Supernova rate and the number of supernova remnants in M 31, M 33 andthe Galaxy.

The integrated thermal and nonthermal radio luminosities of M31, M33, and the Galaxy are used to estimate the rate of SNe tau(SN) and the number of SNRs in these galaxies. From the present-day mass functions (PDMFs), scaled with the total production rate of Ly-continuum photons, tau(SN) is obtained and compared with other estimates of this quantity. Comparison of the SN rates expected from the PDMFs and from statistics suggest that all stars more massive than about five solar masses become SN II. In that case, tau(SN) = 20 +9 or -5 yr in the Galaxy, 75 +48 or -31 yr in M33, and at least 22 +37 or -13 yr in M31. The minimum energy required to produce the observed nonthermal emission is consistent with a supernova remnant rate tau(SNR) = tau(SN) and a mean minimum energy of remnants of about 5 x 10 to the 50th erg. The total number of SNRs in M31, M33, and the Galaxy is 1000-10,000.