Is an obscured AGN at the centre of the disk galaxy IC 2497 responsible for Hanny's Voorwerp?

TL;DR

This study uses VLBI and MERLIN radio observations to investigate the presence of an active galactic nucleus in IC 2497 and its potential role in illuminating Hanny's Voorwerp, revealing compact radio components indicative of AGN activity.

Contribution

The paper provides new high-resolution radio observations that confirm the existence of multiple compact components associated with an AGN in IC 2497, supporting the jet-illumination hypothesis.

Findings

Detection of two compact radio components C1 and C2 near the galaxy center.

C1 shows elongation aligned with Hanny's Voorwerp, suggesting a jet connection.

Both components exhibit brightness temperatures indicative of AGN activity.

Abstract

We present the results of VLBI and MERLIN observations of the massive disk galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy. Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact radio component (C1) at the centre of IC 2497. The brightness temperature of C1 was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations presented here, re-confirm the existence of C1 but also reveal the existence of a second compact component (C2) located about 230 milliarcseconds to the North-East of C1. The brightness temperature of C2 is measured to be greater than 1.4E5 K, suggesting that both components may be related to AGN activity (e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations show both components. C1 is shown to be compact with a slight elongation along the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in an almost perpendicular direction to the direction of the Voorwerp. Our results continue to support the hypothesis that IC 2497 contains an Active Galactic Nucleus (AGN), and that a jet associated with this AGN clears a path that permits ionising radiation from the AGN to directly illuminate the emission nebula.