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 NGC 3351 obtained with the Multi-Element Radio Linked Inter-ferometer Network (MERLIN). We found 23 radio sources in this field, 6 of which are projected within the D25 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 coun-terpart 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