SIMBAD references

Far-UV (2000 A) images of M 51 have been obtained with a balloon-borne telescope, at a resolution of 15". A comparison with an Hα image shows that the UV is systematically located downstream from Hα, the distance between the Hα maximum and the UV maximum is of 7"-11". The mean age of the stars emitting at these wavelengths is not the only reason for this displacement, the extinction also plays a role. Using the total gas content, an extinction correction has been applied to regions 33" in diameter. From UV fluxes, we computed local star formation rates (SFR) and the local star formation efficiency (SFE). The SFR is strongly correlated to the total gas surface density. There is a slight evidence that for R>5 kpc, the SFE has been influenced by the interaction with the companion galaxy NGC 5195. The mean azimuthal profiles of UV fluxes show that in the UV the arm/interarm contrast exhibits a similar, but stronger, contrast than at longer wavelengths. A skewness of the IMF towards massive stars is not necessary to explain the outward increase of the contrast.