VLT-FORS2 optical imaging and spectroscopy of 9 luminous type 2 AGN at 0.3<z<0.6: I. Ionized gas nebulae

TL;DR

This study uses VLT-FORS2 optical imaging and spectroscopy to analyze 9 luminous type 2 AGNs at redshifts 0.3<z<0.6, revealing high merger rates, diverse ionized gas structures, and insights into AGN and star formation interactions.

Contribution

First detailed optical imaging and spectroscopy of a lower luminosity sample of type 2 AGNs at intermediate redshifts, highlighting merger prevalence and ionized gas properties.

Findings

78% show morphological signs of interactions or mergers

Extended emission line structures are common and varied in origin

AGN processes dominate nuclear gas excitation

Abstract

We present optical imaging and long slit spectroscopic observations of 9 luminous type 2 AGNs within the redshift range 0.3<z<0.6 based on 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%) show morphological evidence for interactions or mergers in the form of disturbed morphologies and/or peculiar features such as tidal tails, amorphous halos, 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 sample 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.