Submitted to ApJ Preprint typeset using L ATEX style emulateapj v. 5/14/03 THE REST-FRAME OPTICAL LUMINOSITY DENSITY, COLOR, AND STELLAR MASS DENSITY OF THE UNIVERSE FROM Z=0 TO Z=3 1

We present the evolution of the rest-frame optical luminosity density j, the integrated rest-frame optical color, and the stellar mass density, ?*, for a sample of Ks band-selected galaxies in the Hubble Deep Field-South (HDF-S). We derived j in the rest-frame U, B, and V bands and found that j increases by a factor of 1.9 ? 0.4, 2.9 ? 0.6, and 4.9 ? 1.0 in the V, B, and U rest-frame bands, respectively, between redshifts of 0.1 and 3.2. We derived the luminosity-weighted mean cosmic (U-B)rest and (B-V)rest colors as a function of redshift. The colors bluen almost monotonically with increasing redshift; at z = 0.1, the (U-B)rest and (B-V)rest colors are 0.16 and 0.75, respectively, while at z = 2.8 they are -0.39 and 0.29, respectively. We derived the luminosity-weighted mean M/L, using the correlation between (U-V)rest and log M/L that exists for a range in smooth star formation histories (SFHs) and moderate extinctions. We have shown that the mean of individual M/L estimates can overpredict the true value by ~70%, while our method overpredicts the true value by only ~35%. We find that the universe at z ~ 3 had ~10 times lower stellar mass density than it does today in galaxies with L > 1.4 ? 1010 h L?. Half of the stellar mass of the universe was formed by z ~ 1-1.5. The rate of increase in ?* with decreasing redshift is similar to but above that for independent estimates from the HDF-N, but it is slightly less than that predicted by the integral of the SFR(z) curve.