PUB IRMA LILLE Vol No IX

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PUB. IRMA, LILLE 2009 Vol. 69, No IX Filaments in observed and mock galaxy catalogues R. S. Stoica? Universite Lille 1 Laboratoire Paul Painleve 59655 Villeneuve d'Ascq Cedex France V. J. Martınez† Observatori Astronomic, Universitat de Valencia Apartat de correus 22085 46075 Valencia, Spain E. Saar‡ Tartu Observatoorium, To˜ravere 61602 Estonia Resume The main feature of the spatial large-scale galaxy distribution is an intricate network of galaxy filaments. The present paper compares the filaments in the real data and in the numerical models, to see if our best models reproduce statistically the filamentary network of galaxies. Resume Le reseau filamentaire est la caracteristiques principale de la distribu- tion spatiale a large echelle des galaxies. Ce papier compare la structure filamentaire dans des donnees reelles et synthetiques afin de verifier si les meilleurs modeles sont capables de reproduire des reseaux ayant les memes caracteristiques statistiques que les observations. Keywords: marked point processes, statistical inference, cosmology observa- tions, large-scale structure of the Universe. 1 Introduction The large-scale structure of the Universe traced by the three-dimensional distri- bution of galaxies shows intriguing patterns: filamentary structures connecting

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PUB.IRMoA,LILLE2009Vol.69,NIXFilamentsinobservedandmockgalaxycataloguesR.S.StoicaUniversite´Lille1LaboratoirePaulPainleve´59655Villeneuved’AscqCedexFranceV.J.Martı´nezObservatoriAstrono`mic,UniversitatdeVale`nciaApartatdecorreus2208546075Vale`ncia,SpainE.SaarTartuObservatoorium,To˜ravere61602EstoniaRe´sume´Themainfeatureofthespatiallarge-scalegalaxydistributionisanintricatenetworkofgalaxyfilaments.Thepresentpapercomparesthefilamentsintherealdataandinthenumericalmodels,toseeifourbestmodelsreproducestatisticallythefilamentarynetworkofgalaxies.R´esume´Lere´seaufilamentaireestlacaracte´ristiquesprincipaledeladistribu-tionspatialea`largee´chelledesgalaxies.Cepapiercomparelastructurefilamentairedansdesdonne´esre´ellesetsynthe´tiquesafindeve´rifiersilesmeilleursmode`lessontcapablesdereproduiredesre´seauxayantlesmeˆmescaracte´ristiquesstatistiquesquelesobservations.Keywords:markedpointprocesses,statisticalinference,cosmologyobserva-tions,large-scalestructureoftheUniverse.1IntroductionThelarge-scalestructureoftheUniversetracedbythethree-dimensionaldistri-butionofgalaxiesshowsintriguingpatterns:filamentarystructuresconnecting
XI3Figure1:Galaxymapfortwo2dFGRSslicesofthicknessof2.6.Thefilamen-tarynetworkofgalaxiesisclearlyseen.inhugeclusterssurroundnearlyemptyregions,theso-calledvoids.Asanex-ample,weshowhereamapfromthe2dFGalaxyRedshiftSurvey(2dFGRS,[8]).Inordertobettershowthefilamentarynetwork,Fig.1showsthepositionsofgalaxiesintwo2.6thickslicesfromtwospatialregionsthatthe2dFGRScovered.Thedistancesaregiveninredshiftsz;approximately,thephysicaldistanceD3000h1zMpc1.Filamentsvisuallydominatethegalaxymaps.Realthree-dimensionalfila-mentshavebeenextractedfromthegalaxydistributionasaresultofspecialobservationalprojects([22]),orbysearchingforfilamentsinthe2dFGRScat-alogue([23]).Thesefilamentshavebeensearchedforbetweengalaxyclusters,determiningthedensitydistributionanddecidingifitisfilamentary,individu-allyforeveryfilament.FilamentsarealsosuspectedtohidehalfofthewarmgasintheUniverse;anexampleofadiscoveryofsuchgasisthepaperby[38].However,therearestillnostandardmethodstodescribetheobservedfila-mentarystructure,butmuchworkisbeingdoneinthisdirection.Theusualsecond-ordersummarystatisticsasthetwo-pointcorrelationfunctionorthepowerspectrumdonotprovidemorphologicalinformation.Minkowskifunc-tionals,minimalspanningtree(MST),percolationandshapefindershavebeenintroducedforthispurpose(forareviewsee[18]).Theminimalspanningtreewasintroducedincosmologyby[4].Itisauniquegraphthatconnectsallpointsoftheprocesswithoutclosedloops,butitdescribesmainlythelocalnearest-neighbourdistributionanddoesnotgiveustheglobalandlarge-scalepropertiesofthefilamentarynetwork.Arecentdevelopmentoftheseideasispresentedby[6].Heappliesaminimalspanningtreeonagrid,andworksclosetothepercolationregime–thisallowstostudytheglobalstructureofthegalaxydistribution.Wenotethatusingagridintroduces1HereandbelowhisthedimensionlessHubbleconstant,H=h100km/sec/Mpc.