Surface photometry of galaxies in low density regions

¹ Tartu Observatory, EE2444 Tartu, Estonia, e-mail: vennik@aai.ee
² Max-Planck-Institut für Astronomie, Königstuhl, D-69117 Heidelberg, Germany e-mail: kuhn@mpia-hd.mpg.de
³ Universitätssternwarte München, Scheiner Str. 1, D-81679 München, Germany e-mail: hopp@usm.uni-muenchen.de
⁴ Bulgarian Academy of Sciences, Astronomical Institute, Bul. Zarigradsko Shose 72, 1784 Sofia, Bulgaria

Send offprint request to: J. Vennik

Received: 17 August 1995
Accepted: 27 September 1995

Abstract

We perform detailed surface photometry, based on B- and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies which were studied by Hopp et al. (1994) in the direction of three nearby voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different environments, and of a bright field galaxy sample. According to the obtained photometric characteristics, our sample is a mixture of intrinsically bright and faint galaxies, about 60% of them belonging to the bright subsample (). These bright ones show mean characteristics of typical Freeman's disks and are mainly located in the background of the observed voids. The faint subsample () has parameters typical for the low-surface-brightness (LSB) galaxies. There are a few well isolated galaxies both among the bright and faint subsamples. About 40% of studied galaxies reveal ellipticity and position angle variations along of the radius. The colour indices of the observed galaxies span over a wide range of 0.5-1.8 mag with a median value at 1.11 mag, rather blue. About 30% of the observed galaxies reveal radial colour gradients at a 5σ significance level. These galaxies show typically red centers and are getting bluer towards the periphery. The most isolated galaxies in our sample show relatively blue colours ( 0.8). About 40% of the studied galaxies have surface brightness profiles which can be described by the model of single exponential disk. 38% of our galaxies have more complicated profiles and either can be approximated by two exponentials or show the presence of a small bulge. 20% of the observed galaxies have central light depression and outer irregularities – typical for some dwarf galaxies. These profile type frequencies are similar to those of faint field galaxy sample. The evolutionary history of both the isolated and clustered galaxies obviously results in similar photometric and structural characteristics. Thus the photometric methods alone are inadequate for selecting galaxies with different isolation properties.