Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.2001v&link_type=abstract
American Astronomical Society, AAS Meeting #211, #20.01; Bulletin of the American Astronomical Society, Vol. 39, p.770
Mathematics
Logic
Scientific paper
The evolution of the morphology-density relation (MDR) has been used elaborately to study the build-up of the early-type galaxy population in clusters of galaxies. Between z=1 and the present, with the aid of HST imaging, the early-type fraction in clusters has been found to evolve significantly. Recently, however, it has been demonstrated by Holden et al. (2007) that the observed evolution is driven by low-mass, star-forming galaxies, and that there is no significant evolution in the early-type fraction for stellar-mass limited samples. Following up on this work, we measure the evolution of the early-type galaxy fraction in the field (van der Wel et al. 2007). HST/ACS data from GOODS and the spectroscopic surveys in the GOODS-South field are used to construct a stellar-mass limited sample (log(M/Msol)>10.6) of several hundred galaxies at z=0.6-1. Morphologies are determined both visually and with an automated method, distinguishing two types (late and early). The SDSS provides the low-redshift baseline, and morphologies and stellar masses are determined for a sample of several thousand galaxies at z=0.020-0.045. We find that the early-type fraction down to our mass limit is 48%+/-7% in the z=0.8 sample, and 43+/-3% in the z=0.03 sample. In other words, we find no significant evolution in the field early-type galaxy fraction. Combining this with the constant early-type fraction in clusters, we conclude that the MDR has not evolved significantly in shape or normalization since z=0.8. We show that such lack of evolution is not inconsistent with other recent results such as the evolution in the stellar mass density of red-sequence galaxies and the strong decline in star formation activity over the same period. However, any evolution in the galaxy population has to conserve its morphological composition, at least insofar as only two morphological types are considered.
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