Hanny's Voorwerp: a nuclear starburst in IC2497
  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. The e-VLBI observations detect two compact radio
sources with brightness temperatures in excess of 105 K, suggesting that they
are associated with an AGN located at the centre of the galaxy. We show that
IC2497 lies on the FIR-radio correlation and that the dominant component of the
18 cm radio flux density of the galaxy is associated with extended emission
confined to sub-kpc scales. IC 2497 therefore appears to be a luminous infrared
galaxy that exhibits a nuclear starburst with a total star formation rate
(assuming a Salpeter IMF) of ~ 70 M*/yr. Typically, vigorous star forming
galaxies like IC2497 always show high levels of extinction towards their
nuclear regions. The new results are in-line with the hypothesis that the
ionisation nebula "Hanny's Voorwerp", located ~15-25 kpc from the galaxy is
part of a massive gas reservoir that is ionised by the radiation cone of an AGN
that is otherwise obscured along the observer's line-of- sight.
