OASIS integral-field spectroscopy of the central kpc in 11 Seyfert 2 galaxies

TL;DR

This study uses integral-field spectroscopy to map the central regions of 11 Seyfert 2 galaxies, revealing complex gas kinematics, non-circular motions, and potential nuclear rings or flows, advancing understanding of active galactic nuclei environments.

Contribution

First detailed 2D spectroscopic mapping of NLRs in 11 Seyfert 2 galaxies, uncovering complex gas dynamics and structures not previously observed.

Findings

80% of galaxies show twisted S-shaped velocity contours.

Detected possible nuclear ring or radial gas flow in NGC 262.

Most emission lines exhibit asymmetric or multi-component profiles.

Abstract

We map narrow-line regions (NLRs) of 11 nearby Seyfert 2 galaxies with the optical integral-field spectrograph OASIS mounted at CFHT. We model emission-line profiles of 5 forbidden-line doublets and 2 Balmer lines, correcting for the underlying stellar absorption by reconstructing stellar spectra with synthetic evolutionary stellar population models. For each of the 11 targets, we present 2D maps of surface brightness in the observed emission lines, diagnostic line intensity ratios, gas kinematics (mean line-of-sight velocity and velocity dispersion), electron density, and interstellar reddening, and we plot spatially resolved spectral-diagnostic diagrams. The stellar data are represented by maps of mean line-of-sight (LOS) velocities and of the relative mass fractions of the young stellar populations. The gas velocity fields in 80% of the sample exhibit twisted S-shaped isovelocity contours, which are signatures of non-circular orbits and indicate non-axisymmetric gravitational potentials, gas motions out of the galactic plane, or possible outflows and inflows. Based on the kinematic measurements, we identified a possible nuclear ring or radial gas flow in NGC 262 (Mrk 348), not reported before. Eight of the eleven observed objects exhibit strongly asymmetric or multi-component emission-line profiles, in most cases confined to an elongated region passing through the galactic centre, perpendicular to the major axis of emission.