The complex kinematics of galaxies in Hickson 62

Due to the high galaxy density, similar to that in the centers of rich galaxy clusters, and very low velocity dispersion, HCGs are the perfect environment where study galaxy-galaxy interactions. HCG 62 is one of the nearest (z=0.0137) Hickson compact galaxy groups, composed of 4 early-type galaxies. Using archival long-slit spectra obtained with FORS1 at VLT, we studied the stellar kinematics of the dominant elliptical NGC4778 of the HCG 62 group. We measured line-of-sight velocity distributions (LOSVDs) for NGC4778 by means of the Fourier Correlation Quotient method (FCQ), deriving the galaxy rotation curve and velocity dispersion. Figure 1 shows the rotation curve and the velocity dispersion profile of NGC4778. Our analysis reveals that NGC4778 possesses kinematical and morphological peculiarities, both in the central region (r < 5 arcsec) and in the outer halo. In the following we give a brief description of the observed kinematical properties. In the central region, the rotation curve points out the presence of a kinematically decoupled stellar component, shifted with respect to the photometric center. Such counterrotation is probably due to the accretion of material from an outside source with opposite angular momentum with respect to the host galaxy and is therefore likely due to a past merger event. In the outer halo we noted a distorsion in both the rotation curve and velocity dispersion profile. The velocity dispersion profile shows a rise in the SW direction, toward the galaxy NGC4776. This distorted kinematics in the outer halo can be either an artifact due to apparent superposition of the galaxies, or a dinamical effect, if the stars in NGC4778 are affected by the potential of NGC4776. The latter possibility may be the sign of an ongoing interaction, as expected in the secondary infall scenario.