Radio Identification of UGC Galaxies: Starbursts and Monsters

Radio identifications of galaxies in the Uppsala General Catalogue of Galaxies with δ < +82^deg^ were made from the Green Bank 1400 MHz sky maps. Every source having peak flux density S_P_ >= 150 mJy in the ~12 arcmin FWHM map point-source response and position < 5 arcmin in both coordinates from the optical position of any UGC galaxy was considered a candidate identification to ensure that very extended (up to 1 Mpc) and asymmetric sources would not be missed. Maps in the literature or new 1.49 GHz VLA C array maps made with 18 arcsec resolution were used to confirm or reject candidate identifications. The resulting list of 176 confirmed identifications should be complete, reliable, and suitable for statistical investigations of radio emission from nearby (D < 300 Mpc for H_0_ = 50 km s^-1^ Mpc^-1^) galaxies of all morphological types. The distribution of the infrared-radio parameter u=log (S_60 micron_/S_1400 MHz_) for most radio-selected spirals is roughly Gaussian with mean <u> = +2.02 +/- 0.02 and rms width σ_u_ = 0.20. These values agree with <u> = +2.15 and σ_u_ <= 0.3 found for infrared- selected galaxies since a difference {DELTA}u~(3/2) ln (10)σ^2^_u_ = 0.14 is expected from frequency selection alone. The small observed value of {DELTA}u implies that populations of radio-selected spiral galaxies are very similar to infrared-selected galaxies, not "normal" (optically selected) galaxies. Radio sources powered by "starbursts" can be effectively distinguished from those whose energy sources are "monsters" (e.g., super- massive black holes) by three radio and infrared criteria: ( 1) radio morphology, (2) u>= 1.6, and (3) infrared spectral index α_IR_=log (S_60 micron_/S_25 micron_)/log (60/25) >= +1.25.