The cold gas content of post-starburst galaxies

Post-starburst galaxies, or E+A galaxies, are characterized by optical spectra showing strong Balmer absorption lines, indicating a young stellar population, and little or no emission lines, implying no active star formation. These galaxies are interpreted as a transitional population between star-forming, disc-dominated galaxies and spheroidal quiescent, non-star-forming galaxies. Here, we present single dish H I 21-cm emission-line measurements of a sample of 11 of these galaxies at redshifts z < 0.05. We detect H I emission in six of the E+A galaxies. In combination with earlier studies, the total number of E+A galaxies with measured cold gas components is now 11. Roughly half of the E+As studied so far have detectable H I. The gas fractions of these galaxies, measured with respect to their stellar mass, are between 1 and 10 per cent and are at the high end of the gas fractions measured in gas-bearing early-type galaxies and typically lower than seen in late-type galaxies with comparable stellar masses. This finding is consistent with the idea that E+As are currently evolving from the blue cloud to the red sequence. However, the question of why the star formation has ceased in these galaxies while a significant gas reservoir is still present can only be answered by higher spatial resolution observations of the cold gas.