On the H i content, dust-to-gas ratio and nature of Mg ii absorbers |
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Authors: | Brice Ménard Doron Chelouche |
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Institution: | Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario, M55 3H8, Canada |
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Abstract: | We estimate the mean dust-to-gas ratio of Mg ii absorbers as a function of rest equivalent width W 0 and redshift over the range 0.5 < z < 1.4 . Using the expanded Sloan Digital Sky Survey/ Hubble Space Telescope sample of low-redshift Lyman-α absorbers, we first show the existence of a 8σ correlation between the mean hydrogen column density 〈 N H i 〉 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 Mg ii 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 ★ galaxies from z = 0.5 to 1.4, and we show that our constraints disfavour dwarf galaxies as the origin of such absorbers. We discuss other scenarios and favour galactic outflows from ~ L ★ galaxies as the origin of the majority of strong Mg ii 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 Mg ii systems down to lower column densities than those probed in our Galaxy. |
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Keywords: | ISM: dust extinction galaxies: haloes quasars: absorption lines |
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