The surface brightness profiles of elliptical and supergiant galaxies

Abstract

The surface brightness profiles of a sample of supergiant and elliptical galaxies were studied. The original data were gathered by Dr. G.A. Welch, who also wrote the program (PROFIL) for the data reduction. This study was undertaken at the suggestion of Dr. Welch, to investigate the shape of the brightness profiles of several supergiant galaxies, and to determine if they fit the relation recently suggested for cD galaxies by Bahcall (1977). Data from a number of elliptical galaxies was also processed using the same methods as a check on the reduction procedures. The cD galaxies were calibrated directly using photoelectric photometry, while the profiles of the elliptical galaxies were put on an absolute scale utilizing a photographic transfer method. Based on comparisons with published profiles for several of the galaxies, the resulting brightness profiles were found not to contain any significant errors due to calibration or reduction procedures. The elliptical galaxies (with one exception) all fit the de Vaucouleurs (1953) relation for elliptical, as expected. The exception, a galaxy identified as A-29/52 AC, appears to have a brightness profile which shows an extended halo, and also fits very well the relation suggested by Bahcall for the profiles of cD galaxies. AC does not appear to be located in a cluster. Three of the four cD galaxies studied show good agreement with the Bahcall relation. The fourth, the cD galaxy in Abell 401, displays a much shallower decline in brightness than the other program cD galaxies, and with respect to the Bahcall relation. It is thus concluded that all supergiant galaxies do not fit the Bahcall relation, and that there are other objects, not classified as cD galaxies, whose light distributions do seem to fit the Bahcall relation. This finding holds important implications for the investigation of the dynamic history of supergiant galaxies, as the evolutionary paths of galaxies whose brightness profiles obey a particular empirical relation may be different from those galaxies whose profiles do not.