SIMBAD references

The results of Hα photometry of a sample of early-type galaxies belonging to nearby compact groups are presented. Over 75% of the galaxies in the sample were detected in Hα, a result that we have interpreted as proof of the presence of a warm interstellar medium within them. Comparing the Hα luminosities of the galaxies in our sample with those of a sample of early-type galaxies from the field, we have found that field early-type galaxies are systematically fainter in Hα than the compact group ones for a given B absolute magnitude by ΔlogL_HαML_B~0.5. We suggest that the excess in the Hα emission within the groups is due to photoionization of gas by Lyman continuum photons emitted by massive stars. Recent massive star formation would be a consequence of the accretion by early-type galaxies of gas from the outer envelopes of gas-rich galaxies experiencing close passages across the group.