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Using quasar absorption lines to probe cold gas in high redshift galaxies

Abstract : Quasar absorption lines are a powerful tool to study the interstellar medium(ISM) in the galaxies. We study a sample of 66 z >1.5 absorbers selected based on the presence of strong CI absorption lines in SDSS spectra and observed with the ESO-VLT spectrograph X-shooter/UVES. I study 17 systems that are re-observed by X-shooter. I derive metallicities, depletion onto dust, extinction by dust and analyse the absorption from MgII, MgI, CaII and NaI that are redshifted into the near infrared wavelength range. I detect 9 CaII absorptions with W(CaII λ3934) > 0.23 Å out of 14 systems. I detect 10 NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width (W(NaI λ5891) = 0.68 Å) is larger than what is observed in local clouds with similar HI column densities but also in z<0.7 CaII systems detected in the SDSS. The systematic presence of NaI absorption in these CI systems strongly suggests that the gas is neutral and cold, maybe part of the diffuse molecular gas in the ISM of high-redshift galaxies. The MgII absorptions are spread over more than Δv ~ 400 km/s for half of the systems; three absorbers have Δv > 500 km/s. The kinematics is strongly perturbed for most of these systems which probably do not arise in quiet disks and must be close to regions with intense star formation activity. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments. We detect molecular hydrogen in all the systems within the detection limit.
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  • HAL Id : tel-02454222, version 1

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Siwei Zou. Using quasar absorption lines to probe cold gas in high redshift galaxies. Astrophysics [astro-ph]. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS181⟩. ⟨tel-02454222⟩

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