Color-absolute magnitude relation for E and S0 galaxies. III - Fully corrected photometry for 405 galaxies: Comparison of color distributions for E and S0 field and cluster galaxies

Colors in u - V and V - r, corrected for color-aperture gradient, galactic reddening, K dimming, and color-absolute magnitude effect, together with corrected V magnitudes, are listed for 405 galaxies, mostly of E and SO types, using the data and precepts of Paper II. Color distributions are compared for E and SO galaxies, divided into field and cluster members so as to test for effects of environment on stellar content and for color differences between the E and SO types. No differences were found, either between the E and 50 types or between the cluster and field memberships: The colors are independent of the environments represented here, whether the galaxies are disk (SO) or halo (E) systems. There is no change of fully corrected u - V colors with the apparent flattening of SO galaxies over the range of inclinations from 100 i < 900. The limit of A(u - V) < 0.03 mag over these inclinations shows that the optical depth in Vfor dust extinction is less than T = 0.01 for an average SO galaxy. The equality of color distributions for E and SO systems in and out of clusters is a necessary condition (1) that the stellar content of SO galaxies is similar to that of E systems, (2) that there has been no significant upper-main-sequence star formation in SO galaxies within the past 1O years, and (3) that the environment of the clusters studied here (Virgo, Coma, Centaurus, and Fornax) is not the determining factor in the formation and evolution of SO systems. And, although we also show that the equality of color distributions may also be a sufficient condition to rule out the sweeping of spirals to make SO's, there are two additional arguments that most SO galaxies form along the Hubble sequence rather than change into such forms as a consequence of some environmental process. The arguments start by noting (a) that many SO's are present in the isolated field, and (b) that the distribution of bulge-to-disk ratios among spirals and SO's differs. Such evidence indicates that stripping of spirals cannot produce the bulk of the 50 class, either in the field or in clusters. Subject headings: galaxies: clusters of - galaxies: evolution - galaxies: photometry - galaxies: structure