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 _ { \odot } ) } \approx 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 ^ { +0.35 } _ { -0.25 } dex , 0.45 ^ { +0.16 } _ { -0.20 } dex , and 0.27 ^ { +0.08 } _ { -0.12 } 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 } \approx 2 \times 10 ^ { 11 } M _ { \odot } ) , dusty ( A _ { V } \sim 1–2.2 mag ) , star-forming ( SFR \sim 100–400 M _ { \odot } yr ^ { -1 } ) galaxies with a large range in stellar ages .
At z = 2.75 , \sim 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 \sim 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 .