The contribution of star formation and merging to stellar mass buildup in galaxies

We present a formalism to reveal merging by subtracting the change in the galaxy stellar mass function (MF) due to mass-dependent star formation (SF) from the observed time derivative of the MF. We present the SF rate (SFR) in the FORS Deep Field as a function of stellar mass and time spanning 9 < log M-* < 12 and 0 < z < 5. At z greater than or similar to 3, the average SFR is a power law of stellar mass (M-* proportional to M-*(0.6)). The average SFR in massive objects at this redshift is 100-500 M-circle dot yr(-1). At z similar to 3, the SFR starts to drop at high masses. The break mass at which the SFR deviates from the power-law form decreases smoothly from logM(*)(1) greater than or similar to 13 at z similar to 5 to logM(*)(1) similar to 10.9 at z similar to 0.5, according to M-*(1)(z) = 2.7 x 10(10)(1 + z)(2.1) (downsizing). We directly observe a relationship between SF history and mass. More massive galaxies have steeper and earlier onsets of SF, higher peak SFR, followed by a shorter decay time. The SFR in high-mass galaxies at z similar to 4 can explain their rapid increase in abundance. Within large uncertainties, at most 0.8 effective major mergers per Gyr are consistent with the data, yet enough to transform most high-mass objects into ellipticals contemporaneously with their major SF episode. In contrast, at z < 1.5 and at M-* greater than or similar to 11, mergers contribute 0.1-0.2Gyr(-1) to the increase in number density. This corresponds to similar to 1 major merger per object a 1.5 > z > 0. At 10 < logM(*) < 11, galaxies are being preferentially destroyed at early times, while at later times the change in their numbers turns positive. This is an indication of the top-down buildup of the red sequence suggested by other recent observations.