Astronomy and Astrophysics
نویسندگان
چکیده
Detailed analysis of the spectral lines from two low redshift damped Lyman alpha absorbers (DLA) confirms that they are a heterogeneous population. Both systems have low metal abundances of approximately 0.05 to 0.1 solar. The abundance pattern of the DLA at z = 1.15 towards HE 0515-4414 shows dust depletion comparable to that found in our Galaxy, while the system at z = 0.68 towards HE 1122-1649 shows abundance ratios resembling metal-poor halo stars with no dust depletion, for a comparable H i column. Constraints for N/Fe and N/Si also hint at z = 0.68 DLA as a galaxy with recent star formation. The trend of increasing C i/H i with decreasing z is discussed. Only weak absorption from highly-ionized species associated with the DLA at moderate z have been detected and it probably originates in regions distinct from the low ionization gas. The low-ion profiles show very complex structures and are too large to be explained by the rotation of a disk: the system at z = 0.68 spans over ∼ 300 km s−1 and the z = 1.15 DLA presents substructure over more than 700 km s−1 , the largest velocity extent found up to date for a DLA.
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