionaldetermination.The (nuclei) islessthanoraboutT,consistentwiththe it isnotpossibletosimplyaddalltheobservedspectra The correspondingluminositiesrangefrom1X10to X-ray fluxesbetween2and17X10"ergscm"s". below 1.2keV)andtheirstatisticalerrors. obtained, compatiblewithpreflightcalibration.Weused from PulseHeightAnalizer(PHA)channels>4were surface brightness.NGC4631showstwodistinctemis- centroids oftheX-rayemissionandopticalpositions 2.3 X10ergss".Sincemostsourceshavefewerthan ratios (theratioofthenumbercountsabovetothose 3C 273(astrongpointsource),a=0(77±0.01was angular separationsforNGC3448,4631,and from thegalaxydata.Column(12)listshardness this GaussiantodeconvolvetheGaussiansobtained 1569, NGC1672,4038/39,4631,and and studythecharacteristicsof“average”spectrum. IPC experiencedwidevariationsintheinstrumentgain, (V<1X 10cm").Sincethesegalaxieswereob- neither extremelysoft(kT>\keV)norcutoff which appearsrathersoft)areconsistentwithhardness study, 13aredetectedatleastthe3alevelwithsoft served atthebeginningofEinsteinmission,when ratios of~1,implyingthattheintrinsicspectraare ~80 photons,littleinformationisobtainedregarding 402 the X-rayspectra.Allbutonesource(NGC4038/39 H The X-raysurfacebrightnessdistributionsofthefive In mostcasestheangularseparationbetween Of the22individualandgroupsofgalaxiesunder © American Astronomical Society • Provided by theNASA Astrophysics Data System in. RESULTS FABBIANO ETAL. a luminosities againsteachother inFigures3band3d. ity, wehavealsoplottedtheintrinsicmonochromatic lated luminositydistributionstoshowfluxcorrelations between luminositieswhendistancecorrectionsareap- evident. Sincetheupperlimits areessentialtoestablish under specialcircumstances.Tocheckforthispossibil- plied. Atthesametime,itisalsopossibleforuncorre- plot), thepresenceofacorrelationissuggestedinboth the correlationsbetweenfluxes, nonparametricmethods From boththesetwolatter plots, correlationsarealso ing theproblemofintroducingspuriouscorrelations cases bytherelativedistributionsofdetectionsand correlations betweenfluxeshastheadvantageofavoid- emission andeithertheopticalorradioemission. spread inthepoints(especiallylog/,versuslogf and log/;*,respectively.Althoughthereisacertain Figure 3aandcshowlog/,plottedversuslog/ the upperlimits.Forfluxlimitedsamples,asearchfor radio source. is apparentfromthisfigure:TheX-raypointtendsto flatter thana0.7,suggestingthepossibilityofnuclear exception isNGC6454,wheretheradiospectrum fall closetotheextrapolationofradiospectrum.An at differentfrequenciesareavailable.Asurprisingresult composite spectraradiotoX-raysforthegalaxiesinour Throughout Table2allthemagnitudesotherthanB^, sample detectedinX-raysforwhichradiomeasurement B B are enclosedinparentheses.InFigure2,weplotthe and allthefluxesfluxratiosderivedfromthese quantity arelistedincolumn(5).Column(6)and(7)list The sourcesoftheradiodataweusedtoderivethis we extrapolatedorinterpolatedadjacentmeasurements When thisquantitywasnotavailablefromtheliterature, tively. Column(8)givestheratioofthesetwoquantities. the monochromaticBand2keVfluxes(inmJy),respec- assuming aradiospectrumofformv~with=0.7. (4) hststheradiofluxdensity(inmJy)at1400MHz. morphological parameterTfromtheRCBG2.Column When thisisnotavailable,theapparentbluemagnitude plex cases. magnitude fromothersources.Column(3)liststhe (B) fromtheRCBG2islistedor,visualorblue Table 2.Column(2)liststhebluemagnitudecorrected compatible withasinglepointsourceinthemorecom- case ofarelativelysimplesurfacebrightnessdistribu- for inclinationandreddening(Bj)fromtheRCBG2. fluxes ofthegalaxiesinoursamplearesummarized tion. Itonlygivesanindicationofthesourcenotbeing IV. COMPARISONWITHRADIOANDOPTICALPROPERTIES We havelookedforcorrelationsbetweentheX-ray The radio(1400MHz)andopticalmonochromatic a) CorrelationsbetweenX-RayandOptical X-Ray andRadioFluxesLuminosities Vol. 256 1982ApJ...256..397F No. 2,1982 log LhaveaGaussiandistributionwithdispersion cannot beusedtoevaluatetheirsignificance.Wethere- where Fwillbeeitherf,Lor.Byminimizing fore apphedaparametricmethodthatusestheinforma- tion givenbybothdetectionsandupperlimits(Y.Avni around astraightlinerelationofthetype:logF+b, the functionS=—2lnL,whereLislikelihood method (Avnieiö/.1980). error ontheparametera(which givesthesignificanceof function, theparametersa,b,andacanbederived.The 1982). Theonlyassumptionneededisthatlog/*and the correlation)canbecalculated withavariational x BR © American Astronomical Society • Provided by theNASA Astrophysics Data System 2685 2775 2773 2777 Tololo 9 3079 3073 3310 3125 4861 4631 3448 Tololo 41 4038/39 3995 3994 3991 1672 1569 6052 6946 6454 6027 A-F Van derKruitanddeBruyn1976referencestherein.(20)SeaquistBell1968.(21)Hutchmeier1975.(22)BurkeMiley 7496 Wilhs 1967.(27)Kühretal1979.(28)VanderKruit,Allen,andRots1977referencestherein. (compilation of).(16)Bohuski,Fairall,andWeedman1978.(17)Bolton,Shimmins,Wall1975.(18)Pensionetai1977.(19) Kruit 1971.(13)deBruyn1976andreferencestherein.(14)GioiaGregorini1980.(15)Seaquist,Davis,Bignell1978 McCutcheon 1973.(9)Sramek1975.(10)Wright,Savage,andBolton1977.(11)Heckman,Balick,Crane1980.(12)Vander 1980. (5)E.Hummel1981,privatecommunication.(6)Wright1974.(7)deVaucouleurs,andCorwin1976.(8) 1973. (23)PurtonandWright1972.(24)Pooley1969referencestherein.(25)TovmassianTerzian1974.(26)Caswell 523 772 578 a (NGC) Name References.—(1) SulenticandTifft1973.(2)DresselCondon1978.(3)Hummel1980.(4)Pfleiderer,Durst,Gebier To derivethesefluxesfromthemagnitudes,Johnson’stable(1966)wasused. (1) (13.5) 1 (14.0) 1 (14.5) 1 (14.0) 1 (13.55) 16 (14.74) 16- (13.35) (16.85) 16 (14.5) 1 10.58 10.65 11.13 11.51 10.63 10.85 10.43 10.90 11.59 12.26 12.97 12.86 12.24 13.03 10.88 11.25 9.03 8.49 (2) T -2 (3) -3 -5 10 3 5 2 2 3 5 /* (1400MHz) Optical, Radio,andX-RayProperties (mJy) <400 <500 <50 (4) <19 1300 1400 PECULIAR GALAXIES 420 333 850 155 250 760 175 50 28 30 37 15 45 60 80 20 27 85 TABLE 2 4.7.8.9 2.3.4.5.6 2 4,11,12 3.4 2 2.3.4.6 5,10 4,8,9,11, 3,4,8,9, 21 20 3,4,9,20 2.3.4 2,4,9,14,24 2.3.9 4,9,11,14 2,9,25 2,22 26,27 3,5,22,23 28 17 11,13,14,15 18 14,19 17 Reference 2 Radio \ogL =0.66±°ot\ogL+3M, tions and14upperlimits,weobtain: (5) x2B and For theX-rayopticalrelationships,using13detec- a= (log/x) 0.32, o(logL)=0.54. x 1084.9 1783.9 = 260.2 244.0 248.5 202.9 298.8 (mJy) 156.8 110.5 (15.3) 193.8 102.6 197.4 (13.3) 140.4 (20.4) log/* (0.37±0.10)log/—5.10, 28.8 // 31.9 27.2 55.4 56.4 B (6.1) (6) (8.2) (8.2) (3.4) (0.4) (6.0) -5 -5 -5 -5 -5 5 -5 -5 -5 -5 -5 5 -5 < 4.3X10 < 3.0X10 < 5.8X10 < 3.0X10 < 3.9X10 < 6.5X10~ < 3.9X10 < 1.5X10 < 2.2X10 < 3.9X10 <7.4X10“ < 9.1X10 < 3.2X10~ < 1.7X10 5 f (2keV) -5 -5 5 -5 -5 -5 4 -5 4 4 4 x 4.1 X10" 4.5X10 8.6X10 5.0X10" 6.9X10 3.6X10 4.4X10 1.4X10" 7.6X10 1.2X10" 1.1X10“ 1.5X10“ (mly) (7) -6 -6 5 -7 -6 6 <(1.0X < (3.7X < (6.4X < (7.9X < (5.0X10) < (1.6X10) < (5.6X10~) < 5.2X < 7.0X10 < 1.8X < 1.9X < 3.3X10 <5.3X10“ 6 < 1.4X10~ 7 -6 -7 -7 -7 7 (3.4X10“) 2.0 X 3.5X 5.3 X 6.5X10" 2.2X10 3.5X10 7.8X10 7.6X10 1.7X 1.0X10" fx/ÍB (8) 6 7 7 7 7 7 6 7 6 7 6 10“) 10~ 10“ 10" 10" 10“ 10“) 10“ 10“) 10" 10“) 403 r"h oo UD CMLO 404 FABBIANO ET AL. Vol. 256 h) a CM CO00 10e I0112 I0116 10e 10 12 I0116 10e 10 12 I0J61 FREQUENCY(Hz) Fig. 2.—Composite radio to X-ray spectra. The X-ray values are from this survey, the optical points are from RCBG2, and Sulentic and Tifft 1973. IR photometry for NGC 1672 is from Glass 1973. UV photometry for NGC 4631 is from Coleman, Wu, and Weedman 1980. For the references for the radio flux densities, see Table 2. We therefore have a 3.7 a correlation between log/* and We conclude that the X-ray emission is correlated log/# and a 3.3 o correlation between log Lx and log LB. with both the optical and the total radio emission at Similarly in the relationships with the radio emission, 1400 MHz. The correlation is much tighter in the radio using 11 detections (number of points for which both than in the optical case. Nothing can be said about any radio and X-ray fluxes and luminosities are known) and correlations of the X-ray flux or luminosity with the 10 upper limits, we obtain: nuclear radio flux or luminosity. In fact, for only three of the galaxies in our sample (NGC 3079, NGC 3448, log /* - (0.57±0.11) log/# - 5.59, and NGC 3994) has the detection of a nuclear radio component been reported (Van der Kruit 1971; a(log/jc) ~ 0.26, Huchtmeier 1975; Heckman, Balick, and Crane 1980; Hummel 1980; E. Hummel 1981, private communica- and tion). log L* = (0.76 ±0.10) log L*+0.40, b) Distribution of fx/fB © American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJ...256..397F -1 No. 2,1982 The verticalcrosshatchedarearepresents thelocusofgalaxies having thesame///#asM31.The upperlimitsareindicatedbya and thegalaxiesinthissurvey (b). Theshadedareain(a) represents theSeyfert2galaxiesand theclearareaSeyfertI’s. “ <”inthecorrespondingsquare. ergs sHz,(c)Log/,vs.log/#,(d)LogLlogL#.L#isthemonochromaticradioluminosityat1400MHzinHz“. for whichBt(fromRCBG2)isnotavailable.TheerrorbarsontheX-rayfluxesincludebothstatisticaland20%due to the uncertaintyinspectrum,(b)LogLvs.log.HereandaremonochromaticX-rayopticalblueluminosities in x xB Fig. 4.—Histogramofthelog///#forSeyfertgalaxies(a) Fig. 3.—(a)Log/*vs.log/#.Thedotsandthearrowsthatrepresentupperlimitsonfareenclosedinparenthesesforallgalaxies x © American Astronomical Society • Provided by theNASA Astrophysics Data System log fR(1400MHzKmJy) PECULIAR GALAXIES ///# withthemorphologicaltype. higher thanthatofM31.However,eightthegalaxies higher thanthatofM31.AcomparisonwiththeSeyfert galaxies (Kriss,Cañizares,andRicker1980)(Fig.4a) detected inoursurveyhave///#afactorof25ormore clearly separatedfromthatoftheSeyfert1galaxies, shows thatthedistributionof///#ourgalaxiesis limits inX-rayareavailable,have//fconsistentwith Seyfert 1galaxieshavingf/~400timeslargerinthe trary, Seyfert2galaxies,formostofwhichonlyupper average thanthegalaxiesheresurveyed.Oncon- those ofthegalaxiesheresurveyed. (U—B)t. Thegalaxiesthat havealargerX-rayto galaxy colors.Fig.6shows log///#plottedversus optical fluxratiotendalso to havethebluestcolors. The SpearmanRankcorrelationcoefficientisr= —0.08. Weobtainasimilarresultwhenwecompare the morphologicalparameterTofRCBG2(Fig.5). B xB s The ratio///#doesappear to becorrelatedwiththe There isnoevidenceofcorrelationbetween///#and c) ///#versusMorphologicalTypeandColors 405 1982ApJ...256..397F 406 points willmovesomewhattowardssmallervaluesofU—B.For not availableareenclosedinparentheses.Aftercorrection,these representing thosegalaxiesforwhichthecorrectedcolorindexis Fig. 1. limits allappeartobeconsistentwiththetrendsug- Applying theSpearmanrankcorrelationtest,weobtain references ontheU—Bvaluesusedinthisgraph,seecaptionof limits, weobtaina3correlation.Asimilarcorrelation gested bythedetections.Usingparametricmethod is suggestedbetweenf/and(B—K)£,wherewe discussed in§TVawith10detectionsandeightupper a probabilityofchanceoccurrence<1%.Theupper with themorphologicaltypeofdistortedgalaxies, obtain a6%probabilityofchanceoccurrence. observed colorsofthegalaxiesandthosefornormal of the“colorexcess”,i.e.differencebetween reddening. If,however,weuse themorphologicaltypes not aneasytaskbecauseoftheuncertaintiesassociated field galaxiesofthesamemorphologicaltype.Thisis morphological type(Huchra 1977), wefindthatforthe spread incolorsoffieldgalaxies, andtheintrinsic as reportedonTable2andthe averagecolorsforeach xB Fig. 6.—Logof//^versus(U—B)j(RCBG2).Thepoints We alsoinvestigatedthebehavioroff/infunction x xB © American Astronomical Society • Provided by theNASA Astrophysics Data System Fig. 5.—Logoff/vs.themorphologicalparameterT(RCBG2) xB FABBIANO ETAL. 6-7 36-1 detected galaxieswhosetotaldeviation(towardtheblue) mag (f/f~T5X\0comparedto3.7X10). from theaveragecolorsisA>0.5magratiof/ X-ray andtotalopticalemissionbetween about 3timesthatofthedetectedgalaxieswithA<0.5 lanic Cloud(SewardandMitchell1981),isdominated emission, theyshowthatinquiteafewcasesnuclear clude thepresenceofanuclearcomponentX-ray of aSeyfert2nucleushasbeensuggested(Veron,Veron galaxies detectedinoursurvey,NGG1672,thepresence could inducenuclearactivity.Moreover,foroneofthe associated neighboringgalaxies(Table1).Statistical lar clusters,binarysystemsandrelativelyyoung by asmallnumberofdiscretebrightsources,likeglobu- nuclear originoftheX-rays. radio emission(whichisprimarilydiskinthese flux, asevidencedbyourresultsontheangularextentof emission alonecannotexplainthewholeofdetected and Zuiderwijck1980).Althoughourdatacannotex- studies ofradioemissioningalaxiessuggest(Stocke Large MagellanicCloud(LongandHelfand1979;Long, galaxies likeM31(VanSpeybroecketal.1979),the galaxies) (§IVa)furthersuggestadiskratherthan Helfand, andGrabelsky1981),theSmallMagel- the X-raysources(§III).Thecorrelationsbetween metallicity, SNRsareresponsible for—10%ofthetotal observed inX-rayswithL^^IO^-IO ergss.Inthe Population IIobjects,wouldnotgiverisetotheob- LMC, whichmightbetterresemble thelate-typepecuhar sample. AnumberofSNRsinourGalaxyhavebeen served relationshipbetweenf/andbluecolorsinour supernova remnants(SNR).Globularclusters,being galaxies becauseofitsmorphological typeandlow 1978; Hummel1980)thatthepresenceofacompanion xB xB xB The X-rayemissionofourgalaxyandnearby Most ofthegalaxiesdiscussedinthispaperhave b) IntegratedEmissionofDiscreteGalacticX-Ray a) NuclearActivity V. DISCUSSION Sources Vol. 256 1982ApJ...256..397F 6 37-1 371 -1 39_1 4041-1 4 3891 78 5 389 No. 2,1982 fx/fe ~lO-MO“forOstars fromtheresultsofVaiana lifetime r—5000yrforyoungSNRs,assuggestedbythe X-ray emissionandaremoreluminousthanthoseofthe decay oftheirX-rayluminositywithtime(Gorenstein, with perturbedmorphologicalappearancemightexperi- five supemovaehavebeenobservedinthelast100years Hamden, andTucker1974;seealsoLongHelfand contribution ofolderSNRswillnotbeasimportant order toproduceanintegratedX-rayluminosityof LMC observationsofLongandHelfand(1979),20-200 Milky Way.ForanaverageL^IOergssanda likely thatSNRsmightaccountforasubstantialfrac- not beunreasonable(seealsoTammann1978).Itisthen regular morphology.Othergalaxiesfarmoreblueand colors thanmostgalaxiesinoursurveyandafairly (RCBG2; Wild1980).Thisgalaxy,however,hasredder the contributionofyoungeronesduetorapid supernova explosionspercenturywouldbeneededin both inourGalaxy(withL~10ergss“)andthe black hole),havebeenidentifiedasstrongX-raysources galaxies, althoughhigherthaninnormalwould ence acomparableorhighersupernovarate.Therefore, infrared observationsofNGC6946(TelescoandHarper A similarnumberofOBstarscanbeinferredfrom violet IUEobservationsofNGC6052(Mkn297),one weaker, softX-rayspectmm(Shulmanetal1975).The binaries typicallyhaveflatspectraathighenergies,they a supernovarateof10-20percenturyinlate-type ^ iQ40-41g-ifgjgalaxy.Theintegrated Population Ibinarysystems,inwhichtheprimaryisan of theX-rayemissionlate-typepeculiargalaxies. X-ray luminosities. of binaries~200andanintegratedX-rayluminosity ergs sforeachbinaryX-raysource(byanalogywith of thegalaxiesinoursurvey,suggestthatthisgalaxyhas emit ~3X10ergssbetween0.15and0.8keVwith can havesoftX-rayexcesses.SMCX-lisreportedto Magellanic Clouds(wheretheycanhaveL^’sashigh OB supergiantandthesecondaryaneutronstar(or the wholeofit. tion oftheX-rayemission,althoughprobablynotfor integrated X-rayoutputof the normalPopulationI L ~2X10“ergsscomparabletothedetected the LMCsources),wecanthereforeestimateanumber a spectmmofkT=03keVor—3.5(Bunnerand type binaryX-raysources(vandenHeuvel1980).Ultra- Sanders 1979).HerculesX-lhasasimilar,though 1979) .Inoneofthegalaxiesoursurvey,NGC6946, ~ 10OBstarsinourownGalaxyproduce20early- -10-10 ergss“[Clarketal1978]).AlthoughX-ray et al(1981),10-10Ostars wouldbeneededtoattain stellar contentofthegalaxies. Infact,evenifweobtain ~ 10OBstars(Benvenuti,Casini,andHeidmann1979). x 1980) .Assuming atypicalX-rayluminosityof~10 erS soraven x Binary systemsarelikelytobethemaincomponent We canexcludeasignificantcontributionfromthe © American Astronomical Society • Provided by theNASA Astrophysics Data System PECULIAR GALAXIES 41- 37 1 -13 6 38_ 14 6 7 -6 actual numberofearlystarsinthesegalaxies. two ordersofmagnitude(ormore)higherthanthe an integratedL^IO^-IOergss.Thisisprobably lated withgalaxycolors(Tamman1978)inthesame massive PopulationIprogenitors)appearstobecorre- rate ofTypeIIsupernovaevents(whichoriginatefrom and thecorrelationbetweenf(Fig.6)tendto are responsibleformostoftheX-rayemission.Also, support thehypothesisthatSNRsandbinarysources quantity intheX-rayband(foraSNRwithL—10 (Biermann andFricke1977),calculatingasimilar total timeintegralofnonthermalradiocontinuumradia- sense asthef/.Assuming10“Jyyrat5GHz yr (vandenHeuvel1977).Inthiscase,however,the ergs s,t~5X10yr),weobtainaratiooftheX-ray tion comingfromasupernovaremnantat20Mpc to theradiofluxf/—2X10“.Wecanperforma calculation isevenmoreuncertainbecausewehaveto similar calculationinthecaseofX-raybinaries, X-ray binariesandsupemovaeusingourowngalaxy assuming an^10ergssandalifetimer«4X10 binaries impliesasupernovarateof10-30percentury. scale fortheX-raybinaryformationrateversus Then, withthetypicalparametersforSNRsandbinaries supernova rate,sinceweassumethattheradiooutputis our sample.However,giventhelargeuncertaintiesin Both thesevaluesoff/arehigher(byfactors4to as normalization,theexpectednumberof200X-ray always duetoSNRs.Assumingproportionalitybetween may notbesignificant.Ontheotherhand,ifwetake difference betweentheexpectedandobservedf/ as givenabove,wecancalculatearatio/^//^—5X10~. blackbody radiationortheopticalphotonfieldof radio flux,andadifferentemissionmechanismisre- of theX-rayemission,thennonthermalradioemis- xR off theradiophotonswouldgiveinallcasesfluxes radio andopticalradiationfromMarkariangalaxies. quired. AsimilarconclusionwasreachedbyBiermann sion fromSNRscannotberesponsibleforthetotal suggest that,ifsupemovaeandbinariescontributemost these highervaluesoff/attheirfacevalue,they the assumedparametersbothinradioandX-ray, ones. InverseCompton,offthebackground3K several ordersofmagnitudesmallerthantheobserved and Fricke(1977)inastudyabouttheoriginof bution oftheinverseCompton radiationcouldbeonlya netic fieldis£~10“gauss. For amorelikelyvalueof galaxies, couldcontributesignificantlyonlyifthemag- x xB xR few percentofthetotal.We cansetlowerlimitsof the magneticfield,likeZ?^3X10 gauss,thecontri- 10) thantheaverageratioobservedforgalaxiesin xR xR xR The integratedspectraofthepeculiargalaxies(Fig.2) The inverseComptonscatteringoftheradioelectrons c) OtherX-RayProductionMechanisms 407 1982ApJ...256..397F -7 -6 104 174 4 3942-1 optical photons. 772 andNGC6052fromtheComptonscatteringoff 408 from radiotoX-rayscouldbesuggestedbythefactthat ~ 3X10gaussontheaveragemagneticfieldofNGC less thanthecosmicraylifetimeindiskof yrifi?^3X10 gauss,abouttwoordersofmagnitude radio spectrum(Fig.2).However,theelectronsynchro- the X-rayfluxestendtofallonextensionof power law,thesynchrotronlosseswouldsteepenit injection spectrumbetween10andeVisasingle higher energycosmicrayelectronstakesplaceontime ble totheobservedfluxesonlyifreaccelerationof contribution attheX-rayconsiderablybelowob- considerably atthehigherenergies,givingasynchrotron Galaxy (Wentzel1974).Thisimpliesthatiftheelectron tron lifetimeatX-rayfrequencies(~10Hz)is~10 possible haloorigin. X-rays originatefromthecentralregionofgalaxy detection level.InNGC4631and6946inparticular,the most caseswithpredictedX-rayluminositiesbelowour exist aroundspiralgalaxies(NormanandSilk1979),in scales <10yr. served value.TheX-raysynchrotronwouldbecompara- and appearsufficientlyclumpytocastdoubtsona photon countshowevidenceofextendedormultiple galaxies arethefollowing: emission regions. ..1966,Ap.J.Suppl.123,14,1. .1970,Ap.J.{Letters),5,L57. Arp, H.1964,Ap.J.,139,1045. Alloin, D.,Bergeron,J.,andPelât,D.1978.Astr.Ap.,70,141. Avni, Y.1982,inpreparation. 10-10 ergssrange.Thegalaxieswiththehigher Avni, Y.,Soltan,A.,Tananbaum,H.,andZamorani,G.1980,Ap. Benvenuti, P.,Casini,C,andHeidmann,J.1979,Nature,282,272. Bunner, A.N.,andSanders,W.T.1979,Ap.J.{Letters),228,L19. Bohuski, T.J.,Fairall,A.P.,andWeedman,D.W.1978.Ap. Biermann, P.,andFricke,K.1977,Astr.,4/?.,54,461. Burke, B.F.andMiley,G.K.1973,Astr.Ap.,28,379. Burbidge, E.M.,andG.R.1959,Ap.J.,130,20. 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