Limits on the star formation rates of z>2 damped Ly-alpha systems from H-alpha spectroscopy

Abstract

We present the results of a long-slit K-band spectroscopic search with CGS4 on UKIRT for H-alpha emission from the objects responsible for high-redshift (z > 2) damped Ly-alpha absorption systems. The objective was to measure the star-formation rates in these systems. However, no H-alpha emission was detected above our 3-sigma limits of f < 10E-19 W/m**2, corresponding to star formation rates < 10 M_sun/yr/h**2 (q_0=0.5). These upper limits are more meaningful than those from searches for Ly-alpha emission because the H-alpha line is unaffected by resonant scattering. For q_0=0.5 our limits are in conflict with the star formation rates predicted under the assumption that the high-z DLAs are the fully-formed galactic-disk counterparts of today&#39;s massive spiral galaxies. Deeper spectroscopy is needed to test this picture for q_0=0.0. A programme of NICMOS imaging observations currently underway, combined with VLT spectroscopy, will provide a detailed picture of the link between DLAs and young galaxies.