The nuclear activity of galaxies in the Hickson compact groups

In order to investigate the nuclear activity of galaxies residing in compact groups of galaxies, we present results of our optical spectroscopic program made at Okayama Astrophysical Observatory. We have performed optical spectroscopy of 69 galaxies belonging to 31 Hickson compact groups (HCGs) of galaxies. Among them, three galaxies have discordant redshifts and, moreover, spectral quality is too poor to classify another three galaxies. Therefore, we describe our results for the remaining 63 galaxies. Our main results are summarized as follows: (1) We have found in our sample 28 active galactic nuclei (AGNs), 16 H II nuclei, and 19 normal galaxies showing no emission line. We used this HCG sample for statistical analyses. (2) Comparing the frequency distributions of activity types between the HCGs and the field galaxies whose data are taken from Ho, Filippenko, & Sargent (382 field galaxies), we find that the frequency of H II nuclei in the HCGs is significantly less than that in the field. However, this difference may be due to selection bias to the effect that our HCG sample contains more early-type galaxies than the field, because it is known that H II nuclei are rarer in early-type galaxies than in later ones. (3) Applying a correction to this morphological bias to the HCG sample, we find that there is no statistically significant difference in the frequency of occurrence of emission-line galaxies between the HCGs and the field. This implies that the dense galaxy environment in the HCGs does not affect the triggering of either the AGN activity and the nuclear starburst. We discuss some implications on the nuclear activity in the HCG galaxies.