SIMBAD references

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 HI-selected absorbers, we were able to constrain P^*. The model simultaneously reproduces the column density distributions of HI and H₂, and we derived an expected total incidence of cold gas at z∼2.5 of l_CNM=12x10^–3. Compared to recent measurements of the incidence of CI-selected absorbers (EW_λ1560>0.4Å), the value of l_CNM from our model indicates that only 15% of the total cold gas would lead to strong CI absorption (EW>0.4Å). Nevertheless, CI 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 N_HI.