On the influence of the environment in the star formation rates of a sample of galaxies in nearby compact groups

We present the results of a study of the star formation rates (SFRs) of a s ample of disk galaxies in nearby compact groups compared with the SFRs of a sample of field galaxies. For this purpose, H alpha luminosities and equiv alent widths were derived for the galaxies of our sample. A direct comparis on of the equivalent widths and H alpha luminosities, normalized to the B l uminosities and estimated area of the galaxies of both samples, yields the result that the median values of these quantities are almost identical for both samples, although the distributions for the compact-group sample are b roader around the mean value than was found in the field galaxy sample. Thi s result can be explained by assuming that although interactions between ga laxies in compact groups can alter the SFRs, the median value of the normal ized SFRs is preserved, being almost indistinguishable from the correspondi ng value for field galaxies. Measuring the global L-H alpha/L-B of the grou ps, including early-type galaxies, we find that most of the groups that sho w the highest level of L-H alpha/L-B with respect to a set of synthetic gro ups built out of field galaxies show tidal features in at least one of thei r members. Finally, we have explored the relationship between the ratio L-H alpha/L-B and several relevant dynamical parameters of the groups: velocit y dispersion, crossing time, radius, and the mass-to-luminosity ratio, find ing no clear correlation. This suggests that the exact dynamical state of a group does not control the SFR of the group as a whole. Our results are co mpatible with a scenario for compact groups of galaxies in which the dark m atter of the group is arranged in a common halo, therefore preventing a fas t collapse of the galaxies.