Fragmentation of Cosmologically Collapsed Layers

[摘要] Thefragmentationanddynamicsofpancake-likecollapsedlayersarediscussed.Thefragmentationtheoryforanisothermalgaslayerisextendedtothecaseofthetransverseexpansionorcontractionofalayerwithtwocomponents.Theexpansionofalayersuppressesthegrowthofaperturbationandthecontractionenhancestheperturbation.Itisshownthatthegrowthrateincreasesexponentiallywiththedecelerationofexpansion.Thecriticalwavenumberfortheinstabilityisalmostconstantforvariousratesoftheexpansion.Thelinearinteractionofaperturbationbetweenthecooledlayerandahotlayercomposedofdarkmatterchangesthegrowthrate.Thegrowthrateofthecooledlayerissuperiortothemaximumvalueofthegrowthrateinisolatedcaseswhenthescaleheightsofbothlayersarenotsodifferent.Thisfragmentationtheoryisappliedtocosmologicallycollapsedlayersthatwerecalculatedbynumericalsimulations.Thecooledlayersproducedbythecollapsewithtransverseexpansionhavenearlythesamedensityandtemperatureoverawidescalerangeofprimordialdensityfluctuations,λ=1–20Mpc.Themassoffragmentationisdeterminedbyevaluatingthegrowthtimeoftheperturbationandtheaccretiontimeofthecooledlayer.Thetypicalmassesofthefragmentationaredistributedoveranarrowmassscaleof107–8M⊙.Alargedynamicrangeofthecalculation,106–8,isrequiredtosimulatethecentralregionofthecollapsedlayerforthefluctuationwavelength,λ=10Mpc.Acalculationmethodwithextremelylargedynamicrangeisalsopresented.

[学科分类] 天文学(综合)

[关键词] "galaxies: formation";"hydrodynamics: fragmentation";"isothermal gas layer"