The properties and evolution of a K-band selected sample of massive galaxies at z ∼ 0.4-2 in the Palomar/DEEP2 survey

We present the results of a study on the properties and evolution of massive ( M-* > 10(11)M circle dot) galaxies at z similar to 0.4 - 2 utilizing Keck spectroscopy, near- infrared Palomar imaging, and Hubble, Chandra and Spitzer data covering fields targeted by the DEEP2 galaxy spectroscopic survey. Our sample is K- band selected and stellar mass limited, based on wide- area near- infrared imaging from the Palomar Observatory Wide- Field Infrared Survey, which covers 1.53 deg(2) to a 5 sigma depth of K-s,K-vega similar to 20.5. Our primary goal is to obtain a broad census of massive galaxies through measuring how their number and mass densities, morphology, as well as their star formation and active galactic nucleus content evolve from z similar to 0.4 - 2. Our major findings include: ( i) statistically the mass and number densities of M-* > 10(11)M circle dot galaxies show little evolution between z = 0 and 1 and from z similar to 0 to 2 for M-* > 10(11.5)M circle dot galaxies. We however find significant evolution within 1 < z < 1.5 for 10(11) M circle dot < M-* < 10(11.5)M circle dot galaxies. ( ii) After examining the structures of our galaxies using Hubble ACS imaging, we find that M-* > 1011M circle dot selected galaxies show a nearly constant elliptical fraction of similar to 70 - 90 per cent at all redshifts. The remaining objects tend to be peculiars possibly undergoing mergers at z > 0.8, while spirals dominate the remainder at lower redshifts. A significant fraction (similar to 25 per cent) of these early- types contain minor structural anomalies. ( iii) We find that only a fraction (similar to 60 per cent) of massive galaxies with M-* > 10(11)M circle dot are on the red sequence at z similar to 1.4, while nearly 100 per cent evolve on to it by z similar to 0.4. ( iv) By utilizing Spitzer MIPS imaging and [ O II] line fluxes we argue that M-* > 1011.5M circle dot galaxies have a steeply declining star formation rate ( SFR) density similar to ( 1 + z) (6). By examining the contribution of star formation to the evolution of the mass function, as well as the merger history through the CAS parameters, we determine that M-* > 10(11)M circle dot galaxies undergo on average 0.9+(0.7)(-0.5) - 0.5 major mergers at 0.4 < z < 1.4. ( v) We find that a high ( 5 per cent) fraction of all M-* > 10(11)M circle dot galaxies are X- ray emitters. Roughly half of these are morphologically distorted ellipticals or peculiars. Finally, we compare our mass growth with semi- analytical models from the Millennium Simulation, finding relative good agreement at z < 2 for the M-* < 10(11.5)M circle dot systems, but that the number and mass densities of M* > 10(11.5)M circle dot galaxies are underpredicted by a factor of > 100.