The stellar mass assembly of galaxies from z=0 to z=4:: Analysis of a sample selected in the rest-frame near-infrared with Spitzer

Using a sample of similar to 28,000 sources selected at 3.6-4.5 mu m with Spitzer observations of the Hubble Deep Field North, the Chandra Deep Field South, and the Lockman Hole ( surveyed area similar to 664 arcmin(2)), we study the evolution of the stellar mass content of the universe at 0 < z < 4. We calculate stellar masses and photometric redshifts, based on similar to 2000 templates built with stellar population and dust emission models fitting the ultraviolet to mid-infrared spectral energy distributions of galaxies with spectroscopic redshifts. We estimate stellar mass functions for different redshift intervals. We find that 50% of the local stellar mass density was assembled at 0 < z < 1 ( average star formation rate [SFR] 0.048 M-circle dot yr(-1) Mpc(-3)), and at least another 40% at 1 < z < 4 ( average SFR 0.074 M-circle dot yr(-1) Mpc(-3)). Our results confirm and quantify the "downsizing" scenario of galaxy formation. The most massive galaxies ( M > 10(12.0) M-circle dot) assembled the bulk of their stellar content rapidly ( in 1-2 Gyr) beyond z similar to 3 in very intense star formation events ( producing high specific SFRs). Galaxies with 10(11.5) < M < 10(12.0) M-circle dot assembled half of their stellar mass before z similar to 1.5, and more than 90% of their mass was already in place at z similar to 0.6. Galaxies with M < 10(11.5) M-circle dot evolved more slowly ( presenting smaller specific SFRs), assembling half of their stellar mass below z similar to 1. About 40% of the local stellar mass density of 10(9.0) < M < 10(11.0) M circle dot galaxies was assembled below z similar to 0.4, most probably through accretion of small satellites producing little star formation. The cosmic stellar mass density at z > 2.5 is dominated by optically faint ( R greater than or similar to 25) red galaxies ( distant red galaxies or BzK sources), which account for similar to 30% of the global population of galaxies, but contribute at least 60% of the cosmic stellar mass density. Bluer galaxies (e.g., Lyman break galaxies) are more numerous but less massive, contributing less than 50% of the global stellar mass density at high redshift.