Clusters and Superclusters in the Sloan Digital Sk

arXiv:astro-ph/0212312v113Dec2002Astronomy&Astrophysicsmanuscriptno.einastoFebruary2,2008(DOI:willbeinsertedbyhandlater)ClustersandSuperclustersintheSloanDigitalSkySurveyJ.Einasto1,G.H¨utsi1,M.Einasto1,E.Saar1,D.L.Tucker2,V.M¨uller3,P.Hein¨am¨aki1,4,S.S.Allam5,21TartuObservatory,EE-61602T˜oravere,Estonia2FermiNationalAcceleratorLaboratory,MS127,POBox500,Batavia,IL60510,USA3AstrophysicalInstitutePotsdam,AnderSternwarte16,D-14482Potsdam,Germany4TuorlaObservatory,V¨ais¨al¨antie20,Piikki¨o,Finland5NationalResearchInstituteforAstronomy&Geophysics,HelwanObservatory,Cairo,EgyptReceived09.12.2002/Accepted...Abstract.Weapplythe2-dimensionalhigh-resolutiondensityfieldofgalaxiesoftheEarlyDataReleaseoftheSloanDigitalSkySurveywithasmoothinglengths0.8h−1Mpctoextractclustersandgroupsofgalaxies,andalow-resolutionfieldwithsmoothinglengths10h−1Mpctoextractsuperclustersofgalaxies.WeinvestigatepropertiesofdensityfieldclustersandsuperclustersandcomparepropertiesoftheseclustersandsuperclusterswithAbellclusters,andsuperclustersfoundonthebasisofAbellclusters.Wefoundthatclustersinhigh-densityenvironmenthavealuminosityafactorof∼5higherthaninlow-densityenvironment.ThereexistsalargeanisotropybetweentheSDSSNorthernandSouthernsampleinthepropertiesofclustersandsuperclusters:mostluminousclustersandsuperclustersintheNorthernsampleareafactorof2moreluminousthantherespectivesystemsintheSouthernsample.Keywords.cosmology:observations–cosmology:large-scalestructureoftheUniverse;clustersofgalaxies1.IntroductionClustersandgroupsofgalaxiesarethebasicbuildingblocksoftheUniverseoncosmologicalscales.Thefirstcataloguesofclustersofgalaxies(Abell1958,Zwickyetal.1961–68)wereconstructedbyvisualinspectionofthePalomarObservatorySkySurveyplates.Morerecentcataloguesofclusters,aswellascataloguesofgroupsofgalaxies,havebeenderivedusingcataloguesofgalaxies(Huchra,Davis,Latham,&Tonry(1983),Daltonetal.(1997)).Movingupthehierarchyoflarge-scalestructure,galaxyclustercataloguesthemselveshavebeenusedtodefinestilllargersystemssuchassuperclustersofgalaxies(Einastoetal.1994,1997,2001,hereafterE94,E97andE01).ThegoalofthepresentpaperistomaptheUniverseuptoredshiftz=0.2andtofindgalaxyclustersandsuperclustersusingthedensityfieldmethod.Theappli-cationofthedensityfieldisnotnew.Inthepioneer-ingstudybyDavis&Huchra(1982)thedensityfieldwasusedtocalculatethegravitationalfieldofthenearbyUniverse.Gott,Melott&Dickinson(1986)usedthedensityfieldtoinvestigatetopologicalpropertiesoftheUniverse.Bertschingeretal.(1990)calculatedthepoten-tial,velocity,anddensityfieldsfromredshift-distancedata.Saundersetal.(1991)appliedthedensityfieldtoSendoffprintrequeststo:J.EinastomaptheUniverse,tofindsuperclustersandvoids,andcalculatedmomentsofthedensityfield.Marinonietal.(1999)reconstructedrealspacelocaldensityfield.Inthesestudiesnearbyopticalorinfraredgalaxysampleswereused.Morerecently,Hoyleetal.(2002)usedsmoothed2-dimensionaldensityfieldsfromvolumelimitedsubsam-plesofSDSSEDRgalaxiestodiscussthe2-dimensionalgeometryofthelarge-scalematterdistributionincom-parisonwithΛCDMsimulations,andShethetal.(2002)advertisedanewmethodofevaluatingisodensitycon-toursofsmoothed3-dimensionaldensityfieldsfromsim-ulationsforcharacterizingtopologicalpropertiesofthesupercluster-voidnetwork.WecalculatethedensityfieldoftheSloanDigitalSkySurveyEarlyDataRelease(SDSSEDR)byStoughtonetal.(2002),asdescribedbyH¨utsietal.(2002,hereafterPaperI),tofindclustersandsuperclustersofgalaxies,andtoinvestigatetheirproperties.ClustersofgalaxiesfromtheSDSSwereextractedpreviouslybyGotoetal.(2002)usingthecutandenhancemethod;Kimetal.(2002)com-paredvariousclusterdetectionalgorithmsbasedonSDSSdata.Inthispaperwedefineclustersasenhancementsofthedensityfieldandusevarioussmoothinglengthstoseparatesystemsofgalaxiesofdifferentsizeandlu-minosity.Weuseahigh-resolutiondensityfieldtofindclustersandgroupsofgalaxies.Forsimplicity,weusetheterm“DF-clusters”forbothgroupsandclustersfound2J.Einastoetal.:SDSSclustersandsuperclustersTable1.DataonSDSSEDRgalaxies,clustersandsuperclustersSampleDECRAΔRAα1M∗1α2M∗2NgalNclNACONsclSDSS.N0◦190.25◦90.5◦−1.06−21.55−1.22−20.801520928682224SDSS.S0◦23.25◦65.5◦−1.06−21.40−1.10−20.711188222871616inthehigh-resolutiondensityfieldofgalaxies.Similarly,weusealow-resolutiondensityfieldtoconstructacat-alogueofsuperclustersofgalaxies,anddenotethemas“DF-superclusters”.DF-clustersandsuperclustersarede-finedasenhancementsofthedensityfield,DF-clustersinafixedvolume(±2.5h−1Mpcfromthecentre),andDF-superclustersashigh-densityregionssurroundedbyafixedisodensitycontour.IndeterminingDF-clustersandsuperclusterswetakeintoaccountknownselectioneffects.WeshallinvestigatesomepropertiesofDF-clustersandsuperclusters,andstudytheseclustersandsuperclustersastracersofthestructureofthelocalUniverse.ThisstudyisofexploratorycharactertofindthepotentialofSDSSdatatoanalysethestructureoftheUniversebothonsmallandlargescales.InthisstageweusethefactthatSDSSEDRcoversonlyrelativelythinslices;thuswecalculatethedensityfieldin2dimensionsonly.Asmoredatawillbemadeavailableweplantouseafull3-dimensionaldatasettodetectclus