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P. Cassata (University of Padova), L. Guzzo (INAF, Osservatorio Astronomico di Brera), A. Franceschini (University of Padova), COSMOS Collaboration
We analyze the relationships among galaxy morphological type, color, stellar mass and the environment within a subset of the COSMOS survey, in a sky region around a complex large-scale structure at z=0.73. Using photometric redshifts, we isolate a redshift slice with < z > ~ 0.7 and investigate the role of the environment and stellar mass in determining the color and the morphology of luminous galaxies (those used to define the morphology-density relation at z=0). The color-magnitude diagram is clearly bimodal, with early types dominating the red sequence and late types populating the bluer part. In the low-density regions we find a number of ``blue ellipticals'', populating mainly low density regions, that we interpret as the result of recent mergers. These objects are not massive enough as to be the progenitors of future red-sequence objects. The red part of the color-magnitude diagram is compatible with an high redshift origin for early-type galaxies, and we discuss the scenario in which the red sequence could be fed the via mergers of galaxies in the blue tail. Moreover, we find that the colors of early-type galaxies do not depend on the enviroment. Finally, and most importantly, we find that mass rather than environment seems to be the primary factor in establishing galaxy morphology. Early- and late-type galaxies considered separately in fact show mass distribution functions that are invariant in shape with local density, while changing their amplitude as a function of environment.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.