Sub-arcsecond radio continuum mapping in and around the spiral galaxy
  NGC3351 using MERLIN
  We report sub-arcsecond scale radio continuum observations of a field of 35
by 22 arcmin centred in NGC3351 obtained with the Multi-Element Radio Linked
Interferometer Network (MERLIN). We found 23 radio sources in this field, 6 of
which are projected within the D$_{25}$ isophote of the galaxy, and 3 are
located inside the central 100 arcsec in radius. Two of these three are
significantly extended, while the third one is relatively compact. This one is
the only source with a previously detected counterpart at other wavelengths and
could constitute the radio counterpart of a young supernova remnant. The other
two are probably related to jets from a background AGN. We are not able to
detect individual supernovae or SNRs in the central region ($r<600$ pc) of the
galaxy. This could imply that the ionising populations of the circumnuclear
star-forming regions (CNSFRs) are too young (less than a few Myr) to host
supernovae. Also the diffusion length of the relativistic electrons in the ISM
associated with the SN from previous events of star formation seems to be
larger than our maximum resolution of 50 pc in radius. Detecting the thermal
bremsstrahlung emission from the circumnuclear HII regions probably requires
deeper observations.
