CAUGHT IN THE ACT: THE ASSEMBLY OF MASSIVE CLUSTER GALAXIES AT z=1.62 uri icon

abstract

  • We present the recent merger history of massive galaxies in a spectroscopically confirmed proto-cluster at z = 1.62. Using Hubble Space Telescope WFC3 near-infrared imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we select cluster and z 1.6 field galaxies with M star 3 1010 M , to determine the frequency of double nuclei or close companions within projected separations less than 20 kpc co-moving. We find that four out of five spectroscopically confirmed massive proto-cluster galaxies have double nuclei, and 57 % of all M star 3 1010 M cluster candidates are observed in either close pair systems or have double nuclei. In contrast, only 11% 3% of the field galaxies are observed in close pair/double nuclei systems. After correcting for the contribution from random projections, the implied merger rate per massive galaxy in the proto-cluster is 3-10 times higher than the merger rate of massive field galaxies at z 1.6. Close pairs in the cluster have minor merger stellar mass ratios (M primary: M satellite 4), while the field pairs consist of both major and minor mergers. At least half of the cluster mergers are gas-poor, as indicated by their red colors and low 24 m fluxes. Two of the double-nucleated cluster members have X-ray detected active galactic nuclei with Lx > 1043 erg s-1, and are strong candidates for dual or offset super-massive black holes. We conclude that the massive z = 1.62 proto-cluster galaxies are undergoing accelerated assembly via minor mergers, and discuss the implications for galaxy evolution in proto-cluster environments. 2013. The American Astronomical Society. All rights reserved.

published proceedings

  • ASTROPHYSICAL JOURNAL

altmetric score

  • 2.35

author list (cited authors)

  • Lotz, J. M., Papovich, C., Faber, S. M., Ferguson, H. C., Grogin, N., Guo, Y., ... Willmer, C.

citation count

  • 61

complete list of authors

  • Lotz, Jennifer M||Papovich, Casey||Faber, SM||Ferguson, Henry C||Grogin, Norman||Guo, Yicheng||Kocevski, Dale||Koekemoer, Anton M||Lee, Kyoung-Soo||McIntosh, Daniel||Momcheva, Ivelina||Rudnick, Gregory||Saintonge, Amelie||Tran, Kim-Vy||van der Wel, Arjen||Willmer, Christopher

publication date

  • August 2013