Global Properties of Nearby Galaxies

Abstract

Surface photometry of nearby galaxies is among the research areas that gained most from the recent advances in ‘wide-field imaging’. In fact, the demand for an accurate measure of the night-sky level all around the target galaxy — a key step in galaxy surface photometry; see Fig. 1 in Capaccioli & de Vaucouleurs (1983) — calls for at least some images covering a field wider than the size of the object under study. So far, the small field of most CCD cameras attached to the Cassegrain foci of medium-size telescopes has prevented both the mapping of the galaxian outskirts and, a fortiori, a direct measurement of the sky background μb on the galaxy image itself. Indirect methods to estimate μb — blank-sky exposures, matching of growth curves to photoelectric integrated magnitudes, assumptions on the shape of the galaxian light profiles — have proven ineffective and/or methodologically questionable (Capaccioli 1989). Until large-format CCD chips or mosaics are routinely used, the only way out of these problems is either the use of focal reducers, whose optical complexity may however be incompatible with photometric accuracy, or of large-field photographic plates.