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arXiv · 1504.07254

Neutral atomic-carbon QSO absorption-line systems at z>1.5: Sample selection, HI content, reddening, and 2175 A extinction feature

C. Ledoux·P. Noterdaeme·P. Petitjean·R. Srianand
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Abstract

We present the results of a search for cold gas at high redshift along QSO lines-of-sight carried out without any a priori assumption on the neutral atomic-hydrogen (HI) content of the absorbers. To do this, we systematically looked for neutral-carbon (CI) 1560,1656 transition lines in low-resolution QSO spectra from the SDSS database. We built up a sample of 66 CI absorbers with redshifts 1.5 21 compared to systematic DLA surveys. We study empirical relations between W_r(CI), N(HI), E(B-V) and the strength of the 2175 A extinction feature, the latter being detected in about 30% of the CI absorbers. We show that the 2175 A feature is weak compared to Galactic lines-of-sight exhibiting the same amount of reddening. This is probably the consequence of current or past star formation in the vicinity of the CI systems. We also find that the strongest CI systems tend to have the largest amounts of dust and that the metallicity of the gas and its molecular fraction is likely to be high in a large number of cases.

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C. Ledoux, P. Noterdaeme, P. Petitjean, R. Srianand. 2015-04-27. Neutral atomic-carbon QSO absorption-line systems at z>1.5: Sample selection, HI content, reddening, and 2175 A extinction feature. https://doi.org/10.1051/0004-6361/201424122

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