HCG 16: A High Concentration of Active Galaxies in the Nearby Universe

In the course of an extensive campaign to measure radial velocities of galaxies in a selected sample of compact groups photometrically studied by de Carvalho et al., we report the discovery of a system very rich in starburst galaxies and active galactic nuclei. This is the system HCG 16 of Hickson's catalog of compact groups. The seven brightest galaxies form a kinematical group with biweighted estimate mean velocity of VBI = 3959 ± 66 km s-1, dispersion σBI = 86 ± 55 km s-1, a median radius ⟨R⟩ = 0.197 Mpc, a mean density of ⟨D⟩ = 217 galaxies Mpc-3, and a total absolute magnitude of MB = -22.1. From their spectral characteristics, we have identified one Seyfert 2 galaxy, two LINERs, and three starburst galaxies. Thus, HCG 16 appears to be a dense concentration of active galaxies. In our sample of 17 Hickson groups, HCG 16 is unique in this regard, which suggests that it is an uncommon structure in the nearby universe.