A Large Survey for Very Low Surface Brightness Galaxies
Marshall, James J.
McGaugh, Stacy S.
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This dissertation presents the results of a survey for very low surface brightness galaxies in the field population. These galaxies have such low brightness per unit area on the night sky that they are difficult to detect and have been overlooked by many previous surveys. By covering a large area, approximately 91 deg^2, and reaching a low limiting surface brightness, approximately 25.4 Rmag arcsec^-2, we are able to detect these galaxies down to a surface brightness level that has not been well explored, allowing us to check and extend previous results. We describe the observations, data reduction procedure, astrometric and photometric calibrations which are performed using IRAF. The data analysis procedure involves detecting objects using the SExtractor program, performing a star/galaxy separation, and fitting the detected objects with a galaxy model using the GIM2D package for IRAF in order to measure their parameters. We perform a series of cuts on the objects to eliminate detections with potential problems, using the results of the data analysis steps to remove objects that are stellar-like, saturated, unresolved, have poor chi^2 values for the model fit, have very large disk scale lengths, or reached model fitting limits of 85 deg inclination and a bulge/total ratio of 0 or 1. We then selected objects that were brighter than 18.25 mag in R, had a bulge/total ratio B/T < 0.3 (disk dominated), and inclination i < 35 deg (relatively face-on) as our sample to study, a total of 757 objects. The results of our study indicate that the observed surface brightness distribution is peaked at a disk central surface brightness of 20.5 R mag arcsec^-2 and the intrinsic surface brightness distribution, obtained by applying a volume correction to the observed distribution, is consistent with a flat distribution out to approximately 24.25 R mag arcsec^-2. We also examine the number--magnitude relation for our detections, the assumption that galaxy disks are transparent by using the inclination as a measure of the transparency, and the relation between the disk and bulge scale lengths. The results are summarized and some possibilities for future study are presented.