1999MNRAS.309..875B

We present the results of a long-slit K-band spectroscopic search for Hα emission from eight damped Lyα absorbers (DLAs) at z>2 with the goal of measuring the star formation rates in these systems. For each system we searched for compact sources of Hα emission within a solid angle 11x2.5arcsec² (44x10h^–2kpc², for q₀=0.5, H₀=100h km.s^–1.Mpc^–1). No Hα emission was detected above 3σ limits in the range (6.5-16)x10^–20W.m^–2, equivalent to star formation rates of 5.6-18h^–2 M_☉.yr^–1, for a standard initial mass function, assuming the lines are spectrally unresolved (<650km.s^–1 FWHM). We compare these results against the predictions of the models of Pei & Fall of the global history of star formation, under two different simplifying hypotheses: (i) the space density of DLAs at z=2.3 is equal to the space density of spiral galaxies today (implying DLA discs were larger in the past, the `large-disc' hypothesis); (ii) the sizes of DLAs at z=2.3 were the same as the gas sizes of spiral galaxies today (implying DLA discs were more common in the past, the `hierarchical' hypothesis). Compared with the previous most sensitive spectroscopic search, our sample is twice as large, our limits are a factor greater than two deeper, and the solid angle surveyed is over three times as great. Despite this, our results are not in conflict with either the large-disc hypothesis, because of the limited solid angle covered by the slit, or the hierarchical hypothesis, because of the limited sensitivity.