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1、A&Amanuscriptno.(willbeinsertedbyhandlater)ASTRONOMYANDYourthesauruscodesare:ASTROPHYSICS12.03.4;12.12.1;11.06.15.2.2008TidaltorquesandtheclustersofgalaxiesevolutionA.DelPopolo1,2,andM.Gambera1,31IstitutodiAstronomiadell’Universit`adiCatania,VialeA.Doria,6-I95125Catania
2、,ITALY2Facolt`adiIngegeneria,Universit`aStatalediBergamo,PiazzaRosate,2-I24129Bergamo,ITALY3OsservatorioAstrofisicodiCataniaandCNR-GNA,VialeA.Doria,6-I95125Catania,ITALYAbstract.Westudytheeffectoftidaltorquesonthecollapseofdensitypeaksthroughtheequationsofmotionofashellof
3、barionicmatterfallingintothecentralregionsofaclusterofgalaxies.Wecalculatethetimeofcollapseoftheperturbationtakingintoaccountthegravitationalinteractionofthequadrupolemomentofthesystemwiththetidalfieldofthematteroftheneighbouringproto-clusters.Weshowthatwithinhigh-densit
4、yenvironments,suchasrichclustersofgalaxies,tidaltorquesslowdownthearXiv:astro-ph/9802214v116Feb1998collapseoflow-νpeaksproducinganobservablevariationinthetimeofcollapseoftheshelland,asaconsequence,areductioninthemassboundtothecollapsedperturbation.Moreover,thedelayofthe
5、collapseproducesatendencyforlessdenseregionstoaccretelessmass,withrespecttoaclassicalsphericalmodel,inducingabiasingofover-denseregionstowardhighermass.FinallywecalculatethebiascoefficientusingaselectionfunctionproperlydefinedshowingthatforaStandardColdDarkMatter(SCDM)mode
6、lthisbiascanaccountforasubstantialpartofthetotalbiasrequiredbyobservationsonclusterscales.Sendoffprintrequeststo:M.GamberaE-mail:mga@sunct.ct.astro.it2Keywords:cosmology:theory-cosmology:largescalestructureofUniverse-galaxies:formation1.IntroductionIthaslongbeenspeculate
7、donthefundamentalrolethattheangularmomentumcouldplayindeterminingthefateofcollapsingproto-structuresandseveralmodelshavebeenproposedtocorrelatethegalaxytypewiththeangularmomentumperunitmassofthestructureitself(Faber1982;Kashlinsky1982;Fall1983).Someauthors(seeBarrow&Sil
8、k1981;Szalay&Silk1983andPeebles1990)haveproposedthatnon-radialmotionswouldbeexpectedwithinadevelopingproto-clu
