Key points are not available for this paper at this time.
We use a sample of 8298 galaxies observed as part of the Hubble Space Telescope (HST) H160-band GOODS NICMOS Survey (GNS) to construct the galaxy stellar mass function both as a function of redshift and as stellar mass up to z= 3.5. Our mass functions are constructed within the redshift range z= 1–3.5 and consist of galaxies with stellar masses of M*= 1012 M⊙ down to nearly dwarf galaxy masses of M*= 108.5 M⊙ in the lowest redshift bin. We discover that a significant fraction of all massive M* > 1011 M⊙ galaxies are in place up to the highest redshifts we probe, with a decreasing fraction of lower mass galaxies present at all redshifts. This is an example of ‘galaxy mass downsizing’, and is the result of massive galaxies forming before lower mass ones, and not just simply ending their star formation earlier as in traditional downsizing scenarios, whose effect is seen at z 2. We furthermore show that, although there is a downsizing such that high-mass galaxies are nearer their z= 0 values at high redshift, this turns over at masses M*∼ 1010 M⊙, such that the lowest mass galaxies are more common than galaxies at slight higher masses, creating a ‘dip’ in the observed galaxy mass function. We argue that the galaxy assembly process may be driven by different mechanisms at low and high masses, and that the efficiency of the galaxy formation process is lowest at masses M*∼ 1010 M⊙ at 1 < z < 3. Finally, we calculate the integrated stellar mass density for the total, blue and red populations. We find the integrated stellar mass density of the total and blue galaxy population is consistent with being constant over z= 1–2, while the red population shows an increase in integrated stellar mass density over the same redshift range.
Mortlock et al. (Mon,) studied this question.