LLAMA: Nuclear stellar properties of Swift BAT AGN and matched inactive galaxies

TL;DR

This study compares the nuclear stellar properties of local AGNs and inactive galaxies using near-infrared observations, finding similar stellar kinematics and luminosity structures, with no significant differences between active and inactive types.

Contribution

It provides the first detailed spatially resolved stellar kinematic analysis of a matched sample of AGNs and inactive galaxies at small scales.

Findings

Stellar velocity fields show disk-like rotation in all galaxies.

No significant difference in stellar kinematics between AGNs and inactive galaxies.

Nuclear stellar light excess correlates with size-luminosity relation.

Abstract

In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.