2MASX J00423991+3017515: An offset active galactic nucleus in an interacting system

TL;DR

This study investigates an unusual active galactic nucleus (AGN) with a displaced position and shifted emission lines, suggesting it may be a recoiling black hole or part of a complex merger process.

Contribution

The paper presents the first optical, X-ray, and radio imaging of a unique AGN with spatial and spectral anomalies, proposing new scenarios for its nature.

Findings

AGN is spatially offset by 3.8 kpc from galaxy center.

Broad emission lines are blue-shifted by 1540 km/s relative to narrow lines.

Possible explanations include a recoiling black hole or a strong wind in a merger.

Abstract

We present a spectroscopic and imaging study of an abnormal active galactic nucleus (AGN), 2MASX J00423991+3017515. This AGN is newly identified in the hard X-rays by the Swift BAT All-Sky survey and found in an edge-on disk galaxy interacting with a nearby companion. Here, we analyze the first optical spectra obtained for this system (taken in 2011 and 2016), high-resolution imaging taken with the Hubble Space Telescope and Chandra X-ray Observatory, and 1" imaging with the Very Large Array. Two unique properties are revealed: the peaks of the broad Balmer emission lines (associated with gas orbiting very near the supermassive black hole) are blue shifted from the corresponding narrow line emission and host galaxy absorption by 1540 km/s, and the AGN is spatially displaced from the apparent center of its host galaxy by 3.8 kpc. We explore several scenarios to explain these features, along with other anomalies, and propose that 2MASX J00423991+3017515 may be an AGN with an unusually strong wind residing in a uniquely configured major merger, or that it is an AGN recoiling from either a gravitational "slingshot" in a three-body interaction or from a kick due to the asymmetric emission of gravitational waves following the coalescence of two progenitor supermassive black holes.