2-D Photometry

Abstract

Strictly speaking, the projected images of all astronomical objects appear to possess a two-dimensional light distribution. In fact, due to the resolution con- straints of the earth atmosphere and of the observational equipments (telescopes as well as detectors), even point- like sources such as distant stars and extremely remote galaxies are spread into blurrincr disks which sometimes call for a 2-D photometric investigation (see, e.g., Ne- well 1979, Agnelli et al. 1979, Zou et al. 1981, Kron 1983). However, this review will be focused only to the the scientific and technical aspects of 2-D photometry of classical extended sources, i.e. sources whose angu- lar scale length is considerably larger than the charac- teristic length of the Point Spread Function (hereafter PSF). Among the class of celestial sources sharing this property (and to which most of the following considera- tions apply) we will select gralaxies. Recent reviews on the same subject were published by Kormendy 1980, 1982, de Vaucouleurs 1983, Capaccioli 1984. Finally, we want to remark that our discussion refers only to studies in the optical waveband (from UV to near IR); observational methodologies and data reduction can differ very much in the other bands (X and gamma rays and radio domain) and thus require a separate analysis.