Colors and the Byurakan classification of galaxies

Abstract

It is shown that the galaxies of the Byurakan classes 2 and 5, which belong to the morphological subtypes Sa, Sab, Sb, and Sbc (including the SB galaxies), are on average somewhat bluer than the galaxies of classes 3 and 4 of these same subtypes. Among galaxies of the classes 2, 5, and 2s, objects with excess ultraviolet radiation are found rather more frequently than among galaxies of classes 3 and 4. Whereas Sa, Sab, Sb, and Sbc galaxies of classes 3 and 4 are scarcely different from one another in their mean B -V and U -B, Sc and Scd galaxies of class 4, as also of classes 2 and 5, are on average bluer than class 3. In comparison with the latter, among Sc and Sod ~alaxies of classes 2, 4, and 5, there are rather more objects with negative U -B. These facts, together with the already known indicators of activity in galaxies of the classes 2, 4, 5, and 2s, in their turn point to active processes taking place in galaxies with diffuse, split, semistellar, or starlike nuclei.