THE STELLAR MASS FUNCTION OF GALAXIES TO z ∼ 5 IN THE FORS DEEP AND GOODS-S FIELDS

We present a measurement of the evolution of the stellar mass function (MF) of galaxies and the evolution of the total stellar mass density at 0 < z < 5, extending previous measurements to higher redshift and fainter magnitudes (and lower masses). We use deep multicolor data in the Fors Deep Field (FDF; I-selected reaching IAB ∼ 26.8) and the GOODS-S/CDFS region (K-selected reaching KAB ∼ 25.4) to estimate stellar masses based on fits to composite stellar population models for 5557 and 3367 sources, respectively. The MF of objects from the K-selected GOODS-S sample is very similar to that of the I-selected FDF down to the completeness limit of the GOODS-S sample. Near-IR selected surveys hence detect the more massive objects of the same principal population as do I-selected surveys. We find that the most massive galaxies harbor the oldest stellar populations at all redshifts. At low z, our MF follows the local MF very well, extending the local MF down by a decade to 108 M⊙. Furthermore, the faint end slope is consistent with the local value of α ∼ 1.1 at least up to z ∼ 1.5. Our MF also agrees very well with the MUNICS and K20 results at z . 2. The MF seems to evolve in a regular way at least up to z ∼ 2 with the normalization decreasing by 50% to z = 1 and by 70% to z = 2. Objects with M > 1010 M⊙which are the likely progenitors of todays L> L galaxies are found in much smaller numbers above z ∼ 2. However, we note that massive galaxies with M > 1011 M⊙are present even to the largest redshift we probe. Beyond z ∼ 2 the evolution of the mass function becomes more rapid. We find that the total stellar mass density at z = 1 is 50% of the local value. At z = 2, 25% of the local mass density is assembled, and at z = 3 and z = 5 we find that at least 15% and 5% of the mass in stars is in place, respectively. The number density of galaxies with M > 1011 M⊙ evolves very similarly to the evolution at lower masses. It decreases by 0.4 dex to z ∼ 1, by 0.6 dex to z ∼ 2, and by 1 dex to z ∼ 4. Subject headings: surveys — cosmology: observations — galaxies: mass function — galaxies: evolution — galaxies: fundamental parameters