THE PROGENITORS OF LOCAL ULTRA-MASSIVE GALAXIES ACROSS COSMIC TIME: FROM DUSTY STAR-BURSTING TO QUIESCENT STELLAR POPULATIONS

Using the UltraVISTA catalogs, we investigate the evolution in the 11.4 Gyr since z = 3 of the progenitors of local ultra-massive galaxies (log (M-star/M-circle dot) approximate to 11.8; UMGs), providing a complete and consistent picture of how the most massive galaxies at z = 0 have assembled. By selecting the_progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56(-0.25)(+0.35) dex, 0.45(-0.20)(+0.16) dex, and 0.27(-0.12)(+0.08) dex from z = 3, z = 2, and z = 1, respectively, to z = 0. At z <1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At z > 1, the contribution from star-forming galaxies progressively increases, with the progenitors at 2 <z <3 being dominated by massive (M-star approximate to 2 x 10(11) M-circle dot), dusty (A(v) similar to 1-2.2 mag), star-forming (SFR similar to 100-400 M-circle dot yr(-1)) galaxies with a large range in stellar ages. At z = 2.75, similar to 15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that at least half of the stellar content of local UMGs was assembled at z > 1, whereas the remaining was assembled via merging from z similar to 1 to the present. Most of the quenching of the star-forming progenitors happened between z = 2.75 and z = 1.25, in good agreement with the typical formation redshift and scatter in age of z = 0 UMGs as derived from their fossil records. The progenitors of local UMGs, including the star-forming ones, never lived on the blue cloud since z = 3. We propose an alternative path for the formation of local UMGs that refines previously proposed pictures and that is fully consistent with our findings.