EXPLORING THE EVOLUTIONARY PATHS OF THE MOST MASSIVE GALAXIES SINCE z ∼ 2

We use Spitzer MIPS data from the FIDEL Legacy Project in the extended Groth strip to analyze the stellar mass assembly of massive (M > 10(11) M(circle dot)) galaxies at z < 2 as a function of structural parameters. We find 24 mu m emission for more than 85% of the massive galaxies morphologically classified as disks, and for more than 57% of the massive systems morphologically classified as spheroids at any redshift, with about 8% of sources harboring a bright X-ray-and/or infrared-emitting AGN. More noticeably, similar to 60% of all compact massive galaxies at z = 1-2 are detected at 24 mu m, even when rest-frame optical colors reveal that they are dead and evolving passively. For spheroid-like galaxies at a given stellar mass, the sizes of MIPS nondetections are smaller by a factor of similar to 1.2 in comparison with IR-bright sources. We find that disklike massive galaxies present specific SFRs ranging from 0.04 to 0.2 Gyr (1) at z < 1( SFRs ranging from 1 to 10M(circle dot) yr(-1)), typically a factor of 3-6 higher than massive spheroid-like objects in the same redshift range. At z > 1, and more pronouncedly at z > 1: 3, the median specific SFRs of the disks and spheroids detected by MIPS are very similar, ranging from 0.1 to 1 Gyr(-1) (SFR = 10-200M(circle dot) yr(-1)). We estimate that massive spheroid-like galaxies may have doubled ( at the most) their stellar mass from star-forming events at z < 2: less than 20% mass increase at 1: 7 < z < 2: 0, up to 40% more at 1.1 < z < 1.7, and less than 20% additional increase at z < 1. Disklike galaxies may have tripled ( at the most) their stellar mass at z < 2 from star formation alone: up to similar to 40% mass increase at 1: 7 < z < 2: 0, and less than 180% additional increase below z = 1.7 occurred at a steady rate.