Galaxy Size Problem at z=3 Simulated Galaxies Are Too Small(6)

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

mpistheprotonmass,ΣZisthemasscolumndensityofmetalsinfrontofagivenstarparticle.Thefactor,F=5,ischosensothattheescapefractionintheUVbandisabout1/15(Meureretal.1997;Pettinietal.1998;Sawicki&Yee1998).Theconversionfrom

′isbasedonthedustextinctionlawproposedbyCalzettietal.(2000).Finally,AVtoAgobs

weapplyaGaussian lterwithFWHM=0.052′′totheprojectedluminositydensitymap(afterdustattenuation)tofacilitatedirectcomparisonbetweenthesimulatedimagesandtheHSTobservationsofhigh-zgalaxiesinFergusonetal.(2004).

3.RESULTS

Figure1showstheprojectedstellarmassdensityofaregionofcomovingsize(1.0h 1Mpc)2withadepthofcomoving2.4h 1Mpcatz=3,cutoutfromourlargesthighresolutionsimulationsub-volumeofsize～(6.4h 1Mpc)3.Theinsetsshowmagni edimagesofthefourmostmassivehalosinthedisplayedregionintheirprojectedluminositydensitydistributions.Foreachgalaxy,theimagesshow,fromlefttoright,intrinsic(beforedustattenuationisapplied),apparent(afterdustattenuation),andsmoothed(afterdustattenuationandPSF ltering)luminositydensities,respectively,allintheobservedg′-band.Ontheonehand,weseethatourhighresolutionpermitsformationofextremelydensestructures.Ontheotherhand,manyrichandsalientfeaturesproducedbycosmologicalprocesses,suchasmergersandtidaltails,paringtheleftmostandmiddlepicturesofeachrowoftheinsetssuggeststhatdustextinctionsigni cantlya ectstheobservedluminositydensitydistributionintheobservedg′-band.ThiscanbeunderstoodsimplyasaconsequenceoftheempiricalSchmidt-Kennicuttrelation(Kennicutt1998):gassurfacedensityincreasesmonotonicallyasstarformationratedensityincreases;andweassumedthatdustextinctionisproportionaltothemetalsurfacedensityhencegassurfacedensity.