Radial stellar populations, kinematics, and photometry of the cD galaxy NGC 6086 in Abell 2162

Abstract

ABSTRACT We present a full study of deep optical long-slit spectroscopy and deep broad-band photometry of NGC 6086. We cover up to at least 3re in spectroscopy and 5re in photometry (re ≈ 22 arcsec in our V-band photometry). The envelope first appears in the photometric profile around 23 arcsec, and the velocity dispersion, age, metallicity, and Mg2 indices all show changes starting at about this radius suggesting that we are seeing two separate structures (ellipsoid and envelope) with different properties in the data. We do not find the kinematically decoupled core reported in Carter et al. The velocity dispersion profile rises from 300 km s−1 in the centre to 600 km s−1 at 40 arcsec, a similar tendency to that previously observed in NGC 6166. Populations indicate a trend from old metal-rich stars to younger metal-poorer ones as the radius increases. Line-index analysis indicates that the α-element proportion is high at all radii and that the Mg2 index declines relatively steeply with radius. The photometry shows the extended envelope with a Sérsic index of 0.6 and flat colour gradients. Previous measurements of the velocity dispersion of the galaxies in the cluster A2162 are in the range 300–420 km s−1 for only around 40 member galaxies, but there appears to be a radial discontinuity in the distribution of galaxies and a flattish distribution in radial velocity, implying that the kinematics of this cluster requires further investigation.