VLBI Observations of NGC6240: resolving the double nuclei and radio supernovae

TL;DR

This study uses high-resolution VLBI imaging to resolve the double nuclei of NGC6240, revealing active galactic nuclei and supernovae, and providing insights into the galaxy's nuclear activity and starburst phenomena.

Contribution

First high-resolution multi-frequency VLBI observations of NGC6240 resolving nuclei and supernovae, supporting the coexistence of AGN and starburst activity in the galaxy.

Findings

Detected double nuclei and supernovae components.

Evidence of AGN activity at both nuclei.

Spectral analysis indicating free-free absorption.

Abstract

The European VLBI Network (EVN) has been used at two epochs in 2003 and 2009 to obtain multi-frequency high-resolution images of the merger galaxy NGC6240 in order to study the radio properties of all compact high-brightness components in the galaxy. Our observations at milli-arcsecond resolution detected the northern and southern nuclei and two radio components, which we interpret as long-lived luminous supernovae associated with the circum-nuclear starburst activity at the southern nucleus. The new VLBI data support the presence of an active galactic nucleus (AGN) together with starburst activity at the southern nucleus and provides some evidence for an AGN at the northern nucleus. The two nuclei both display an inverted spectrum at lower GHz frequencies. The spectrum of the southern nucleus indicates thermal free-free absorption on parsec scales, consistent with the presence of an AGN.