A Multi-wavelength Study of the Turbulent Central Engine of the Low-mass AGN hosted by NGC404

TL;DR

This study uses multi-wavelength observations to resolve and analyze the low-mass AGN in NGC404, revealing a compact radio source likely driven by a confined jet, providing insights into low-mass black hole activity.

Contribution

First resolved the nuclear radio emission in NGC404, constraining its spectral index and suggesting a jet-driven outflow in a low-mass AGN.

Findings

Resolved a 17 pc extended radio source at the galaxy's center.

Identified the radio emission as optically-thin synchrotron radiation.

Evidence suggests a jet-driven outflow associated with the AGN.

Abstract

The nearby dwarf galaxy NGC404 harbors a low-luminosity active galactic nucleus (AGN) powered by the lowest-mass (< 150,000 solar-masses) central massive black hole (MBH) with a dynamical mass constraint currently known, thus providing a rare low-redshift analog to the MBH "seeds" that formed in the early Universe. Here, we present new imaging of the nucleus of NGC404 at 12-18 GHz with the Karl G. Jansky Very Large Array (VLA) and observations of the CO(2-1) line with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we have successfully resolved the nuclear radio emission, revealing a centrally peaked, extended source spanning 17 pc. Combined with previous VLA observations, our new data place a tight constraint on the radio spectral index and indicate an optically-thin synchrotron origin for the emission. The peak of the resolved radio source coincides with the dynamical center of NGC404, the center of a rotating disk of molecular gas, and the position of a compact, hard X-ray source. We also present evidence for shocks in the NGC404 nucleus from archival narrowband HST imaging, Chandra X-ray data, and Spitzer mid-infrared spectroscopy, and discuss possible origins for the shock excitation. Given the morphology, location, and steep spectral index of the resolved radio source, as well as constraints on nuclear star formation from the ALMA CO(2-1) data, we find the most likely scenario for the origin of the radio source in the center of NGC404 to be a radio outflow associated with a confined jet driven by the active nucleus.