Revisiting the complex kinematics of ionized gas at the central region of NGC 1068: evidence of an additional active galactic nucleus?

TL;DR

This study reveals complex ionized gas kinematics in NGC 1068's nucleus, suggesting the presence of a second active galactic nucleus possibly resulting from a minor merger, based on spatially resolved data and multiwavelength analysis.

Contribution

It provides evidence for an additional AGN in NGC 1068 through detailed kinematic analysis and multiwavelength data, challenging the previous understanding of its nuclear activity.

Findings

Identification of symmetric gas blobs indicating outflow regions

Detection of zero velocity and high dispersion at the midpoint suggesting outflow launching

Optical spectropolarimetry supports the presence of a second AGN

Abstract

We present a spatially resolved analysis of ionized gas at the nuclear region of the nearby galaxy NGC 1068. While NGC 1068 has been known to have gas outflows driven by its active galactic nucleus (AGN), more complex kinematical signatures were recently reported, which were inconsistent with a rotation or simple biconical outflows. To account for the nature of gas kinematics, we performed a spatially resolved kinematical study, finding a morphologically symmetric pair of approaching and receding gas blobs in the northeast region. The midpoint of the two blobs is located at a distance of 180 pc from the nucleus in the projected plane. The ionized gas at the midpoint shows zero velocity and high velocity dispersion, which are characteristics of an outflow-launching position, as the two sides of a bicone, i.e., approaching and receding outflows are superposed on the line of sight, leading to no velocity shift but high velocity dispersion. We investigate the potential scenario of an additional AGN based on a multiwavelength data set. While there are other possibilities, i.e., X-ray binary or supernova shock, the results from optical spectropolarimetry analysis are consistent with the presence of an additional AGN, which likely originates from a minor merger.