2. The sample and reduction
The sample of galaxies was taken from the ESO-LV catalog (Lauberts & Valentijn 1989). Here we will briefly describe the selection criteria with their justifications.
The galaxies were selected to have types Sa-Im so that we are not biasing ourselves to one person's/algorithm's classification scheme. The galactic latitudes were chosen so as to diminish foreground extinction ( ) and the inclinations were selected to be smaller than 50o to be not too sensitive to internal extinction. Furthermore, the surface brightnesses of the disks at half light radius were selected to be fainter than 23.8 B mag arcsec-2 and the diameters of the 26 B mag arcsec-2 isophotes were selected to lie between 1´ (pick large enough galaxies) and 3´ (chipsize limitation). These selection criteria resulted in approximately 600 galaxies. All these galaxies were inspected and selected on clean stellar foreground. From this subsample a random sample of galaxies which had central light concentrations was chosen. The result of this selection is that most of the galaxies in our sample have high surface brightness bulges embedded in low surface brightness disks. In the appendix R band images of our sample of LSB galaxies are shown. These images are presented using linear or exponential intensity scale (see captions) and central parts may be saturated. It can be seen from these images that we have roughly two types of bulge LSB galaxies in our sample. One type has a normal, round bulge and the other type has bars and rings. In Table 1 we list relevant sample information. Column 1 contains the ESO-LV name of the galaxy, Column 2 gives the right ascension (1950.0) and Column 3 the declination (1950.0). Column 4 gives the distance (Mpc) as taken from the ESO-LV catalog. Where not available, redshifts were determined with the single dish Parkes telescope (de Blok et al. 1999, in preparation). The inclination as derived from the data is given in Column 5 and total absolute B magnitudes as derived from the data are given in Column 6. Hubble types are listed in Column 7.
Table 1. Sample parameters.
All BVRI images were taken with the 0.9 meter Dutch Telescope at La Silla in October 1993, January 1994 and in March 1994. The CCD image reduction was done using standard procedures in the Image Reduction and Analysis Facility (IRAF) and the Groningen Image Processing SYstem (GIPSY; van der Hulst et al. 1992). The average seeing was and the images have a limiting surface brightness of B mag arcsec-2. The main source of errors in determining magnitudes and colors is the uncertainty in the sky level. We measured the sky level in five boxes placed on parts of the image free of stellar emission. The mean difference between the median sky levels in these boxes was used as an estimate for the error introduced by subtracting the sky. We determined the position angles and inclinations from smoothed R images. Stars and cosmic ray defects were blanked prior to any fitting. We used fixed position angles, inclinations and ellipse centers to make ellipse fits to the isophotes of the galaxies and to integrate along these ellipses. Each band of a galaxy is thus fit with the exact same model. All magnitudes and colors have been corrected for atmospheric and galactic extinction. Extinctions in the B band were taken from the NED database.
© European Southern Observatory (ESO) 1999
Online publication: November 16, 1999