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Paper: The Contribution of Star Formation and Merging to Stellar Mass Buildup in Galaxies
Volume: 399, Panoramic Views of Galaxy Formation and Evolution
Page: 260
Authors: Drory, N.; Alvarez, M.
Abstract: 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 (Drory & Alvarez 2008). 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 > 3, the average SFR is a power law of stellar mass (dM/dt*M0.6*). The average SFR in massive objects at this redshift is 100 – 500 Myr−1. 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 log M1* > 13 at z ∼ 5 to log M1* ∼ 10.9 at z ∼ 0.5, according to logM1*(z) = 2.7 × 1010 (1 + z)2.1 (downsizing). 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 logM* > 11, mergers contribute 0.1 – 0.2 Gyr−1 to the increase in number density. This corresponds to ∼ 1 major merger per object at 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.
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