The Evolution of Passive Galaxies since z=1: Major Mergers vs Secular Processes

We study the evolution of the red sequence and the blue cloud since z ~ 1 to present in GOODS-S field for M_B ≤ -20 and M_* ≥ 10¹⁰ M_⊙ selected galaxies. We segregate the galaxies in early-type galaxies (ET, E/S0/Sa), and late-type galaxies (LT, Sb-Irr) by their position in the concentration-asymmetry plane, while in passive and star-forming by their rest-frame NUV - R color and their 24μm properties.

We find that red sequence (passive early types) comoving number density rise with cosmic time in both samples, while blue cloud (star-forming late types) number density descent in luminosity-selected samples and increase in mass-selected sample. We also find a third population that comprises star-forming early-type galaxies.

Comparing the observed evolution with the disk-disk (wet) major merger rate in GOODS-S, we infer that only ~20% of M_* ≥ 10¹⁰ M_⊙ red sequence galaxies appeared since z = 1 can be explained by this kind of mergers, suggesting that minor mergers and secular evolution are the main processes in the red sequence evolution of M_* ≥ 10¹⁰ M_⊙ galaxies since z ~ 1.