The Gemini Deep Deep Survey: III. The Evolution of Galaxy Stellar Masses

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  • 5 January 2004
Abstract
We present the observed evolution in the stellar mass density locked up in giant galaxies over 0.81. The cosmological mass density in the most massive objects (M_star>10^10.8 solar masses) declines only very slowly to z=2. In contradiction to the paradigm of standard hierarchical formation based models, the bulk of the stellar mass in large galaxies was assembled at high redshifts rather than recently. We find no evidence for a dependence of the evolutionary rate on mass, again in contrast with a hierarchical assembly picture. The mass density follows an evolutionary path whose shape agrees well with that independently determined from integration of previous measurements of cosmic star-formation history. This represents the first precision measurement of mass assembly over 1<z<2 and demonstrates that new ingredients are essential in models of galaxy formation to push back the epoch of star-formation in giant galaxies to higher redshifts.

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