Hanny's Voorwerp: Evidence of AGN activity and a nuclear starburst in
  the central regions of IC 2497
  We present high- and intermediate resolution radio observations of the
central region in the spiral galaxy IC 2497, performed using the European VLBI
Network (EVN) at 18 cm, and the Multi-Element Radio Linked Interferometer
Network (MERLIN) at 18 cm and 6 cm. We detect two compact radio sources, with
brightness temperatures above 10e5 K, suggesting that they are related to AGN
activity. We show that the total 18 cm radio emission from the galaxy is
dominated neither by these compact sources nor large-scale emission, but
extended emission confined within a sub-kpc central region. IC 2497 therefore
appears as a typical luminous infrared galaxy that exhibits a nuclear starburst
with a massive star formation rate (M > 5M_solar) of 12.4 M_solar/yr. These
results are in line with the hypothesis that the ionisation nebula "Hanny's
Voorwerp" at a distance of approx. 15-25 kpc from the galaxy is ionised by the
radiation cone of the AGN.
