VLT FORS2 optical imaging and spectroscopy of nine luminous type 2 AGN at 0.3 < z < 0.6 - I. Ionized gas nebulae

A. Humphrey, M. Villar Martín, C. Ramos Almeida, C. N. Tadhunter, S. Arribas, P. S. Bessiere, A. Cabrera Lavers

Abstract
We present optical imaging and long slit spectroscopic observations of nine luminous type 2 active galactic nuclei (AGN) within the redshift range 0.3 < z < 0.6 based on Very Large Telescope Focal Reducer and Low Dispersion Spectrograph (VLT FORS2) data. Most objects (6/9) are high luminosity Seyfert 2, and three are type 2 quasars (QSO2), with our sample extending to lower luminosity than previous works. Seven out of nine objects (78 per cent) show morphological evidence for interactions or mergers in the form of disturbed morphologies and/or peculiar features such as tidal tails, amorphous haloes, or compact emission line knots. The detection rate of morphological evidence for interaction is consistent with those found during previous studies of QSO2 at similar z, suggesting that the merger rate is independent of AGN power at the high end of the AGN luminosity function. We find the emission line flux spatial profiles are often dominated by the often spatially unresolved central source. In addition, all but one of our samples is associated with much fainter, extended line emission. We find these extended emission line structures have a variety of origins and ionization mechanisms: star-forming companions, tidal features, or extended ionized nebulae. AGN related processes dominate the excitation of the nuclear gas. Stellar photoionization sometimes plays a role in extended structures often related to mergers/interactions.

Keywords
galaxies: active – galaxies: evolution – galaxies: interactions – galaxies: ISM – galaxies: nuclei – quasars: emission lines

Monthly Notices of the Royal Astronomical Society
Volume 454, Page 4452
December 2015

DOI: 10.1093/mnras/stv2177
ADS Bibliographic code: 2015MNRAS.454.4452H