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

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 Voorwerp in the proximity of the galaxy. Earlier short-track 18 cm observations with e-VLBI at l 18 cm, detected a compact radio component (C1) at the centre of IC 2497. The brightness temperature of C1 was measured to be > 4 10 5 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 > 1.4 10 5 K, suggesting that both components may be related to AGN activity (e.g. a radio core and jet hotspot). Lower resolution l 18 cm 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.