The surface brightness of 1550 galaxies in Fornax: automated galaxy surface photometry - II

Abstract

We present a survey of a complete sample of galaxies in the region of the Fornax cluster. Measurements with the APM machine are used to derive the observed distribution of galaxy surface brightness for 1550 objects. Corrections for surface brightness dependent selection effects are then made in order to estimate the true distribution. We find that the sample (with |$16.6\leqslant m_{\text{APM}}\leqslant19.1$|⁠) is divided into two distinct populations. The ‘normal’ galaxies with extrapolated central surface brightness SX ≲ 22.5 Bμ form a uniformly distributed background of field galaxies. Their surface brightness distribution peaks at SX = 21.75 Bμ and has a width ∼2 mag. Low surface brightness galaxies (SX ≳ 22.5 Bμ), on the other hand, are strongly clumped about the cluster centre. There appear to be few low surface brightness field galaxies. The central surface brightness distribution for these cluster galaxies is essentially flat in the accessible range 22.5–24.2 Bμ and their numbers rise rapidly towards faint magnitudes (for a distance modulus of 31.0 for Fornax, the absolute magnitude range studied is from −14.4 to −11.9).