Volume 644, December 2020
|Number of page(s)||6|
|Section||Letters to the Editor|
|Published online||08 December 2020|
Letter to the Editor
Modeling the statistics of the cold neutral medium in absorption-selected high-redshift galaxies
Institut d’Astrophysique de Paris, CNRS-SU, UMR7095, 98bis Bd Arago, 75014 Paris, France
Accepted: 20 November 2020
We present a statistical model of the selection function of cold neutral gas in high-redshift (z = 2.5) absorption systems. The model is based on the canonical two-phase model of the neutral gas in the interstellar medium and contains only one parameter for which we do not have direct observational priors: namely the central pressure of an L* halo at z = 2.5, P*. Using observations of the fraction of cold gas absorption in strong H I-selected absorbers, we were able to constrain P*. The model simultaneously reproduces the column density distributions of H I and H2, and we derived an expected total incidence of cold gas at z ∼ 2.5 of lCNM = 12 × 10−3. Compared to recent measurements of the incidence of C I-selected absorbers (EWλ 1560 > 0.4 Å), the value of lCNM from our model indicates that only 15% of the total cold gas would lead to strong C I absorption (EW > 0.4 Å). Nevertheless, C I lines are extremely useful probes of the cold gas as they are relatively easy to detect and provide direct constraints on the physical conditions. Lastly, our model self-consistently reproduces the fraction of cold gas absorbers as a function of NH I.
Key words: galaxies: high-redshift / galaxies: ISM / quasars: absorption lines
© J.-K. Krogager and P. Noterdaeme 2020
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