Galaxy Size Problem at z=3 Simulated Galaxies Are Too Small(4)

Using state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations with a spatial resolution of 0.15 h-1kpc on a cosmological volume (20 h-1Mpc), we investigate the sizes of galaxies at z=3 in the standard cold dark matter model where re

concentratedinsmallcentralregionsofthesimulatedLBGs.Ontheotherhand,thesevelocitieshavenotbeenseeninanyrealgalaxieswithmeasuredrotationcurves.

Thisproblemmightberelatedtodisksizeproblematz=0(e.g,Navarro,Frenk,&White1995;Navarro&Steinmetz1997;Governatoetal.2004).Physicalprocessesathighredshiftthatmayberesponsiblefortheeventualresolutionofthisproblemmaybeless“diluted”atz=3.Therefore,onemaybeabletoobtainimportant“cleaner”cluestothenatureofthedarkmatterand/orimportantastrophysicalprocessesathighredshiftsusingz=3galaxies.Moreover,combiningobservationsatbothz=3andz=0mayprovidestillmorepowerfulconstraints.

2.SIMULATIONANDANALYSISMETHODS

Weperformcosmologicalsimulationswiththeadaptivemeshre nement(AMR)Eulerianhydrocode,Enzo(Bryan1999;Norman&Bryan1999;O’Sheaetal.2004).Firstweranalowresolutionsimulationwithaperiodicboxof20h 1MpconasideinaΛCDMuniversewithcosmologicalparametersconsistentwiththeWMAP3results:( m, Λ, b,h,σ8,ns)=(0.24,0.76,0.042,0.73,0.74,0.95).Weidenti edvirializeddarkmatterhalosinthissimulationatz=3andresimulated11ofthemostmassive20halosinasuiteof vehighresolutionsimulationsembeddedwithinthesame(20h 1Mpc)3boxusingthemultimassinitializationtechnique,whileevolvingtherestoftheboxatlowresolution.The vehighresolutionsimulationshaveavolumerangingfrom～(2.5h 1Mpc)3to～(6.4h 1Mpc)3.Withinresimulatedregions,thecellsizeoftherootgridis39h 1kpcandadditionalgridre nementsareallowedinanadaptivefashiontoreachamaximumleveloflmax=6,resultinginthemaximumspatialresolutionof0.61h 1kpc(comoving)or0.21kpc(proper)atz=3.Thedarkmatterparticlemassis4.6×106M⊙.ThesimulationsincludeametagalacticUVbackground(Haardt&Madau1996),adi use