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Cory R. Wagner
Department of Physics
University of Missouri-Kansas City
Advisor: Dr. Daniel H. McIntosh
Abstract
The projected axis ratio distributions of red galaxies as a function of stellar mass and redshift is studied. At low redshift, the preponderance of high-mass, non-star-forming galaxies with spheroidal axis ratios (b/a>0.6) is cited as strong evidence for their major-merger origin. The evolution of massive red galaxy shapes provides an important test for major merging being their primary growth channel. Starting with a stellar mass cut of 1010 Msun, we select 2500 galaxies with HST/ACS imaging and redshifts z>0.46 from the GEMS (Galaxy Evolution From Morphology and SEDs) and STAGES (Space Telescope A901/902 Galaxy Evolution Survey) surveys, and 4500 SDSS (z~0) galaxies. At low redshift, we find that the fraction of red spheroid galaxies increases steadily from 40% at the bimodal mass cut (3x1010 Msun) to 65% above 1x1011 Msun, consistent with the trends for spectroscopically-selected quiescent galaxies. Using a passively-evolving (U-V) color-mass cut to define red galaxies at z>0, we find no evolution in the fraction of red spheroids at moderate and high masses, implying that most additions to the massive red population at different cosmic epochs are from major mergers.
Cory Wagner is senior at the University of Missouri - Kansas City, majoring in Physics and Computer Science. He has been working with Dr. McIntosh in his Galaxy Evolution Group since May 2010. Upon graduating in the spring of 2012, Cory would like to continue his education by attending graduate school, and pursuing a master's degree in astrophysics
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