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Session 112 - Galaxy Surveys.
Oral session, Thursday, January 16
A Low Surface Brightness (LSB) galaxy survey of the Cancer and Pegasus galaxy clusters and the low density regime defined by the Great Wall, was undertaken between 14 October 1993 and 17 April 1996 using the University of Texas MacDonald Observatory 0.8m telescope and a LF1 2048x2048 CCD camera. 127 galaxies were found with \mu_B(0)\:\geq 22.0 mag/arcsec^2, 119 of which are previously unidentified. Structural parameters (\mu_B(0),\:\alpha,\:r_25,\:etc) and colors (Johnson/Cousins U,B,V,I, amp; R, when possible) were determined for the galaxies. The majority of these galaxies (80%) were well fit by an exponential profile, while the remaining were either fit by a king profile (17%) or were too clumpy to be fit by any curve (3%). The average central surface brightness of the sample is 23.06\pm0.20 mag/arcsec^2. The central surface brightness distribution of the galaxies is flat from 22.0 \mu_B(0) to 24.0 \mu_B(0), at which point a sharp drop-off is observed. By eliminating the possibility the drop-off is due to selection or distance effects, we show that it is highly likely the drop-off is due to the inability for extremely LSB galaxies to form in the cluster environment.
The colors of the galaxies in our survey range continuously from very blue (u-b=-0.56, b-v=0.37) to very red (u-b=0.65, v-i=2.2), and include a group of old galaxies which show evidence for recent star formation. This survey for LSB galaxies is the first to discover a significant population of objects with red colors. Since galaxies must fade and redden, the absence of LSB red disks in previous surveys has been puzzling and may be the result of a significant selection effect associated with photographic survey data. At the same time the continuous range of colors from very blue to very red clearly show that at the present epoch, LSB galaxies define a wide range of evolutionary states. Finally, the number density of the galaxies in our survey, when corrected for selection effects, is flat to increasing (depending upon the \mu_lim used) through \mu_B(0) = 25.6 mag/arcsec^2, showing that LSB galaxies are important contributors to the overall baryon content of the universe.
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