The assembly of massive galaxies from near-infrared observations of the Hubble Deep Field-South

We use a deep K-AB less than or equal to 25 galaxy sample in the Hubble Deep Field-South to trace the evolution of the cosmological stellar mass density from z similar or equal to 0.5 to z similar or equal to 3. We find clear evidence for a decrease of the average stellar mass density at high redshift, 2 less than or equal to z less than or equal to 3.5, that is 15(-5)(+25)% of the local value, 2 times higher than observed in the Hubble Deep Field-North. To take into account for the selection effects, we define a homogeneous subsample of galaxies with 10(10) M-.. less than or equal to M-* less than or equal to 10(11) M-.: in this sample, the mass density at z > 2 is 20(-5)(+20)% of the local value. In the mass-limited subsample at, the fraction of passively fading galaxies is at most 25%, although they can contribute up to about 40% of the stellar mass density. On the other hand, star-forming galaxies at z > 2 form stars with an average specific rate of at least [M/M-*] similar or equal to 4 x 10(-10) yr(-1), 3 times higher than the z less than or equal to 1 value. This implies that UV-bright star-forming galaxies are substancial contributors to the rise of the stellar mass density with cosmic time. Although these results are globally consistent with Lambda-CDM scenarios, the present rendition of semianalytic models fails to match the stellar mass density produced by more massive galaxies present at z > 2.