A New Large Catalog of Groups of Galaxies in the Southern Galactic Hemisphere

We present a large catalog of $N_G \approx 200$ loose groups of galaxies selected from the Perseus-Pisces redshift Survey.

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991 voN 11 1v4111179/hp-ortsa:viXraANEWLARGECATALOGOFGROUPSOFGALAXIES

INTHESOUTHERNGALACTICHEMISPHERE

ROBERTOTRASARTI–BATTISTONI

TheoretischePhysik,Ludwig-Maximilians-Universit¨at,

Theresienstr.37,D-80333M¨unchen,Germanyemail:roberto@stat.physik.uni-muenchen.de

WepresentalargecatalogofNG≈200loosegroupsofgalaxiesselectedfromthePerseus–PiscesredshiftSurvey(PPS)intheSouthernGalacticHemisphere.

Galaxygroupscanberegardedassystemsintermediatebetweengalaxiesandgalaxyclusters.Theyprovideconstraintsoncosmologicalmodelsthroughtwodi erentroutes:asgalaxysystems,throughtheirinternalproperties(ve-locitydispersionσv,radiusR,etc.);asLSStracers,throughtheir“external”properties(abundance,clustering,fractionofgroupedgalaxies,etc.).Loosegroupsofgalaxiesaremoderatedensityenhancements(δn/n～10-100)con-sistingoffewmembers(Nmem～3-30,typically5).Bytheirverynature,theyarethen(1)verynumerous,thussuitableforstatisticalstudies,but(2)somehowelusivetode ne,thusrequiringcareintheidenti cationprocedure.

Severallargecatalogsofloosegroupsarenowadayavailablefromthemlim=15.5redshiftsurveysCfA2SliceandCfA2NorthintheNorthernGalac-ticHemisphere(Ramellaetal.1989;Ramellaetal.1997)butnoneofthemcoverstheregionofthePerseus–PiscesSurvey(PPS)( 1h.50≤α≤+3h.00,0o≤δ≤40o,mlim=15.5forthesamplePPS2consideredhere.)Therefore,ourtargetistobuildanewgroupsamplewhichisatthesametime:(1)large,internallyhomogeneous,andindependentfromothersamples(2)objectivelyde ned,andashomogeneousaspossibletotheothersamples.Groupsarethenidenti edwiththeredshift–spaceadaptiveFriends–Of–Friends(FOF)al-gorithmofHuchra&Geller(1982).ThetwolinksDLandVLarenormalizedbyD0=0.231h 1MpcandV0=350kms 1atcz0=1000kms 1,andthenscaledwithcztocompensateforthee ectofmlim.

Thegalaxyluminosityfunction(LF)appropriateforPPS(α=3 1.15±0.15,M = 19.3±0.1,Trasarti–Battistoni1996;φ =0.02h3Mpc ,Marzkeetal.1994),andtheadoptedD0,togetheryieldadensitythresholdδn/n≈180.Thisisratherdi erentfromthedesiredδn/n≈80appropriatefortheothersamples,mostlyduetotheirdi erentLFnormalizationφ since(1+

δn/n)∝φ 1D 3

0.Wethenconsiderseveralotherlinknormalizations.(Thee ectsongroupclusteringarediscussedinTrasarti–Battistonietal.1997.)

showsthattheinternal(median)propertiesofFOFgroupsarevery

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