Schedule Feb 17, 2012
On the Origin of the High Column Density Turnover in the HI Column Density Distribution
Denis Erkal (Univ. of Chicago)

The HI column density distribution provides a statistical measure of the properties of atomic hydrogen systems at both low and high redshift. We focus on features in the DLA regime (NHI > 10^20.3 cm^-2) where there are two features: a turnover at NHI ~ 10^21 cm^-2 which is present at both z=0 and z~3, and a lack of systems above NHI ~ 10^22 cm^-2 which is present at z=0. Through comparison of the column density distribution at low and high redshift, and comparison of local galaxies with varying metallicity, we argue that the turnover at NHI ~ 10^21 cm^-2 is not caused by the atomic to molecular transition. However, the transition could explain the lack of systems above NHI ~ 10^22 cm^-2. We consider the column density distribution which arises from randomly oriented copies of a single galaxy and find that it can reproduce the local column density distribution. Finally, we compare the column density distribution of our fully cosmological simulations to observations and find disagreement. We explore the reason for this discrepancy and argue that feedback can significantly affect the results.


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