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 Lambda 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 M(v)13, with a rather sharp cutoff at the lower mass end, corresponding to virial velocities of similar to 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 (greater than or similar to 35 per cent) in haloes above the cutoff.