Weak lensing study of dark matter filaments and ap

arXiv:astro-ph/0406541v22Jun2005Astronomy&Astrophysicsmanuscriptno.1523February2,2008(DOI:willbeinsertedbyhandlater)WeaklensingstudyofdarkmatterfilamentsandapplicationtothebinaryclusterA222andA223⋆J.P.Dietrich1,P.Schneider1,D.Clowe1,E.Romano-D´ıaz2,andJ.Kerp31Institutf¨urAstrophysikundExtraterrestrischeForschung,Universit¨atBonn,AufdemH¨ugel71,53121Bonn,Germany2KapteynAstronomicalInstitute,UniversityofGroningen,P.O.Box800,9700AVGroningen,TheNetherlands3RadioastronomischesInstitut,Universit¨atBonn,AufdemH¨ugel71,53121Bonn,GermanyReceived24.06.2004/Accepted19.05.2005Abstract.WepresentaweaklensinganalysisofthedoubleclustersystemAbell222andAbell223.Thelensingreconstructionshowsevidenceforapossibledarkmatterfilamentconnectingbothclusters.ThecaseforafilamentaryconnectionbetweenA222/223issupportedbyananalysisofthegalaxydensityandX-rayemissionbetweentheclusters.UsingtheresultsofN-bodysimulations,wetrytodevelopacriterionthatseparatesthissystemintoclusterandfilamentregions.Theaimistofindatechniquethatallowsthequantificationofthesignificanceof(weaklensing)filamentcandidatesinclosepairsofclusters.Whilethismostlyfails,theaperturequadrupolestatistics(Schneider&Bartelmann1997)showssomepromiseinthisarea.TheclustermassesdeterminedfromweaklensinginthissystemareconsiderablylowerthanthosepreviouslydeterminedfromspectroscopicandX-rayobservations(Dietrichetal.2002;Proustetal.2000;Davidetal.1999).Additionally,wereporttheserendipitousweaklensingdetectionofapreviouslyunknownclusterinthefieldofthisdoubleclustersystem.Keywords.Gravitationallensing–Galaxies:clusters:general–Galaxies:clusters:individual:A222–Galaxies:clusters:individual:A223–large-scalestructureofUniverse1.ThecosmicwebThetheoryofcosmicstructureformationpredictsthroughN-bodysimulationsthatmatterintheuniverseshouldbecon-centratedalongsheetsandfilamentsandthatclustersofgalax-iesformwheretheseintersect(e.g.Klypin&Shandarin1983;Davisetal.1985;Bertschinger&Gelb1991;Bondetal.1996;Kauffmannetal.1999).Thisfilamentarystructure,of-tenalsodubbed“cosmicweb”,hasbeenseeningalaxyred-shiftsurveys(e.g.Joeveeretal.1978;deLapparentetal.1986;Giovanellietal.1986;Geller&Huchra1989;Vogeleyetal.1994;Shectmanetal.1996)andmorerecentlybyBaughetal.(2004)andDoroshkevichetal.(2004)inthe2dFandSDSSsurveys,andathigherredshiftbyM¨oller&Fynbo(2001).ObservationalevidenceforthecosmicwebisrecentlyalsocomingfromX-rayobservations.E.g.anX-rayfilamentbe-tweentwogalaxyclusterwasobservedbyTittley&Henriksen(2001).Nicastro(2003)andZappacostaetal.(2002)reportedpossibledetectionsofwarm-hotintergalacticmediumfila-ments.Becauseofthegreatlyvaryingmass-to-light(M/L)ratiosbetweenrichclustersandgroupsofgalaxies(Tully&ShayaSendoffprintrequeststo:J.P.Dietrich,e-mail:[e-mail]⋆BasedonobservationsmadeatESO/LaSillaunderprogramNos.064.L-0248,064.O-0248,66.A-0165,68.A-0269.1999)itisproblematictoconvertthemeasuredgalaxyden-sitiestomassdensitieswithoutmakingfurtherassumptions.DynamicalandX-raymeasurementsofthefilamentmasswillnotyieldaccuratevalues,asfilamentarystructuresareprobablynotvirialized.Weakgravitationallensing,whichisbasedonthemeasurementofshapeandorientationparametersoffaintbackgroundgalaxies(FBG),isamodel-independentmethodtodeterminethesurfacemassdensityofclustersandfila-ments.DuetothefiniteellipticitiesoftheunlensedFBGev-eryweaklensingmassreconstructionisunfortunatelyanin-herentlynoisyprocess,andtheexpectedsurfacemassdensityofatypicalfilamentistoolowtobedetectedwithcurrenttele-scopes(Jainetal.2000).Cosmicwebtheoryalsopredictsthatthesurfacemassden-sityofafilamentincreasestowardsacluster(Bondetal.1996).Filamentsconnectingneighboringclustersshouldhavesurfacemassdensitieshighenoughtobedetectablewithweaklensing(Pogosyanetal.1998).Suchfilamentsmayhavebeendetectedinseveralrecentweaklensingstudies.Kaiseretal.(1998)foundapossiblefilamentbetweentwoofthethreeclusterinthez=0.42superclusterMS0302+17,butthedetectionremainssomewhatuncertainbecauseofapos-sibleforegroundstructureoverlappingthefilamentandpossi-bleedgeeffectsduetothegapbetweentwoofthecamerachipslyingonthefilament.Also,Gavazzietal.(2004)couldrecentlynotconfirmthepresenceofafilamentinthissystem.Grayetal.2J.P.Dietrichetal.:WeaklensingstudyofdarkmatterfilamentsandapplicationtothebinaryclusterA222andA223(2002,G02)claimtohavefoundafilamentextendingbetweentwoofthethreeclustersoftheAbell901/902supercluster,butthesignificanceofthisdetectionislowandsubjecttopossibleedgeeffects,asagainthefilamentisonthegapbetweentwochipsofthecamera.Cloweetal.(1998)reportedthedetectionofafilamentextendingfromahigh-redshift(z=0.809)cluster.Duetothesmallsizeoftheimageitisunknownwhetherthisfilamentextendstoanearbycluster.1.1.TheA222/223systemA222/223aretwoAbellclustersatz≈0.21separatedby∼14′onthesky,or∼2800h−170kpc,belongingtotheButcheretal.(1983)photometricsample.BothclustersarerichhavingAbellrichnessclass3(Abell1958).TheBautz-MorgantypesofA222andA223areII-IIIandIII,respectively.Whiletheseareopticallyselectedclusters,theyhavebeenobservedbyROSAT(Wang&Ulmer1997;Davidetal.1999)andarecon-firmedtobemassiveclusters.A223showscl