Integrated Colors of Bright Galaxies in the u, b, V System.

Abstract

Integrated colors in the U, B, V system and apparent diameters in a standard system are given for 148 mainly northern galaxies observed in by the author and Johnson at Flagstaff and by Tifft at Mount Wilson. The normal (U - B, B - V) sequences for galaxies are determined. The "face-on" colors (U - B)0, (B - V)0, i.e., corrected for tilt effects, vary as a function of morphological type and of the ratio A /D(0) of the field aperture to the "face-on" diameter; standard color-aperture relations are determined for normal galaxy types E, SO, Sa-Sb, Sbc, Sc, Scd, Sm-Im; galaxies of types E to Scd are redder in the center; types Sm and Im are bluer in the center. Departures from the standard relations are related to luminosity, red shift, and absorption effects. Dwarf ellipticals and lenticulars are systematically bluer than giants, and a close correlation is indicated between colors and absolute magnitude Mp > -17.5. Frequent color anomalies observed in some "blue" galaxies and especially their nuclei are clearly due to line emission; other anomalies observed in some blue nuclei, the center of Messier 87, and in Mayall's nebula are not due to line emission but to ultraviolet excess in the continuum. A close correlation exists between nuclear colors and the estimated spectral or color classes of Morgan; there is a weaker correlation with the luminosity classes of van den Bergh for type Sc only. Reduction formulae to the B - V system are given for the color4ndex systems of Stebbins and Whitford, Pettit, Holmberg, and Tiff t.