On the HI content, dust-to-gas ratio and nature of MgII absorbers

Details On the HI content, dust-to-gas ratio and nature of MgII absorbers On the HI content, dust-to-gas ratio and nature of MgII absorbers

2008-03-06

arxiv.org/abs/0803.0745v2

Astronomy and Astrophysics

Astrophysics

9 pages, minor changes to match the version accepted for publication in MNRAS

Scientific paper

10.1111/j.1365-2966.2008.14225.x

We estimate the mean dust-to-gas ratio of MgII absorbers as a function of rest equivalent width W_0 and redshift over the range 0.5 and W_0, an indicator of gas velocity dispersion. By combining these results with recent dust-reddening measurements we show that the mean dust-to-gas ratio of MgII absorbers does not appreciably depend on rest equivalent width. Assuming that, on average, dust-to-gas ratio is proportional to metallicity, we find its redshift evolution to be consistent with that of L^star galaxies from z=0.5 to 1.4 and we show that our constraints disfavor dwarf galaxies as the origin of such absorbers. We discuss other scenarii and favor galactic outflows from ~L^star galaxies as the origin of the majority of strong MgII absorbers. Finally, we show that, once evolutionary effects are taken into account, the Bohlin et al. relation between A_V and N_H is also satisfied by strong MgII systems down to lower column densities than those probed in our Galaxy.

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