2007A&A...474..443P

We present a detailed analysis of the Galaxy Stellar Mass Function (GSMF) of galaxies up to z=2.5 as obtained from the VIMOS VLT Deep Survey (VVDS). Our survey offers the possibility to investigate the GSMF using two different samples: (1) an optical (I-selected 17.5<I_AB<24) main spectroscopic sample of about 6500 galaxies over 1750arcmin² and (2) a near-IR (K-selected K_AB<22.34 and K_AB<22.84) sample of about 10200 galaxies, with photometric redshifts accurately calibrated on the VVDS spectroscopic sample, over 610arcmin². We apply and compare two different methods to estimate the stellar mass M_stars from broad-band photometry based on different assumptions about the galaxy star-formation history. We find that the accuracy of the photometric stellar mass is satisfactory overall, and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. We derive the cosmic evolution of the GSMF, the galaxy number density and the stellar mass density in different mass ranges. At low redshift (z≃0.2) we find a substantial population of low-mass galaxies (<10⁹M_☉) composed of faint blue galaxies (M_I-M_K≃0.3). In general the stellar mass function evolves slowly up to z∼0.9 and more rapidly above this redshift, in particular for low mass systems. Conversely, a massive population is present up to z=2.5 and has extremely red colours (M_I-M_K≃0.7-0.8). We find a decline with redshift of the overall number density of galaxies for all masses (59±5% for M_stars>10⁸M_☉ at z=1), and a mild mass-dependent average evolution (``mass-downsizing''). In particular our data are consistent with mild/negligible (<30%) evolution up to z∼0.7 for massive galaxies (>6x10¹⁰M_☉). For less massive systems the no-evolution scenario is excluded. Specifically, a large fraction redshift, with a decrease of a factor of 2.3±0.1 at z=1 and about 4.5±0.3 at z=2.5.