An extremely prolific supernova factory in the buried nucleus of the starburst galaxy IC 694

TL;DR

This study uses high-resolution radio imaging to uncover a dense cluster of young supernovae in the dust-obscured nucleus of galaxy IC 694, revealing a recent intense starburst activity.

Contribution

It provides the first detailed radio imaging evidence of a prolific supernova factory in the obscured core of IC 694, demonstrating the effectiveness of VLBI in detecting hidden supernovae.

Findings

Discovered 26 compact radio sources in the galaxy's nucleus.

Identified at least three young, long-lasting radio supernovae with unusual properties.

Supported a recent starburst event less than 15 million years ago.

Abstract

Context. The central kiloparsec of many local Luminous Infra-red Galaxies are known to host intense bursts of massive star formation, leading to numerous explosions of core-collapse supernovae (CCSNe). However, the dust-enshrouded regions where those supernovae explode hamper their detection at optical and near-infrared wavelengths. Aims. We investigate the nuclear region of the starbust galaxy IC 694 (=Arp 299-A) at radio wavelengths, aimed at discovering recently exploded CCSNe, as well as to determine their rate of explosion, which carries crucial information on star formation rates, the initial mass function and starburst scenarios at work. Methods. We use the electronic European VLBI Network to image with milliarcsecond resolution the 5.0 GHz compact radio emission of the innermost nuclear region of IC 694. Results. Our observations reveal the presence of a rich cluster of 26 compact radio emitting sources in the central 150 pc of the nuclear starburst in IC 694. The large brightness temperatures observed for the compact sources indicate a non-thermal origin for the observed radio emission, implying that most, if not all, of those sources are young radio supernovae (RSNe) and supernova remnants (SNRs). We find evidence for at least three relatively young, slowly-evolving, long-lasting RSNe (A0, A12, and A15) which appear to display unusual properties; suggesting that the conditions in the local circumstellar medium (CSM) play a significant role in determining the radio behaviour of expanding SNe. Their radio luminosities are typical of normal RSNe, which result from the explosion of Type IIP/b and Type IIL SNe. All these results yield support for a recent (less than 10-15 Myr) instantaneous starburst in the innermost regions of IC 694.