The Properties and Evolution of a K-band Selected Sample of Massive Galaxies at z ∼ 0.4 − 2 in the Palomar/DEEP2 Survey

نویسندگان

  • C. J. Conselice
  • K. Bundy
  • I. Trujillo
  • A. Coil
  • P. Eisenhardt
  • R. S. Ellis
  • A. Georgakakis
  • J. Huang
  • J. Lotz
  • K. Nandra
  • J. Newman
  • C. Papovich
  • B. Weiner
  • C. Willmer
چکیده

We present the results of a study on the properties and evolution of massive (M∗ > 10 11 M⊙ ) galaxies at z ∼ 0.4 − 2 utilising 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 to a 5 σ depth of Ks,vega ∼ 20.5. Our primary goal is obtaining a broad census of massive galaxies through measuring how their number and mass densities, morphology, as well as their star formation and AGN content evolve from z ∼ 0.4− 2. Our major findings include: (i) statistically the mass and number densities of M∗ > 10 11 M⊙ galaxies show little evolution between z = 0−1, and from z ∼ 0−2 for M∗ > 10 11.5 M⊙ galaxies. We however find significant evolution between 1 < z < 1.5 for 10 M⊙ < M∗ < 10 11.5 M⊙ galaxies. (ii) After examining the structures of our galaxies using Hubble ACS imaging, we find that M∗ > 10 M⊙ selected galaxies show a nearly constant elliptical fraction of ∼ 70−90% 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 (∼ 25%) of these early-types contain minor structural anomalies. (iii) We find that only a fraction (∼ 60%) of massive galaxies with M∗ > 10 11 M⊙ are on the red-sequence at z ∼ 1.4, while nearly 100% evolve onto it by z ∼ 0.4. (iv) By utilising Spitzer MIPS imaging and [OII] line fluxes we argue that M∗ > 10 11.5 M⊙ galaxies have a steeply declining star formation rate density ∼ (1+z). 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⊙ galaxies undergo on average 0.9 −0.5 major mergers at 0.4 < z < 1.4. (v) We find that a high (5%) fraction of all M∗ > 10 11 M⊙ galaxies are X-ray emitters. Roughly half of these are morphologically distorted ellipticals or peculiars. Finally, we compare our mass growth with semianalytical models from the Millennium simulation, finding relative good agreement at z < 2 for the M∗ < 10 11.5 M⊙ systems, but that the number and mass densities of M∗ > 10 11.5 M⊙ galaxies are under predicted by a factor of > 100.

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تاریخ انتشار 2008