Misc,
The Impact of Different Physical Processes on the Statistics of Lyman-limit and Damped Lyman-alpha Absorbers
(2013)cite arxiv:1307.6879Comment: 21 pages, 16 figures, submitted to MNRAS. The data used to produce all figures along with code to read it can be found here https://bitbucket.org/galtay/hi-cddf-owls-1.
Abstract
We compute the z = 3 neutral hydrogen column density distribution function
f(NHI) for 19 simulations drawn from the OWLS project using a post-processing
correction for self-shielding calculated with full radiative transfer of the
ionising background radiation. We investigate how different physical processes
and parameters affect the abundance of Lyman-limit systems (LLSs) and damped
Lyman-alpha absorbers (DLAs) including: i) metal-line cooling; ii) the
efficiency of feedback from SNe and AGN; iii) the effective equation of state
for the ISM; iv) cosmological parameters; v) the assumed star formation law
and; vi) the timing of hydrogen reionization . We find that the normalisation
and slope, D = d log10 f /d log10 NHI, of f(NHI) in the LLS regime are robust
to changes in these physical processes. Among physically plausible models,
f(NHI) varies by less than 0.2 dex and D varies by less than 0.18 for LLSs.
This is primarily due to the fact that these uncertain physical processes
mostly affect star-forming gas which contributes less than 10% to f(NHI) in the
the LLS column density range. At higher column densities, variations in f(NHI)
become larger (approximately 0.5 dex at NHI = 10^22 cm^-2 and 1.0 dex at NHI =
10^23 cm^-2) and molecular hydrogen formation also becomes important. Many of
these changes can be explained in the context of self-regulated star formation
in which the amount of star forming gas in a galaxy will adjust such that
outflows driven by feedback balance inflows due to accretion.
