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Abstract: For a mass-selected sample of 66544 galaxies with photometric redshifts fromthe Cosmic Evolution Survey COSMOS, we examine the evolution of starformation activity as a function of stellar mass in galaxies. We estimate thecosmic star formation rates SFR over the range 0.2 < z < 1.2, using therest-frame 2800 A flux corrected for extinction. We find the mean SFR to be astrong function of the galactic stellar mass at any given redshift, withmassive systems log M-MSun > 10.5 contributing less by a factor of ~ 5to the total star formation rate density SFRD.Combining data from the COSMOS and Gemini Deep Deep Survey GDDS, we extendthe SFRD-z relation as a function of stellar mass to z~2. For massive galaxies,we find a steep increase in the SFRD-z relation to z~2; for the less massivesystems, the SFRD which also increases from z=0 to 1, levels off at z~1. Thisimplies that the massive systems have had their major star formation activityat earlier epochs z > 2 than the lower mass galaxies.We study changes in the SFRDs as a function of both redshift and stellar massfor galaxies of different spectral types. We find that the slope of the SFRD-zrelation for different spectral type of galaxies is a strong function of theirstellar mass. For low and intermediate mass systems, the main contribution tothe cosmic SFRD comes from the star-forming galaxies while, for more massivesystems, the evolved galaxies are the most dominant population.

Autor: Bahram Mobasher 1, T. Dahlen 2, A. Hopkins 3, N. Z. Scoville 4, P. Capak 5, R. M. Rich 6, D. B. Sanders 7, Eva Schinnerer 8, Oliv


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