Mon.Not.R.Astron.Soc.317,667–686(2000) An Ha survey of eight Abell clusters: the dependence of tidally induced star formation on cluster density C. Moss1w and M. Whittle2 1VaticanObservatoryResearchGroup,StewardObservatory,UniversityofArizona,Tucson,AZ85721,USA 2DepartmentofAstronomy,UniversityofVirginia,Charlottesville,VA22903,USA Accepted2000May1.Received2000March1;inoriginalform1999November30 D o w n lo ABSTRACT a d WehaveundertakenasurveyofHaemission inasubstantiallycompletesampleofCGCG ed galaxiesoftypesSaandlaterwithin1.5Abellradiiofthecentresofeightlow-redshiftAbell fro m clusters (Abell 262, 347, 400, 426, 569, 779, 1367 and 1656). Some 320 galaxies were h surveyed, of which 116 were detected in emission (39 per cent of spirals, 75 per cent of ttp s peculiars). Here we present previously unpublished data for 243 galaxies in seven clusters. ://a c Detected emission is classified as ‘compact’ or ‘diffuse’. From an analysis of the full ad e surveysample,weconfirmourpreviousidentificationofcompactanddiffuseemissionwith m ic circumnuclear starburst and disc emission respectively. The circumnuclear emission is .o u associated either with the presence of a bar, or with a disturbed galaxy morphology p.c o indicative of ongoing tidal interactions (whether galaxy–galaxy, galaxy–group, or galaxy– m /m cluster). n The frequency of such tidally induced (circumnuclear) starburst emission in spirals ras /a increasesfromregionsoflowertohigherlocalgalaxysurfacedensity,andfromclusterswith rtic lowertohighercentralgalaxyspacedensity.Thepercentagesofspiralsclassedasdisturbed le -a and of galaxies classified as peculiar show a similar trend. These results suggest that tidal b s interactions for spirals are more frequent in regions of higher local density and for clusters tra c with higher central galaxy density. The prevalence of such tidal interactions in clusters is t/3 1 expectedfromrecenttheoreticalmodellingofclusterswithanon-staticpotentialundergoing 7/3 collapse and infall. Furthermore, in accord with this picture, we suggest that peculiar /66 7 galaxies are predominantly ongoing mergers. /9 6 We conclude that tidal interactions are likely to be the main mechanism for the 73 7 transformation of spirals to S0s in clusters. This mechanism operates more efficiently in 1 b higherdensityenvironments,asisrequiredbythemorphologicaltype–localsurfacedensity y g u (T–S) relation for galaxies in clusters. For regions of comparable local density, the e s frequency of tidally induced starburst emission is greater in clusters with higher central t o n galaxydensity.Thisimpliesthat,foragivenlocaldensity,morphologicaltransformationof 0 4 discgalaxiesproceedsmorerapidlyinclustersofhighercentralgalaxydensity.Thiseffectis Ap considered to be the result of subcluster merging, and could account for the previously ril 2 0 considered anomalous absence of a significant T–S relation for irregular clusters at 1 9 intermediate redshift. Key words: stars: formation – galaxies: clusters: general – galaxies: evolution – galaxies: interactions – galaxies: spiral. Humason1931;Oemler1974).Morerecently,datafromtheHST 1 INTRODUCTION haveshowntheremarkablechangesinclustergalaxypopulations The systematic differences in morphology between field and between intermediate redshifts (cid:133)z,0:5(cid:134) and the present. Inter- clustergalaxypopulationshavelongbeenknown(e.g.Hubble& mediate-redshift clusters contain a large population of blue, star- forming galaxies, which have been shown to be predominantly wE-mail:[email protected] normal spiral and irregular galaxies, a fraction of which are q2000RAS 668 C. Moss and M. Whittle interacting or obviously disturbed (e.g. Butcher & Oemler 1978; (Paper III). Here we utilize data for all eight clusters in our Dressleretal.1994;Oemler,Dressler&Butcher1997;Smailetal. sample, and do a comparable analysis for a full range of cluster 1997).Theyconstituteupto50percentoftheclusterpopulation, types, discussing how emission varies across a range of butbythepresentepochhavebeendepletedbyafactorof2inrich environments of differing galaxy densities. We also attempt to clustersandhavebeenreplacedbyacorrespondingincreaseinthe differentiate the dependence of emission on local galaxy density S0 population (Oemler1974;Dressler1980;Dressleretal.1997). fromthatonclustertype,togivefurtherinsightintoevolutionary Whatprocessesareresponsibleforthisrapiddepletionofthespiral mechanisms operatingoncluster spirals. populationandcorrespondingincreaseinS0sinrichclusterssince The paper is set out as follows. In Section 2 we describe the z(cid:136)0:5? There have been many suggested mechanisms, either to survey sample and summarize observational and emission detec- removegasand/ortoinducestarformation,someofwhichdepend tion methods. A previously unpublished list of emission-line on galaxy–galaxy collisions (e.g. Spitzer & Baade 1951; Miller galaxies (ELGs)detected forsixoftheeightsurveyedclustersis 1988; Valluri & Jog 1990), or on the effect of the intracluster giveninSection3.Inthissectionwealsoconsidertherelationof medium(e.g.Gunn &Gott1972;Cowie&Songaila1977),oron emissiontogalaxyproperties,andshowthatcompactanddiffuse D tidal shocks whether from galaxy–galaxy or cluster–galaxy inter- emission detected on the prism plates can be well understood as o w actions (e.g. Noguchi & Ishibashi 1986; Lavery & Henry 1988; circumnuclearstarburstandnormaldiscemissionrespectively.In n Sandersetal.1988;Henriksen&Byrd1996;Mooreetal.1996). Section4,usingavarietyofcluster/fieldparameters,weshowthat loa d Nearby rich clusters have a residual population of spiral there is a systematic enhancement of tidally induced starburst e d galaxies.Ifoneorseveraloftheproposedmechanismshavebeen emission with increasingly rich clusters. For the richest clusters fro operating to transform spirals into S0s over the relatively short thisenhancementisgreaterthanwouldbeexpectedsimplyonthe m h look-back time to z(cid:136)0:5; it is clear that we might expect the basis of increasing galaxy density alone. These observational ttp sreasmideupalropcoepsuselastitoonboefcsopnitrianlusiinngctlousotepresr.atTehiensethperopcreessseenstcoanntbhee rpersouvlitdseacroenvdiinscciunsgseedvidinencSeecthtiaotnsp5i,rawlshhearveewbeeenshtroawnsftohramtetdhetyo s://ac a more easily studied in nearby clusters than at higher redshifts. S0s in clusters predominantly by tidal forces, a picture fully in d e Furthermore, all of the proposed mechanisms involve potentially accordwiththemostrecentnumericalsimulationsofclusters(e.g. m ic dramatic changes in the star formation rates in spirals. Thus a Gnedin 1999). We further discuss how the observational results .o u comparison of star formation rates between spirals in nearby can explain the apparently anomalous result for type–galaxy p .c clusters and those in the field may provide the observational surface density relation found by Dressler et al. (1997) for low- o m evidence to help decide the physical mechanism which has been richness clusters at intermediate redshifts. A summary of our /m responsible for the dramatic recent change in the cluster disc resultsisgiven inSection 6. nra galaxy population. s/a In practice, it has proved difficult to establish agreement rtic amongstdifferentauthorsregardingchangesofstarformationrate le -a between field and cluster spirals. However, much recent work 2 OBSERVATIONS AND MEASUREMENTS b s supportseithersimilarorenhancedstarformationinclusterspirals tra 2.1 Clusterand galaxysamples c comparedtofieldspirals(e.g.Donasetal.1990;Moss&Whittle t/3 1993,hereafterPaperII;Gavazzi&Contursi1994;Bivianoetal. Table1givesbasicdatafortheeightAbellclustersinoursurvey 17 1997; Moss, Whittle & Pesce 1998, hereafter Paper III; Gavazzi (Abell 262, 347, 400, 426, 569, 779, 1367 and 1656). These /3/6 et al. 1998). Biviano et al. have suggested that earlier studies clustersconstitutearepresentativesample,comprisingallbuttwo 67 whichclaimedreducedstarformationinclusterspiralsmayhave ofthe10Abellclustersinthenorthernhemispherewithredshifts /96 7 beenaffectedbyanunrecognizedbiaswherebyfaintfieldgalaxies lessthan7200kms21(theothertwoclusters,Abell189and194, 3 7 are more likely to be detected in emission than their cluster are both relatively poor clusters comparable to Abell 262, 347, 1 b counterparts. Two recent studies (Balogh et al. 1998; Hashimoto 569and 779). y g etal.1998)havefoundasuppressionofstarformationincluster Our initial sample of galaxies comprised all CGCG galaxies ue s galaxies relative to galaxies of similar morphological type in the (Zwicky et al. 1960–1968) within 1.5 Abell radii of the cluster t o field. However, the morphological classifications in these studies centres(759galaxies,whereresolveddoublegalaxiesarecounted n 0 arebasedonbulge-to-discratio,anditisnotcleartowhatextent as two). These galaxies were morphologically classified (see 4 A theresultsareaffectedbythevariationofS0/Sratiofromthefield Section2.3.2)andasubsetdefinedwhichexcludedgalaxieswith p to the cluster (see Section 4.1.1 below for further discussion). Hubble types E, E/S0, S0 and S0/a, or galaxies of indeterminate ril 2 0 Furthermore, it isalso increasingly evident that star formation in type(292galaxiesremaining).Afurther28spiralsfallingbeyond 1 9 the spiral discs and in the circumnuclear region may have very 1.5Abellradiiwereincluded(27inAbell1367,oneinAbell400), different dependencies on environment (cf. Paper III; Hashimoto yieldingafinaltotalof320galaxiesselectedforthesurveyforHa etal.1998). emission. Our restriction to CGCG galaxies reflects the fact that We have made an extensive survey of Ha emission as an our detection efficiency decreases sharply below the CGCG indicator of the star formation rate in spirals in nearby clusters magnitudelimitm (cid:136)15:7;andourexclusionofE,E/S0,S0and p (Paper III, and references therein). One motivation is to under- S0/agalaxiesreflectsthefactthatinpracticetheseHubbletypes stand how the cluster environment affects the evolution of spiral are rarely detected in Ha(see Paper III). In the case of double galaxies, including the dramatic depletion of cluster spirals over galaxies, those 11 individual members fainter than 15.7 were thepastfewgiga-years.Oursurveytechniquecandistinguishwell excluded from the statistical sample, as were 15 galaxies which, betweendiscemissionandcircumnuclearstarburstemission,and for various reasons, were visible on only one of our two plates. accordinglywecaninvestigatehowthesevarywithenvironment. Thus our final statistical sample represents a substantially In previous work we have discussed in detail a comparison completegroup of potentially detectable star-forming galaxies in betweenemissioninfieldspiralsandasinglecluster,Abell1367 and aroundnearbyAbell clusters. q2000RAS,MNRAS317,667–686 Hasurvey of Abell clusters 669 Table1.ClustersincludedintheHasurvey. Cluster Clustercentre Abellradius z s n o v R.A.(1950)Dec. l b (arcmin) (kms21) Abell262 1h 49m:9 358 540 1368:59 2258:09 105 0.0163 494 47 Abell347 2 22.7 41 39 141.17 217.63 91 0.0189 582 21 Abell400 2 55.0 5 50 170.25 244.93 72 0.0238 610 71 Abell426 3 15.3 41 20 150.39 213.38 96 0.0179 1277 114 Abell569 7 5.4 48 42 168.58 22.81 88 0.0196 444 12 Abell779 9 16.8 33 59 191.07 44.41 75 0.0230 472 24 Abell1367 11 41.9 20 7 234.81 73.03 80 0.0214 822 93 Abell1656 12 57.4 28 15 58.09 87.96 74 0.0232 880 226 Cluster centres are taken from Abell, Corwin & Olowin (1989). Cluster mean redshifts, z, and velocity o dispersions, s, based on a total of n redshifts, are taken from Struble & Rood (1991), where z has been v o D correctedtothecentroidoftheLocalGroupfollowingRC2(deVaucouleurs,deVaucouleurs&Corwin1976). o TheAbellradiusisdefined(Abell1958)as5:13(cid:2)105=cz arcmin;andcorrespondsto,1.5h21Mpc,whereh w o n istheHubbleconstantinunitsof100kms21Mpc21. lo a d e d Table2.Platematerial. fro m Plateno. U.T.date Cluster Platecentre Prism Filter Exp. Tel. h R.A.(1950)Dec. (min) (E/W) ttp s 15204 1984Nov4 Abell262 1h 50m:0 358 440 2(cid:135)4 RG645 60 E ://a c 15205 1984Nov4 Abell262 1 50.2 36 13 2(cid:135)4 RG645 60 W a d 13046 1981Dec16 Abell347 2 21.9 41 20 10 RG630 120 W e m 14559 1983Oct29 Abell347 2 24.7 41 36 10 RG645 120 E ic 15198 1984Nov2 Abell400 2 55.5 6 23 2(cid:135)4 RG645 120 W .o u 15201 1984Nov3 Abell400 2 56.4 5 32 2(cid:135)4 RG645 90 E p 15191 1984Oct31 Abell426 3 16.8 41 30 2(cid:135)4 RG645 120 W .co 15195 1984Nov1 Abell426 3 15.7 41 26 2(cid:135)4 RG645 120 E m 15196 1984Nov1 Abell569 7 4.9 48 28 2(cid:135)4 RG645 120 E /m n 15230 1984Dec31 Abell569 7 5.9 48 57 2(cid:135)4 RG645 97 W ra 14078 1983Apr4 Abell779 9 17.3 33 56 10 RG630 70 E s/a 14193 1983May1 Abell779 9 16.2 33 47 10 RG630 120 W rtic 14077 1983Apr3 Abell1367 11 37.9 19 59 10 RG630 75 E le 14200 1983May3 Abell1367 11 41.9 20 00 10 RG630 120 W -a b 15270 1985Apr11 Abell1656 12 58.4 27 58 2(cid:135)4 RG645 120 E s 15271 1985Apr11 Abell1656 12 57.4 28 21 2(cid:135)4 RG645 120 W tra c t/3 1 7 2.2 Plate material andHadetection spectrawereinspectedforsignsofHaemission,whichappearsas /3/6 anHaimagesuperposedonthedispersedcontinuumspectrum.In 67 Table 2 gives basic information about the objective-prism plates PaperIIIweanalysedtheHasensitivitylimit,andfoundthatthe /96 7 usedforthesurvey,whileFig.1showsthedistributionofCGCG objective-prism technique is 90 per cent complete down to an 3 7 galaxies within the Abell clusters, as well as the objective-prism equivalentwidthlimitof20A˚ fortheHa1(cid:137)Nii(cid:138)blend,and,29 1 b plate boundaries(see PaperIII forAbell 1367). percent efficient belowthis limit. y g Our survey technique and methods have been described in Table4givesthesurveyedgalaxiesandHadetectionsforseven ue s detail in Paper I (Moss, Whittle & Irwin 1988), and to a lesser clusters,whilePaperIII givethese fortheeighth,Abell 1367. t o extentinPapersIIandIII.Herewebrieflyreviewthemethods.All n 0 plates were taken on the 61/94-cm Burrell Schmidt telescope at 2.3 Parameters andranking 4 A Kitt Peak in conditions of good seeing and transparency, and p are consequently of good quality. The plates cover approxi- Our statistical analysis requires a range of parameters to ril 2 0 mately58at94arcsecmm21anduseanemulsion/filtercombina- characterizegalaxymorphology,Haemission,localenvironment, 1 9 tionofeitherIIIaF/RG630(round)orIIIaF/RG645(square),giving andmoreglobalenvironment.WelisttheseparametersinTable3, ,350A˚ bandpass centred on 6655A˚ with a peak sensitivity together with their quantification as ranked and/or binned data ,6717A˚. Two prisms were used, either a high-dispersion 108 suitable for the non-parametric statistical tests used below prism giving ,400A˚ mm21, or, when this became unavailable, (Sections 3.1 and following), and the sample number, n, for a lower dispersion 28148 prism combination giving ,780A˚ each rank or bin. A more detailed description of individual mm21. In Paper III we compared the Hadetection efficiency of parameters isas follows. these two prism combinations, and concluded that they were substantiallyequivalent.Eachclusterwasobservedtwice,withthe 2.3.1 Haemission telescope east and west of the pier to reverse the dispersion direction.Havingtwosuchplatesnotonlyensuresamorereliable For each detected galaxy, the Ha emission was graded for detection of Ha, but also, from the difference in location of the visibilityonafive-pointscale(S – strong;MS – medium-strong; emission, yieldsrelativelyaccurate measurements ofredshift. M – medium; MW – medium-weak; and W – weak). Similarly, Using a low-power binocular microscope (,12(cid:2)), the galaxy the appearance of the Haimage was classified on a five-point q2000RAS,MNRAS317,667–686 670 C. Moss and M. Whittle D o w n lo a d e d fro m h ttp s ://a c a d e m ic .o u p .c o m /m n ra s /a rtic le -a b s tra c t/3 1 7 /3 /6 6 7 /9 6 7 3 7 1 b y g u e s t o n Ffililgeudresq1u.aCreG,CmG(cid:136)ga1la1x:1ie–s1i2n:0c;luospteernfsieqludasr.eG,malax(cid:136)y1sy2m:1b–o1l3s:0a;refitlhleedsacmircelea,smZw(cid:136)ick1y3:e1t–a1l4.:(01;9o6p0e–n19c6ir8c)l:e,crmoss(cid:136)su1p4e:r1i–m1p5o:0se;dopoennatrfiiallnegdles,qumare(cid:136),m1p5:#1–1115::07;: 04 A p p p p p p Plateboundariesareshownschematicallywithdashedlines.Thesolidanddottedlinesarecirclesofradiusr(cid:136)1:5rAand3.0rArespectively,centredonthe ril 2 clustercentre.NotethatCGCGgalaxiesareshownonlyforr#3:0rA. 01 9 scale (VC – very concentrated; C – concentrated; N – normal; (‘?’ in Table 4). We also choose binary ranks for the Ha D – diffuse; and VD – very diffuse). Concentrated emission is appearance,yieldingtwoparameters:compactemission(concen- much brighter than the underlying continuum and is sharply tration classes VC, C, or N); and diffuse emission (concentration delineated from it; diffuse emission is only slightly brighter than classesDorVD).Astrophysically,weassociatecompactemission the continuum and has an indistinct appearance, and in general with a circumnuclear starburst, and diffuse emission with more spans a larger region than the concentrated emission (for further normalongoingdisc-widestarformation.(Forfurtherdiscussion, discussion,seePaperII).Galaxieswithdouble,multiple,oroffset seeSection 3.7below.) emission were categorized as compact emission, principally because of its high surface brightness. The combined mean 2.3.2 Hubble types emissionclassificationsfromeachplatepairarelistedincolumns 12and13of Table 4. Because star formation rates depend quite sensitively on Hubble We choose a binary rank for Ha detection, with no rank type, it is important to estimate these types accurately, so that assigned for galaxies not satisfactorily surveyed for emission dependence on environment can be clearly distinguished from q2000RAS,MNRAS317,667–686 Hasurvey of Abell clusters 671 Table3.Parametersusedinthestudy. early-type galaxies, and accordingly it was decided also to omit themfromthestudy,asmentionedinSection2.1.Thesegalaxies Categories Rank/[Binno.] n should not be confused with ‘peculiar’ galaxies, nor with spirals withpostfix‘pec’,bothofwhichhavebeenretainedinthesample. Emission … 1 180 TheHubbletypeswerereducedtoeight-categorybinneddataas S,(S),MS,M,MW,W,(W) 2 115 showninTable3,andthespiralstagehasbeengivenasimplerank of 1–6. The rank assigned is independent of bar designation or CompactEmission whether‘pec’isappendedtotheclass,butnorankisassignedifa …,D,VD 1 236 spiral has no stage assigned or the galaxy is classed simply as VC,C,N,DBL 2 58 ‘Peculiar’. DiffuseEmission …,VC,C,N,DBL 1 238 D,VD 2 56 2.3.3 Barred structure D Type Since galaxy bars may be related to star formation and o w SSaab 12,,[[12]] 6320 environment, we attempted to assign bar designations for all nlo Sb 3,[3] 49 galaxies, following the de Vaucouleurs system. Unfortunately, ad e Sbc 4,[4] 17 many UGC types do not distinguish between a non-barred spiral d Sc 5,[5] 36 (e.g., SAa) and a spiral with no bar designation (e.g., Sa). fro m Sc–Irr,Irr 6,[6] 18 Accordingly, we inspected all galaxies for signs of a bar and, h S [7] 21 wherepossible,assigned abartype(e.g., SA,SAB,orSB).This ttp Peculiar [8] 62 s bar classification was included in the type descriptions of the ://a Bar galaxies inthesamplegiven incolumn 7 ofTable 4. ca A,A: 1 37 Thebarclassificationsformaranksequence(1–4;seeTable3) de AB,AB: 2 18 m from unbarred (A, A:), through intermediate (AB, AB:), to ic BB: 34 2512 uncertainbar(B:)anddefinitelybarred(B).Galaxiesforwhichno .ou p bardesignation canbe made are notassigned a rank. .c o Disturbed m … 1 210 /m D:: 2 30 2.3.4 Disturbance nra D: 3 34 s D 4 18 We have attempted to classify galaxies on the basis of whether /artic they appear disturbed or not (Table 4, column 8). Clearly, this is le Companion importantasapossiblelinktostarformationandenvironment.We -a …,[C::],[C:],[C] 1 203 b s C:: 2 2 adopted a 1–4 rank system, which corresponds to the degree of tra C: 3 18 disturbance (… [no disturbance], D::, D:, D). In assigning c C 4 25 disturbanceclass,informationwascombinedfromUGCdescrip- t/31 7 tionsandourinspectionofdirectplatematerial.Ratheruncertain /3 /6 dependence on Hubble type. Unfortunately, at redshifts of signs of galaxy disturbance (e.g., slight distortion of outer arms, 67 ,6000kms21 the cluster galaxies are quite small and difficult somewhat asymmetric appearance) are assigned D:: (rank 2); /96 moredefinitesignsofdistortion(e.g.,slightwarps,probabletidal 7 totypeaccuratelywithoutgoodplatematerial.InthecaseofAbell 3 1p(s3eer6ef7oPrwmapeetihrnedIIetIey)d.piFhnoagrvoethfeexmocoethsltleeronfctlptuhlsaetteeCrsmGtCahtiGesriigasal,nlaaoxntidethsseoincwatesheau,tsaecndlduistwtetoer psfeilgauntmuifreiescs,a,nsotolnymgodeiinstdguirsmbtueerdrbgagenar)claeax)rieeascre(laes.gass.e,sdibgaandsedDdisD(troa:rntik(oran4ns),k.sNt3roo);nrgawntkihdialiesl 71 by gue given to the few galaxies for which it is not possible to decide s httgyyaappvlaieenx.giaeF.dsooForpontrentdaohlnela-UUrseoGGvmiCCseewd(gNhdaialelatsxVominaeous1rc,e9oo7ucn3loee)nusgroesafrl(va1aux9tsii5evs9e(,,Maw1Wp9ep7)r4aod)acosclpayhstssttteiohfmieegdauUlsaGitxnhCyge wkwehaesepthatehrenaedaidsribtsuytrubracbnoacmnecpecalniasisospnirfiecosaertniotnnootrinn–doetp.ietAnrdneepnerftefsooerfntwtwehdaesthamerapduthereerltyoe t on 04 Ap glasscopiesofthePSSanddirectIIIaJplatestakenontheBurrell morphologicalratherthanenvironmentalclassification.Ofcourse, ril 2 Schmidt.Thereliabilityofthesetypeswasassessedintwoways. thereisconsiderableoverlapbetweennotingaspiralas‘peculiar’ 01 9 andas‘disturbed’,althoughthe‘peculiar’noteprobablyrefersto First, UGC galaxies were also typed, and comparison with UGC awidervarietyofanomalousmorphologiesthanjustdisturbance. types showed a standard deviation in the class T of ,1.0. Secondly,allgalaxieswereindependentlytypedtwiceandshowed similarlevelofagreement. 2.3.5 Nearby companion For92galaxies,itwasnotpossibletodetermineareliabletype duetheirsmalland/orsaturatedimagesonthePSS.InAbell1367 Finally,whileinspectingthegalaxiesanotewasmadeiftherewas and1656,some41suchgalaxieswithm #15:7wereinspected anearbycompanion(Table4,column9).Althoughgenerallimits p foremissionontheprismplatepairsfortheseclusters.Atotalof of .20 per cent of the size of the galaxy and within ,5 galaxy six galaxies (15 per cent of the sample) were found to have diameterswereapplied,the‘companion’assignmentwasmadeon emission. This is a larger percentage emission detection than for a1–4rankscale(…[nocompanion],C::,C:,C)dependingonthe early-type galaxies (,5 per cent), but much smaller than for degree of certainty and/or strength of the interaction. Smaller galaxiesoftypesSaandlater(,40percent).Weconcludethatthe galaxiesfurtherawaywithnosignsofdistortionaremorelikelyto galaxies with indeterminate type are likely to be predominantly beprojectedcompanions(C::,rank2),whilelargergalaxiescloser q2000RAS,MNRAS317,667–686 672 C. Moss and M. Whittle Table4.CGCGgalaxiessurveyedforHaemission. CGCG UGC R.A.(1950)Dec. r m Type Dis. Cp. v Ref. Haemission Notes p ( (r ) (kms21) Vis. Conc. A Abell262 521-070 1193 1h 39m:5 1358 230 1.24 14.1 Sab … … 5114 1 … … 521-071 1 40.4 136 20 1.12 15.3 SAB: … … 14723 2 … … 521-072 1212 1 41.2 134 9 1.43 14.5 SAb … … 10693 1 … … 521-073 1220 1 41.6 137 26 1.29 13.6 Spec D:: … 5662 1 S D 521-074 1 41.7 134 25 1.28 15.0 S:pec … … 5275 2 S VC 521-076 1221 1 41.7 137 57 1.50 15.0 Sbc … … 11095 2 … … 521-078 1234 1 42.9 134 52 1.01 14.8 Sc/SBc D: … 5653 1 … … 521-080 1238 1 43.4 136 12 0.77 13.5 SA:b … … 4515 1 … … 521-081 1 43.5 134 41 1.02 14.7 S:pec D: … 5417 1 … … 522-003 1 44.0 134 32 1.04 15.2 pec D:: … 4205 2 MS N D 522-004 1248 1 44.3 135 18 0.74 12.9 Sab … … 4756 1 … … o w 522-005 1251 1 44.6 135 47 0.62 15.0 pec D C 4845 2 … … n 522-006 1 44.8 134 46 0.88 15.0 SAbc:pec … … 5557 1 … … lo a 522-007 1257 1 45.2 136 12 0.57 15.0 SA:ab … … 4662 1 … … d e 522-013 1 46.5 134 44 0.78 15.5 S:pec D:: C: 4025 1 … … d 503-030 1 47.7 133 23 1.46 15.3 Spec D … 15086 2 ? ? fro m 522-018 1299 1 47.7 135 7 0.52 15.7 Irr … … 5498 2 … … h 522-020 1302 1 47.8 135 2 0.55 13.3 SBb … (C::) 4047 1 MS C ttp 522-021 1307 1 47.9 135 40 0.27 15.1 S … … 4889 1 MW C s 522-024 1319 1 48.5 135 49 0.17 14.5 SA:pec D:: (C:) 5375 1 W VD ://a 522-025 1 49.1 135 53 0.09 15.6 SAbc: … … 6050 1 … … ca 522-029A 1 49.3 134 55 0.57 (16.4) S D: C … … * de 522-029B 1 49.3 134 55 0.57 (16.4) S … C … … * m ic 522-031 1338 1 49.4 135 33 0.21 15.2 SAb … (C::) 4099 1 … … .o 522-035 1344 1 49.7 136 15 0.20 14.0 SBa … (C::) 3998 1 ? ? u p 522-038 1347 1 49.8 136 22 0.27 13.9 Sc/SBc … [C:] 4099 1 … … .c o 522-041 1349 1 50.0 135 48 0.06 14.3 SABc D:: … 6131 1 W VD m 522-042 1350 1 50.0 136 15 0.20 14.5 SBb … (C::) 5244 1 … … /m 503-044 1 50.1 133 21 1.46 15.7 S … … 11165 2 ? ? nra 522-050 1361 1 50.9 136 20 0.27 15.7 Sc … C: 5244 1 ? ? s 552222--005551 1366 11 5510..49 113366 2322 00..3328 1145..71 SSBAc …… … 54161886 12 …… …… /artic le 522-058 1385 1 52.0 136 41 0.51 14.2 SBa … C: 5529 1 S N -a 522-059 1380 1 52.0 137 5 0.72 15.6 S … … 4600 1 … … b s 522-060 1 52.1 135 11 0.48 15.1 SBab: … … 16200 1 … … tra 522-062 1 52.1 136 41 0.51 15.2 SBb … (C:) 5400 1 … … c 522-063 1387 1 52.2 136 1 0.27 15.4 S-Irr D: (C:) 4502 1 … … t/3 1 522-066 1390 1 52.4 136 3 0.30 15.5 S … … 4368 2 … … 7/3 522-067 1 52.7 137 9 0.78 15.5 Sab:pec: D:: … 14741 2 … … /6 522-069 1398 1 53.0 136 53 0.67 14.9 SAc: … … 5389 1 … … 67 522-071 1400 1 53.2 135 53 0.38 13.8 Sb … C: 4670 1 ? ? /9 6 522-073 1404 1 53.4 136 59 0.74 15.6 SBb … … 4458 1 … … 7 3 522-074 1405 1 53.4 137 12 0.84 15.7 Sc … … 4920 1 … … 7 1 522-075 1 53.4 137 15 0.87 15.7 Irr: … … 5405 1 … … b 522-077 1 53.6 137 5 0.80 15.5 SBb:pec D:: … 5511 2 M N y g 522-078 1411 1 53.7 133 56 1.21 13.9 Sb D:: C: 4748 1 … … u e 522-079 1 53.7 135 21 0.54 15.3 SA:c: … … 5230 2 … … s 522-081 1416 1 53.8 136 39 0.62 14.9 S … … 5484 1 M D t o n 522-082 1 53.9 135 45 0.47 15.3 SA:c:: … … 4818 1 ? ? 0 4 522-086 1437 1 54.8 135 40 0.58 12.6 SAB:c D:: (C:) 4896 1 (S) D * A 522-088 1441 1 54.9 137 7 0.90 15.5 Sb … … 4996 1 … … p 522-090 1 55.1 134 3 1.22 15.7 S:pec ? … 14279 1 … … ril 2 522-094 1456 1 56.0 136 26 0.77 14.0 Sab … … 5057 1 … … 0 1 522-095 1 56.0 137 30 1.15 15.6 SAB:b: … … 14346 1 … … 9 522-096 1459 1 56.1 135 49 0.72 15.4 Sc … … 5466 1 … … 522-097 1460 1 56.1 136 1 0.72 15.0 Sapec D:: … 4874 1 … … 522-100 1474 1 57.2 137 21 1.18 15.0 SB(s)dm … … 4235 1 MW VD 522-102 1493 1 57.9 137 58 1.49 14.0 SB:ab … … 4249 1 W D Abell347 538-034 2 10.9 141 39 1.45 15.0 S D: … 4328 1 ? ? 538-037 1738 2 12.8 142 35 1.36 15.6 Sc … [C:] 5734 1 MW VD 538-038 1743 2 13.1 142 35 1.33 15.7 SBb … [C:] 13708 1 … … 538-040 1780 2 15.9 140 20 1.21 15.6 Irr D:: … 5204 1 … … 538-043 2 16.9 141 3 0.82 15.0 pec D: … 5936 3 S DBL * 538-045 1796 2 17.3 140 34 0.98 15.5 SAB(s)dm … (C:) 6983 1 … … 538-046 2 17.4 141 20 0.69 15.3 SA:b: … … 5920 3 W VD 538-047 2 18.0 141 35 0.58 15.6 SB … … … … 538-048 2 18.2 142 39 0.86 15.3 Spec D: C: 6639 1 MS D 538-050 2 19.1 142 35 0.76 15.7 Sa: ? … … … q2000RAS,MNRAS317,667–686 Hasurvey of Abell clusters 673 Table4 – continued CGCG UGC R.A.(1950)Dec. r m Type Dis. Cp. v Ref. Haemission Notes p ( (r ) (kms21) Vis. Conc. A 538-051 1827 2h 19m:1 1438 190 1.18 15.7 S-Irr … … 5810 2 … … 538-052 1831 2 19.4 142 7 0.51 10.8 Sb … … 527 1 … … 538-053 1832 2 19.4 142 50 0.88 15.4 Sa … … 5913 1 … … 538-054 2 19.7 141 56 0.41 15.7 Sa: … (C::) 6390 3 M VD 538-056 1840 2 20.0 141 9 0.47 14.1 pec: D C 5425 2 … … * 538-058 1842 2 20.2 141 44 0.31 13.8 Sa … (C::) 5400 1 … … 538-059 2 20.8 141 59 0.32 15.7 SBbpec D: (C:) … … 538-061 1855 2 21.4 140 39 0.68 15.1 SBa … … 12849 1 … … 538-062 1858 2 21.6 141 28 0.18 15.7 SB … … 5304 1 ? ? 538-063 2 21.6 141 48 0.17 15.7 Sbc … … 5680 3 M VD 538-066 1866 2 22.0 141 38 0.09 14.9 SBa … (C) 739 1 … … D 539-014 1868 2 22.1 141 52 0.16 14.4 SBa … (C:) 4586 1 … … o w 539-015 2 22.2 141 30 0.12 15.7 S … (C::) … … n 539-023 1887 2 22.9 141 55 0.18 13.9 SAc … (C::) 5548 1 … … lo a 539-024 2 23.6 141 37 0.11 15.0 SBb … … 5723 3 S N d e 539-025 2 23.7 141 28 0.17 15.3 SBpec D: (C:) 4316 3 S N d 539-026 2 23.7 141 48 0.16 15.7 Sa: … (C:) 5548 1 … … fro m 539-027 2 23.8 142 35 0.63 15.7 SB:bc: … … … … h 539-029 2 24.3 141 42 0.20 15.7 S D: (C:) 6740 3 MS VD ttp 539-030 1915 2 24.4 141 45 0.22 14.4 Sb: D:: (C) 5638 3 S D s 539-032 1961 2 26.3 142 2 0.51 15.0 SB:c … … 5631 1 … … ://a 539-036 1988 2 28.1 140 10 1.19 14.7 Sab … … 5814 1 S D ca 539-038 2 28.3 140 2 1.27 15.7 Spec D:: C 5889 3 S N de 539-040 1997 2 29.0 143 14 1.29 15.4 Sb … … 6162 1 … … m 539-041 2001 2 29.2 141 59 0.83 14.6 Sab … (C::) 6989 1 … … ic.o 539-046 2034 2 30.6 140 19 1.32 15.0 Irr … [C::] 579 2 … … u p 539-048 2 30.8 142 28 1.13 15.7 S … … … … .c o 539-052 2058 2 31.8 140 55 1.23 15.6 Sb/SBc … … … … m 539-053 2060 2 31.9 141 9 1.18 14.7 SBab … … 4581 1 … … /m 539-056 2066 2 32.3 140 40 1.36 13.2 Sa … C: 5843 1 … … nra Abell400 s 441155--002221 22337752 22 5511..43 1165 473 00..7777 1155..55 SASB:c …… …… 77690170 11 …W …D /artic le 415-025 2 52.7 15 55 0.48 15.7 S … (C:) 7453 1 W VD -a 415-027 2 53.1 16 8 0.47 15.6 S … … 6760 1 … … b s 415-028 2399 2 53.2 16 0 0.40 15.3 SAB:c … … 8006 1 … … tra 415-030 2405 2 53.3 16 17 0.51 15.1 Sc … … 7709 1 W D c 415-031 2414 2 53.7 14 20 1.28 15.5 Sc … C: 8267 1 … … t/3 1 415-032 2415 2 53.7 15 57 0.29 15.5 SBbc … [C] 6590 1 … … 7 /3 415-035 2419 2 54.0 17 8 1.10 14.8 SBa … … 8090 1 … … /6 415-037 2423 2 54.1 14 47 0.89 15.7 Sc … … 7724 1 … … 67 415-039 2426 2 54.5 15 7 0.61 15.1 SA:b … … 7460 1 … … /9 6 415-042 2 55.1 15 45 0.07 15.7 S:pec D: (C:) 7200 2 … … 7 3 415-048 2444 2 55.8 16 6 0.28 15.2 S … … 6708 1 M D 7 1 415-053 2469 2 57.7 15 31 0.62 15.2 pec: … (C:) 8617 1 … … b 415-058 3 2.0 15 15 1.53 15.7 Sbc: … … 8312 2 (W) VD y g Abell426 u e 540-036 3 2.9 141 33 1.46 15.7 S:c:pec D: … 3610 2 ? ? s 540-039 2534 3 3.3 141 17 1.41 15.7 pec: … … 5306 1 … … t o n 540-042 2538 3 3.8 141 34 1.35 15.6 SBa … … 4046 1 ? ? 0 4 540-043 2544 3 4.2 142 12 1.40 15.0 S … … 5198 1 … … A 540-047 2561 3 6.4 140 48 1.10 15.5 Sb … … 5821 1 … … p 540-049 2567 3 7.0 140 35 1.09 14.3 S-Irr … … 3018 1 M VD ril 2 540-058 3 9.9 142 49 1.12 15.7 Sbpec D:: … 9011 2 … … 0 1 525-009 2604 3 11.5 139 27 1.26 14.8 SBc … … 4520 1 … … 9 540-064 2608 3 11.7 141 51 0.53 14.0 SBb D: C: 7042 1 S N 525-011 2610 3 11.8 139 11 1.41 15.7 Sb … … 5090 1 … … 540-065 2612 3 11.9 141 48 0.49 15.4 Sc … … 6446 1 ? ? 540-067 3 12.0 141 25 0.39 15.3 SA:a: … … 5945 1 M D 540-069 2617 3 12.7 140 43 0.49 14.3 SABc D:: (C:) 4627 1 M C 540-070 2618 3 12.7 141 53 0.46 14.9 Sab … … 5376 1 W D 540-071 3 12.7 142 44 0.93 15.6 SA:a: … … MS N 540-073 2621 3 13.2 141 21 0.25 14.7 Sa … … 4747 1 … … 540-076 2625 3 13.5 139 50 0.96 15.7 S:pec: … … 4252 1 … … 540-078 2626 3 13.7 141 10 0.21 15.7 Sa: … … 6418 2 … … 540-083 2639 3 14.5 141 47 0.30 15.6 Sab … … 4046 1 … … 540-084 2640 3 14.5 143 7 1.12 14.8 SBb … … 6161 1 MS D 540-090 2654 3 15.4 142 7 0.49 14.6 pec: D: C: 5793 1 … … 540-091 2655 3 15.4 143 3 1.07 14.1 SBc … … 6155 1 M C * 540-093 2658 3 15.5 141 18 0.03 14.5 SAb D: (C:) 3124 1 … … q2000RAS,MNRAS317,667–686 674 C. Moss and M. Whittle Table4 – continued CGCG UGC R.A.(1950)Dec. r m Type Dis. Cp. v Ref. Haemission Notes p ( (r ) (kms21) Vis. Conc. A 540-094 2659 3h 15m:6 1408 250 0.57 14.9 Sbc … … 6193 1 S N 540-100 2665 3 16.2 141 27 0.13 15.5 Sc?pec D:: (C:) 7861 1 MW VD 540-103 2669 3 16.5 141 20 0.14 13.0 pec: … … 5264 1 S N 540-106 2672 3 16.8 140 44 0.41 15.7 Sa? … … 4295 1 … … 525-021 3 17.0 139 23 1.24 15.5 SBa: … … … … 540-112A 2688 3 18.0 141 45 0.41 (15.4) pec D: C 3015 1 MS C * 540-112B 2688 3 18.0 141 45 0.41 (16.2) S:pec D C 2882 4 ? ? * 540-114 3 18.3 140 15 0.76 15.6 S:a: … … … … 540-115 3 18.3 141 19 0.35 15.6 Sa: … (C:) 3343 1 ? ? 540-118 2696 3 18.7 142 0 0.57 15.7 S: … … 5454 1 … … 540-121 2700 3 19.6 142 22 0.82 15.5 SB:b … … 6622 1 MW N D 541-003 3 22.2 140 21 1.02 14.9 SAa: ? … M D o w 541-005 2730 3 22.6 140 35 0.98 15.3 Sb … [C:] 3772 2 … … n 541-006 2732 3 22.8 140 37 0.99 15.4 SBb … [C:] 6966 1 … … lo a 541-008 2736 3 23.2 140 20 1.12 14.7 Sab … … 5887 1 … … d e 541-009 2742 3 24.4 140 44 1.14 15.5 SBc … … 4401 1 M C d 541-011 3 25.2 139 59 1.44 15.0 SB:b:pec D: (C:) 4246 1 S N fro m 541-017 2759 3 26.7 141 40 1.35 14.8 pec: D: … 4237 1 S D h Abell569 ttp 234-043 3638 6 59.2 149 30 0.88 14.4 SB:ab … … 5567 1 MW VD s 234-050 3662 7 2.1 150 35 1.34 14.6 SBa: … (C::) 6276 1 … … ://a 234-051 3663 7 2.1 150 50 1.50 14.8 SBa … … 6290 1 … … ca 234-055 7 3.5 148 25 0.29 15.6 S … … 5882 1 … … de 234-056 7 3.8 148 58 0.26 14.8 Spec … C: 6212 2 S N m 234-057 7 4.0 148 29 0.22 15.7 pec … … M N ic.o 234-060 3681 7 4.3 150 45 1.40 14.3 SBb … (C:) 5985 1 … … u p 234-061 7 4.4 149 0 0.23 15.5 SAa: … (C::) 6236 1 W VD .c o 234-062 7 4.4 149 13 0.37 15.1 SB:a: … (C::) 5860 1 … … m 234-065 7 4.7 148 12 0.35 15.6 SB:pec D: (C::) MW VD /m 234-066 3687 7 4.7 150 42 1.37 15.5 pec: D:: (C:) 6164 2 M N nra 234-067 7 5.0 149 4 0.25 15.1 Sa: … … 6258 1 M D s 223344--007619 77 55..43 114498 5349 00..8024 1155..56 SBS:ap:ec D…: (CC:::) 45626926 12 WS DC /artic le 234-079A 3706 7 6.1 147 59 0.50 (15.3) S:pec D C 6115 2 MS N * -a 234-079B 3706 7 6.1 147 59 0.50 (15.7) S:pec D C 6077 2 … … * b s 234-088A 3719 7 7.2 148 35 0.22 (15.4) Sab D:: C 5820 2 … … * tra 234-090 7 7.2 149 5 0.33 15.2 Sbc … … 5956 1 M VD c 234-092 7 7.3 149 58 0.89 15.7 Sa: … … 6296 2 … … t/3 1 234-093 3724 7 7.7 148 19 0.37 14.5 SBb … … 5925 1 MW D 7 /3 234-094 7 7.7 149 10 0.41 15.4 S-Irr … … 6089 2 W VD /6 234-100 3734 7 8.7 147 15 1.06 13.2 SAb … … 955 1 … … 67 234-102 7 9.1 149 5 0.49 15.0 Sb: D:: (C:) … … /9 6 234-103 7 9.1 149 51 0.89 15.2 Sa: … … … … 7 3 234-107 3741 7 10.0 150 20 1.22 15.5 Sc … … 5301 1 … … 7 1 234-114 7 12.5 148 21 0.84 15.6 SAa: … … … … b 235-005 7 15.1 149 18 1.16 15.5 SA … … W VD y g 235-007 7 16.8 149 11 1.32 15.0 Sbc: … … MS VD * u e Abell779 s 180-057 4843 9 9.6 135 7 1.49 14.2 SB … … 1951 1 … … t o n 180-059 9 10.6 133 31 1.10 15.7 S … … 3393 1 … … 0 4 180-060 9 10.6 135 2 1.32 15.4 Sa: … … 7200 1 MW D A 181-006 4894 9 13.7 134 39 0.74 13.9 SBpec D: C: 1681 1 MW N * p 151-048 4908 9 14.2 132 13 1.48 15.7 Sb … … 14737 1 … … ril 2 181-007 9 14.9 134 43 0.67 15.7 SA:a: … … 7002 2 … … 0 1 151-053 9 15.5 132 28 1.23 15.6 SB: … … 8042 1 … … 9 181-012 9 15.5 134 30 0.47 15.5 Sa: … … 7198 1 … … 181-013 4926 9 15.5 134 46 0.66 15.4 Sb: … C: 6365 1 W VD 181-016 4935 9 16.2 134 13 0.21 15.7 SBa … … 6960 1 … … 181-017 9 16.3 133 57 0.09 15.3 S:a: … (C:) 6106 1 … … 181-019 9 16.4 134 31 0.43 15.6 pec D:: C: 13783 2 … … 181-023 4941 9 16.7 133 57 0.03 15.4 S D: C 6106 1 W N 181-026 4947 9 16.9 133 8 0.68 15.3 SB D: … 13790 1 ? ? 181-030 9 17.6 133 17 0.58 15.5 SB:b … … 6449 1 MW N 181-032 4960 9 17.8 135 35 1.29 14.8 SBb … … 7544 1 MW D 181-036 9 19.2 134 8 0.42 15.7 S … (C::) 6025 1 … … 181-037 4988 9 20.2 134 56 0.94 15.7 SABm … … 1575 1 … … 181-042 9 21.9 133 57 0.85 15.6 SBbc: … C:: 12679 2 … … 181-043 5015 9 22.7 134 30 1.06 15.7 SABdm … … 1646 1 … … 181-044 5020 9 23.0 134 52 1.24 15.3 Sc … C 1630 1 … … 181-045 9 24.2 134 39 1.33 15.7 S:b: … … 6465 1 … … q2000RAS,MNRAS317,667–686 Hasurvey of Abell clusters 675 Table4 – continued CGCG UGC R.A.(1950)Dec. r m Type Dis. Cp. v Ref. Haemission Notes p ( (r ) (kms21) Vis. Conc. A Abell1656 159-109 8024 12h 51m:6 1278 250 1.24 14.9 Irr … … 376 2 … … 159-116 8033 12 52.2 129 12 1.20 12.3 Sc … … 2453 1 S N * 160-025 8060 12 54.1 127 15 1.00 14.0 SBa … (C) 6404 1 … … 160-038 8069 12 54.8 129 18 0.97 14.8 SB: D:: (C::) 7472 1 ? ? 160-043 8071 12 55.1 128 28 0.45 15.4 S … C 7069 1 … … 160-050 8076 12 55.4 129 55 1.40 15.2 SAB:c … … 5304 1 MW VD 160-055 8082 12 55.7 128 31 0.37 14.2 SB:ab D:: … 7227 1 S N * 160-058 12 55.8 128 59 0.66 15.5 S … … 7609 1 M D 160-062A 12 55.9 129 24 0.97 (15.8) pec D C 7837 2 … … * 160-062B 12 55.9 129 24 0.97 (15.8) pec D C … … * D 160-064 12 56.1 127 31 0.64 15.4 pec D: … 7368 1 S N o w 160-067 12 56.2 127 26 0.70 15.4 pec D:: … 7664 1 S N n 160-073 8096 12 56.5 128 6 0.20 14.9 S … … 7526 1 … … lo a 160-075 12 56.6 128 23 0.18 15.5 pec D: [C] 9386 1 M N d e 160-099 12 57.2 128 54 0.53 15.6 Sa: … … 5327 1 MS N d 160-110 8108 12 57.6 127 10 0.88 14.7 S … … 5898 1 … … fro m 160-113A 12 57.7 128 8 0.11 (16.0) pec … [C] 5128 2 MW N * h 160-127 12 58.1 127 55 0.30 15.4 pec D:: … 7476 1 S N ttp 160-130 12 58.2 128 20 0.16 15.1 pec: D:: … 7633 1 S N s 160-132 8118 12 58.2 129 17 0.85 14.6 S … … 7275 1 … … ://a 160-139 12 58.4 128 26 0.23 14.6 SB:ab … … 5807 1 … … ca 160-140 8128 12 58.5 128 4 0.25 13.7 S D: C 7973 1 … … de 160-147 8134 12 59.0 128 8 0.30 13.7 SABa … … 5475 1 … … m 160-148A 8135 12 59.0 129 35 1.12 (15.0) Spec D C 7056 1 S VC * ic.o 160-148B 8135 12 59.0 129 35 1.12 (15.0) Spec D C 7153 1 … … * u p 160-150 12 59.1 128 57 0.64 15.3 Spec D:: … 8909 1 M D .c o 160-154 8140 12 59.4 129 19 0.94 14.8 Sab … … 7099 1 M D m 160-159 12 59.7 129 31 1.11 14.9 Sa: … … 5823 1 … … /m 160-160 12 59.8 128 29 0.47 15.5 pec … [C:] 8311 1 S N nra 160-164A 13 0.2 128 22 0.51 (16.3) SB: … C 7476 2 … … * s 116600--117723 88116601 1133 01..90 112286 1479 01..6333 1155..05 SS: …D: (…C:) 66069727 11 …… …… /artic le 160-176A 8167 13 1.5 128 28 0.75 (13.5) Sab … C 7111 1 … … * -a 160-178 13 2.0 126 56 1.35 15.3 Sa: … … 10814 1 … … b s 160-179 13 2.0 127 34 0.99 15.5 S:pec D: … 5523 1 MS N tra 160-180 13 2.0 129 5 1.06 15.3 pec D: … 8050 1 S N c 160-186 8185 13 3.3 128 0 1.07 13.5 Sc … … 2533 1 MW VD t/3 1 160-189A 8194 13 3.9 129 20 1.45 (14.0) S D: C 7135 2 … … * 7 /3 160-191 13 4.2 129 6 1.39 15.0 pec D: … 4837 1 S N * /6 6 7 References:1.Huchraetal.(1995).2.NasaExtragalacticDatabase.3.Mossetal.(1988).4.Straussetal.(1992). /9 Notesonindividualobjects: 6 7 CGCG522-029AandB:southandnorthcomponentsrespectivelyofdoublegalaxysystem. 37 CGCG522-086:Emissionislocated,39arcsecwestofanorth–southlinethroughthegalaxycentre. 1 b CGCG538-043:Emissionisdouble. y CGCG538-056:Ringgalaxywithcompanion39arcsectoeast. gu CGCG540-091:Possibleadditionalemission,8arcsecwestofanorth–southlinethroughthegalaxycentre. es CGCG540-112AandB:northandsouthcomponentsrespectivelyofdoublesystem. t o CGCG234-079AandB:southandnorthcomponentsrespectivelyofdoublesystem.Interactingpair. n 0 CGCG234-088A:southcomponentofdoublegalaxysystem. 4 A CGCG235-007:Emissionhastwocentres. p CCGGCCGG118519--010166::REminigssgioalnaxhyaswmituhltciopmlepcaonmiopnon9e5natrsc.sectonorth-west. ril 20 CGCG160-055:Emissionisdouble. 19 CGCG160-062AandB:northandsouthcomponentsrespectivelyofdoublesystem. CGCG160-113A:westcomponentofdoublegalaxysystem. CGCG160-148AandB:north-eastandsouth-westcomponentsrespectivelyofdoublesystem.Interactingpair. CGCG160-164A:eastcomponentofdoublegalaxysystem. CGCG160-176A:westcomponentofdoublegalaxysystem. CGCG160-189A:eastcomponentofdoublegalaxysystem. CGCG160-191:Emissionispossiblydouble. ExplanationsofcolumnsinTable4. Column1.CGCGnumber(Zwickyetal.1960–1968).ThenumberingofCGCGgalaxiesinfield160(Abell1656),whichhasasubfieldcoveringthe densecentralregionofthecluster,followsthatofthelistingoftheCGCGintheSIMBADdatabase.Theenumerationisinstrictorderofincreasing RightAscension,withgalaxiesoflowerdeclinationpreceedingincasesofidenticalRightAscension. Column2.UGCnumber(Nilson1973). Columns3and4.RightAscensionandDeclination(1950.0)ofthegalaxycentretakenfromtheCGCG. Column5.RadialdistanceinAbellradii(Abell1958)ofthegalaxywithrespecttotheclustercentre.Positionsoftheclustercentresandvaluesofthe AbellradiiforthevariousclustersarelistedinTable1. q2000RAS,MNRAS317,667–686 676 C. Moss and M. Whittle Table4 – continued Column6.CGCGphotographicmagnitude.Fordoublegalaxies,magnitudeestimatesforindividualcomponentsobtainedbyeyefromPSSaregivenin parentheses. Column7.GalaxytypetakenfromUGCorestimatedfromthePSS. Column8.Codeindicatingthatthegalaxyappearsdisturbed,onafour-rankscale(…[nodisturbance],D::,D:,D). Column9.Codeindicatingthatthegalaxyhasapossiblenearbycompanion,onafour-rankscale(…[nocompanion],C::,C:,C).Squarebrackets indicatethatthecompanionislikelytobeachancesuperposition,orhasnegligibletidalinteractionwiththegalaxy;parenthesesindicatethatthe probabilityofthecompanionbeingachancesuperposition,P.0:05(seeSection2.3.5). Columns10and11.Heliocentricvelocityandreference. Column12.AvisibilityparameterdescribinghowreadilytheHaemissionisseenontheplatesaccordingtoafive-pointscale(Sstrong,MSmedium- strong,Mmedium,MWmedium-weak,Wweak).A‘?’inthiscolumnandcolumn13indicatesthatthegalaxywasnotsatisfactorilysurveyedfor emissionforavarietyofreasons:overlapbyanadjacentstellarorgalaxyspectrum(CGCGnos.522-035,522-050,522-071,522-082,538-062,540- 115,540-112B,540-065,540-042);overlapbyaghostimage(CGCGno.181-026);platedefect(CGCGno.160-038);galaxyliesoutsidetheoverlap regionoftheplatepair(CGCGnos.503-030,503-044,538-034,540-036). Column13.Aconcentrationparameterdescribingthespatialdistributionoftheemissionandcontrastwiththeunderlyingcontinuum,onafive-point D scale(VDverydiffuse,Ddiffuse,Nnormal,Cconcentrated,VCveryconcentrated). o Column14.Notes.Anasteriskinthiscolumnindicatesthatanoteonthisgalaxyappearsbelowthetable. w n lo a d by with tidal features are likely to be genuine companions (C, cent have jDvj.1500kms21: The final selected sample of e d rank4). galaxies with ‘real’ companions comprises 45galaxies, of which fro A principal difficulty in defining a robust parameter for the some 22 have known jDvj: Thus the contamination of the final m h presence/absenceofnearbycompaniongalaxiesistheuncertainty samplebynon-tidallyinteractingpairsisexpectedtobe*11per ttp rfeagraarpdainrtg. Tprhoijsecistioanpeafrfteiccutsla—r praopbplaermenitnlytchleoscerogwadlaexdiefsiemldayofbae cent. s://ac a cluster. To help overcome this problem, we use two screening d 3 Ha DETECTION AND GALAXY e criteria: one using velocity and one using local galaxy surface m PROPERTIES ic density. .o u First, if velocities were available for both the galaxy and its Before investigating the relation between star formation and p .c companion, and the absolute value of the velocity difference environment, it is important first to establish the dependence of o m jDvj.1500kms21; then it is assumed either that the projected star formation onintrinsicgalaxy properties.This topic has been /m companion is a chance superposition or, due to the high velocity discussedinPapersIIandIII.Makingfulluseofthefinalgalaxy nra difference,thereisnegligibletidalinteraction.Ineithercase,these survey sample, we review here in rather more detail the s/a galaxieswerenolongerconsideredtohave‘real’companions,and dependence of detected Ha emission on a variety of galaxy rtic weregroupedwith‘isolated’galaxiesforthesubsequentanalysis. propertiesandonthepresenceorabsenceofanearbycompanion. le -a These galaxies have their companion parameters listed in square WeshowthatthedetectedHaemissioncanbewellunderstoodas b s brackets in Table 4. For Abell 1367 (Paper III, table 2), galaxies either normalspiraldiscemission,orascircumnuclearstarbursts tra c CGCG nos.97–125and97–133A are alsointhis category. triggeredeitherbytidalforcesonthegalaxyorbyabar.Inatleast t/3 Intheabsenceofthisvelocitycriterion,anattemptwasmadeto some cases the tidal forces are due to a companion galaxy. The 17 estimatethelocalgalaxysurfacedensity.Withinan18-arcminbox relation of the detected emission (whether disc emission or /3/6 centred on the main galaxy, a count was made of the number of circumnuclear starburst)to thecluster environmentof thegalaxy 67 galaxies of a similar or greater size to the projected companion. will discussed inSection 4below. /96 7 For those cases in which the projected companion was of 3 7 relatively large size such that very few, or no similar or larger 3.1 Apparentandabsolutemagnitudes 1 b galaxies were counted in the 18-arcmin box, the count was y g repeatedfora1-degsquarebox.Thecountswereusedtoestimate In Paper III we showed that for galaxies in Abell 1367 the Ha ue s themeansurfacegalaxydensityintheregion,andtheprobability, detection efficiency was approximately independent of apparent t o P, was computed that the projected companion was a chance magnitude down to the CGCG limit, mp(cid:136)15:7: For our new n 0 superposition (assuming that the galaxies were distributed ran- largersamplefromalleightclusters(typesSaandlater,omitting 4 A domly across the field). For P.0:05; the sample galaxy was irregularsorpeculiars)weconfirmthisearlierresult.Kolmogorov– p omitted from the companion ranking, which is given in paren- Smirnov(K–S) testswhichcomparethecumulativedistributions ril 2 0 theses in Table 4. For Abell 1367 (Paper III, table 2), galaxies of apparent magnitude of non-ELGs with either compact ELGs, 1 9 which have been similarly omitted from the companion ranking diffuse ELGs, or all ELGs, all show no significant differences areCGCGnos.97-044,97-066,97-068,97-120A,127-036,127- (significancelevels0.27,0.71and 0.24respectively). 046,127-085and 127-090. Is the same true for absolute magnitude? First, we evaluated Lastly,forP#0:05;theprojectedcompanionwasacceptedas correctedmagnitudes,B0 followingstandardmethods:converting T a ‘real’ companion and assigned a rank according to the CGCG magnitudes, m , first to the B system following Paturel, p T companionassignment given inTable4. Bottinelli&Gouguenheim(1994),andthencorrectingforgalactic The above procedure which selects galaxies likely to have and internal absorption following Sandage & Tammann (1987). tidallyinteractingcompanionsisnotquiteideal.Inparticular,the Finally, absolute magnitudes, M0; were obtained using cluster B presence of subclustering undermines the assumption of random mean redshifts. Again, K–S tests which compare the cumulative galaxy distribution around the main galaxy. A cleaner method distributions of absolute magnitude for non-ELGs with either would require velocity data for many fainter galaxies, which are compactELGs,diffuseELGs,orallELGs,allshownosignificant not yet available. For the present sample, there are 36 galaxy– differences(significancelevels 0.37,0.58 and0.60 respectively). companion pairswith P#0:05and knownjDvj;of these 22per Because Hadetection depends on Hubble type (though only q2000RAS,MNRAS317,667–686