IFU observations of luminous type II AGN - I. Evidence for ubiquitous winds

Abstract

We present observations of 17 luminous (log(L[O III]/L) > 8.7) local (z < 0.11) type II AGN. Our aim is to investigate the prevalence and nature of AGN-driven outflows in these galaxies by combining kinematic and ionization diagnostic information. We use non-parametric methods (e.g. W80, the width containing 80 per cent of the line flux) to assess the line widths in the central regions of our targets. The maximum values of W80 in each galaxy are in the range 400–1600 km s−1, with a mean of 790 ± 90 km s−1. Such high velocities are strongly suggestive that these AGN are driving ionized outflows. Multi-Gaussian fitting is used to decompose the velocity structure in our galaxies. 14/17 of our targets require three separate kinematic components in the ionized gas in their central regions. The broadest components of these fits have FWHM = 530–2520 km s−1, with a mean value of 920 ± 50 km s−1. By simultaneously fitting both the Hβ/[O III] and Hα/[N II] complexes, we construct ionization diagnostic diagrams for each component. 13/17 of our galaxies show a significant (>95 per cent) correlation between the [N II]/Hα ratio and the velocity dispersion of the gas. Such a correlation is the natural consequence of a contribution to the ionization from shock excitation and we argue that this demonstrates that the outflows from these AGN are directly impacting the surrounding ISM within the galaxies. Key words: galaxies: active – galaxies: evolution – galaxies: kinematics and dynamics Show more