SURFACE PHOTOMETRY OF LOW SURFACE BRIGHTNESS GALAXIES

Low surface brightness (LSB) galaxies are galaxies dominated by an exp onential disc whose central surface brightness is much fainter than th e value of mu(B)(0) = 21.65 +/- 0.30 mag arcsec(-2) found by Freeman. In this paper we present broadband photometry of a sample of 21 late-t ype LSB galaxies. The median central surface brightness of the sample is mu(B)(0) = 23.2 mag arcsec(-2) and the median scale length is 3.2 k pc, showing that LSB galaxies are normal-sized galaxies. We find colou rs that are comparable to or bluer than those of the more widely studi ed 'normal' high surface brightness (HSB) galaxies. LSB galaxies are t herefore not faded discs that have no current star formation. The colo urs cannot on the other hand be ascribed entirely to metallicity effec ts, but we can explain them by assuming a sporadic star formation rate scenario. LSB galaxies hence appear to be unevolved and quiescent obj ects, which give us an insight into the evolution of galaxies in an un perturbed environment.