The bias of DLAs at z∼2.3: evidence for very strong stellar feedback in shallow potential wells

We discuss the recent Baryon Oscillation Spectroscopic Survey measurement of a rather high bias factor for the host galaxies/haloes of damped Lyman alpha absorbers (DLAs), in the context of our previous modelling of the physical properties of DLAs within the Λ cold dark matter paradigm. Joint modelling of the column density distribution, the velocity width distribution of associated low-ionization metal absorption, and the bias parameter suggests that DLAs are hosted by galaxies with dark matter halo masses in the range 10.5 < log Mv<13, with a rather sharp cutoff at the lower mass end, corresponding to virial velocities of ∼90 km s−1. The observed properties of DLAs appear to suggest very efficient (stellar) feedback in haloes with masses/virial velocities below the cutoff and a large retained baryon fraction (≳35 per cent) in haloes above the cutoff.