Recent Star Formation in Groups of Galaxies: HCG 31

Broadband UBVRI and narrowband Hα and continuum images have been obtained for the Hickson compact group HCG 31 as part of an ongoing program devoted to the study of the star formation properties of galaxies in these groups. A spatially resolved analysis for the (U-B), (V-I), and (B-I) color maps has been performed, as well as for the U band, Hα luminosity, and Hα equivalent width maps. Integrated luminosities in all the bands have been derived for all the galaxies in the group. Our results show that all the galaxies appear to have experienced their most recent star formation episode less than 10⁷ years ago, in good agreement with previous values found in the literature.

From the morphological point of view, three different kinds of star formation processes are taking place in the group: central starburst induced by a strong interaction, star formation induced by stripping of the gas due to the presence of a medium of higher pressure, and formation of a dwarf galaxy at the tip of one of the tidal tails.

Overall, the photometric properties of the central starburst in HCG 31 are consistent with model predictions for the early stages of a merger between late-type galaxies.