Simulations of Damped Lyα and Lyman Limit Absorbers in Different Cosmologies: Implications for Structure Formation at High Redshift

Abstract

We use hydrodynamic cosmological simulations to study damped Lya (DLA) and Lyman limit (LL) absorption at redshifts z \ 2È4 in Ðve variants of the cold dark matter scenario : COBE-normalized (CCDM), cluster-normalized (SCDM), and tilted (n \ 0.8) models, as well as open (OCDM) and ) m \ 1 Ñat (LCDM) models. Our standard simulations resolve the formation of dense concentrations ) m \ 0.4 of neutral gas in halos with circular velocity km s~1 for and 90 km s~1 for v c º v c,res B 140 ) m \ 1 at z \ 2 ; an additional LCDM simulation resolves halos down to km s~1 at z \ 3. ) m \ 0.4, v c,res B 50 We Ðnd a clear relation between H I column density and projected distance to the center of the nearest galaxy, with DLA absorption usually conÐned to galactocentric radii less than 10È15 kpc and LL absorption arising out to projected separations of 30 kpc or more. If we consider only absorption in the halos resolved by our standard simulations, then all Ðve models fall short of reproducing the observed abundance of DLA and LL systems at these redshifts. To estimate the absorption from lower mass halos, we Ðt a power law to the relation between absorption area a and halo circular velocity in our v c simulations and extrapolate using the Jenkins et al. halo mass function ; we do not apply this method to the TCDM model because it has too few halos at the level resolved by our simulation. In the two LCDM simulations, for which DLA results agree well in the mass regime of overlap, the mean cross section for DLA absorption is much larger than the simple estimate based a B n(0.3R vir )2, a D n(0.1R vir )2 on collapse of the baryons to a centrifugally supported disk is the halo virial radius). The cross (R vir sections for LL absorption are with a dependence on numerical resolution at the D25% a B n(0.6R vir )2, level. Detailed examination provides further evidence of nonequilibrium e †ects on absorption cross section : for example, individual absorbers can be slightly smaller in more massive halos because gas sinks deeper into the potential wells, but more massive halos nonetheless have larger average cross sections because they are more likely to have multiple gas concentrations. Our extrapolation procedure implies that all four models are consistent with the observed abundance of DLA systems if the Ðtted extends to km s~1, and they may produce too much absorption if the relation continues a(v c ) v c B 50È80 to km s~1. Matching the observed abundance of LL systems requires absorption in halos down v c [ 40 to km s~1. Our results suggest that LL absorption is closely akin to DLA absorption, arising v c B 30È50 in less massive halos or at larger galactocentric radii but not caused by processes acting on a radically di †erent mass scale. Robust tests of cosmological models against the observed amount of high column density absorption will require simulations of representative volumes that resolve halos at the low-mass limit where they cease to harbor high column density absorbers, km s~1. 30 [ v c [ 60

The physical nature of the most metal-poor damped Lyman α systems

“…The large galaxy sample size and the high resolution are indispensable to study DLAs in detail statistically. The simulation has the following cosmological parameters that are consistent with the WMAP7-normalized (Komatsu et al 2011 Cen (2012) compares our simulation to other studies, mostly based on smoothed particle hydrodynamics (SPH) simulations as of the year 2012 (Gardner et al 1997a,b;Gardner et al 2001;Haehnelt, Steinmetz & Rauch 1998;Nagamine et al 2004;Nagamine 2004;Nagamine et al 2007;Pontzen et al 2008;Tescari et al 2009;Hong et al 2010). The paper shows that our simulations demonstrate broad agreement with the previous SPH simulations, and the differences between our simulations and the SPH simulations can be attributed to different simulation box sizes and our inclusion of self-shielding in the simulation.…”

An integral field spectroscopic survey for high redshift damped Lyman-α galaxies

“…Larger DLA galaxy sizes of 10-15 kpc at 2 < z < 4 are inferred by other simulations (Gardner et al 2001). A possibility for the difference between observations and simulations is that the simulations assume a single disk scenario, while DLA galaxies could exist in groups (Hou et al 2005).…”

The Clustering of Galaxies around Threez∼ 3 Damped Lyα Absorbers

“…Although simulations of DLA properties exist (e.g., Katz et al 1996b;Gardner et al 2001;Nagamine et al 2004), no prediction of the DLA-LBG cross-correlation has been published. In N. Bouché et al (2004, in preparation) we use the TreeSPH cosmological simulations of Katz et al (1996a) to measure the ''theoretical'' DLA-LBG cross-correlation.…”

“…Despite numerous attempts to reproduce the properties of DLAs (e.g., Katz et al 1996b;McDonald & Miralda-Escudé 1999;Mo et al 1999;Gardner et al 2001;Nagamine et al 2004;Okoshi et al 2004) in numerical simulations or semianalytical models, there are no predictions of the clustering of galaxies around DLAs. In N. Bouché et al (2004, in preparation) we discuss the cross-correlation of LBGs around DLAs in smoothed particle hydrodynamical (SPH) numerical simulations.…”