Asymmetry Measures for Quasi-Stellar Objects and Companions

An asymmetry index is derived from ellipse fitting to galaxy images that gives weight to faint outer features and is not strongly redshift dependent. These measures are made on a sample of 13 Two Micron All Sky Survey quasi-stellar objects (QSOs) and their neighbor galaxies, and a control sample of field galaxies from the same wide-field imaging data. The QSO host-galaxy asymmetries correlate well with visual tidal interaction indices previously published. The companion galaxies have somewhat higher asymmetry than the control galaxy sample, and their asymmetry is inversely correlated with the distance from the QSO. The distribution of QSO-companion asymmetry indices is different from that for matched control field galaxies at the ~95% significance level. We present the data and discuss this evidence for tidal and other disturbances in the vicinity of QSOs.

Based on observations obtained with the Canada-France-Hawaii Telescope, which is operated by CNRS of France, NRC of Canada, and the University of Hawaii.