Families of ellipsoidal stellar systems and the formation of dwarf elliptical galaxies

Abstract

Core radii and central surface brightnesses of bulges and elliptical galaxies are measured using CCD photometry obtained with the Canada-France-Hawaii Telescope (scale = 0''.22 pixel/sup -1/; seeing = 0''.45--1''.0 FWHM). The correlations between core parameters are derived and compared for ellipticals, bulges, dwarf spheroidal galaxies, dwarf irregular galaxies, and globular clusters. The results are as follows. 1. Ihe data confirm the existence of well-defined correlations between the core parameters of elliptical galaxies. More luminous ellipticals have larger core radii r/sub c/ and lower central surface brightnesses ..mu../sub 0v/. Galaxies with larger core radii have larger central velocity dispersions. The small, bright core of M32 is normal for a galaxy of M/sub B/ = -15.2. Radio ellipticals and brightest cluster galaxies satisfy the correlations. 2. The bulges of disk galaxies are basically similar to elliptical galaxies. Their cores have slightly smaller r/sub c/ and brighter ..mu../sub 0v/ than ellipticals of the same luminosity, because their nonisothermal profiles rise more rapidly toward the center and because they often contain extra nuclei superposed on their cores. 3. There is a large discontinuity between the parameter correlations for bright ellipticals, including M32, and those for dwarf spheroidals. Seven dE's in the Local Group andmore » three in the Virgo Cluster have core parameters which are correlated, but not as in ordinary ellipticals. More luminous dE's have larger r/sub c/ and brighter ..mu../sub 0v/.« less