Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...20512902s&link_type=abstract
American Astronomical Society Meeting 205, #129.02; Bulletin of the American Astronomical Society, Vol. 36, p.1556
Astronomy and Astrophysics
Astronomy
Scientific paper
Damped Lyα Absorbers (DLAs) are those absorption-line systems with large neutral hydrogen column density, N(H I) ≥ 2×1020cm-2, seen against the emission of background QSOs. They are believed to be the progenitors of present day disk galaxies. In our galaxy or in the Magellanic clouds, all the clouds with N(H I)≥ 2×1020cm-2, have N(H2)> 1019cm-2. But roughly 80% of the DLAs do not have detected H2. We use chemistry and spectroscopy of molecular hydrogen, together with the fine structure excitations of C I and C II, to determine the physical properties of those z ˜ 2 DLAs with molecular hydrogen. We expanded the plasma simulation code Cloudy to do all the relevant formation, destruction, and physical processes involving molecular hydrogen self consistently with the thermal and ionization equilibrium of the gas. We find that the QSO dominated metagalactic radiation is sufficient to maintain a low H2 column density for gas density < 0.1 cm-3. For denser gas, a local radiation field, likely due to the star formation, is needed to reproduce the small H2 column densities.
Ferland Gary J.
Shaw Gargi
Srianand Raghunathan
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