2008ApJ...680...41D

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<logM_*<12 and 0<z<5. At z≳3, the average SFR is a power law of stellar mass (M{dot}_*∝M^0.6_*). The average SFR in massive objects at this redshift is 100-500 M_☉/yr. At z∼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 logM¹_*≳13 at z∼5 to logM¹_*∼10.9 at z∼0.5, according to M¹_*(z)=2.7x10¹⁰(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∼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_*≳11, mergers contribute 0.1-0.2/Gyr to the increase in number density. This corresponds 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.