The Role of Major Mergers and Nuclear Star Formation in Nearby Obscured Quasars

Abstract

We investigate the triggering mechanism and the structural properties of obscured luminous active galactic nuclei from a detailed study of the rest-frame B and I Hubble Space Telescope images of 29 nearby ( z ≈ 0.04–0.4) optically selected type 2 quasars. Morphological classification reveals that only a minority (34%) of the hosts are mergers or interacting galaxies. More than half (55%) of the hosts contain regular disks, and a substantial fraction (38%), in fact, are disk-dominated ( B/T ≲ 0.2) late-type galaxies with low Sérsic indices ( n < 2), which is characteristic of pseudo bulges. The prevalence of bars in the spiral host galaxies may be sufficient to supply the modest fuel requirements needed to power the nuclear activity in these systems. Nuclear star formation seems to be ubiquitous in the central regions, leading to positive color gradients within the bulges and enhancements in the central surface brightness of most systems.