Axis Ratio Evolution of Red and Blue Galaxy Populations Since z=1

Details Axis Ratio Evolution of Red and Blue Galaxy Populations Since z=1 Axis Ratio Evolution of Red and Blue Galaxy Populations Since z=1

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733547w&link_type=abstract

American Astronomical Society, AAS Meeting #217, #335.47; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

We study the projected axis ratio distributions of red and blue galaxies as a function of stellar mass and redshift. 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; similar studies for star formers are lacking. 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 M>1e10 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. Using (U-V) color, we compare the red and blue fraction of b/a>0.6 galaxies in the local universe. We find that the fraction of red spheroid galaxies increases steadily from 40% at the bimodal mass cut (3e10 Msun) to 70% above 1e11 Msun, consistent with the trends for spectroscopically-selected quiescent galaxies. Moreover, the average axis ratios of blue galaxies increases with increasing stellar mass in a similar manner as for red 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.

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