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

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 {approx} 1.6 field galaxies with M{sub star} {>=} 3 Multiplication-Sign 10{sup 10} M{sub Sun }, 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 {sup +13}{sub -14}% of all M{sub star} {>=} 3 Multiplication-Sign 10{sup 10} M{sub Sun} 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 {approx}3-10 times higher than the merger rate of massive field galaxies at z {approx} 1.6. Close pairs in the cluster have minor merger stellar mass ratios (M{sub primary}: M{sub satellite} {>=} 4), while the field pairs consist of both major and minor mergers. At least half of themore » cluster mergers are gas-poor, as indicated by their red colors and low 24 {mu}m fluxes. Two of the double-nucleated cluster members have X-ray detected active galactic nuclei with L{sub x} > 10{sup 43} erg s{sup -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.« less
Authors:
; ; ;  [1] ; ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  2. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A and M University, College Station, TX (United States)
  3. UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA (United States)
  4. Department of Physics and Astronomy, University of Kentucky, Lexington, KY (United States)
  5. Department of Physics, Purdue University, West Lafayette, IN (United States)
  6. Department of Physics and Astronomy, University of Missouri-Kansas City, 5110 Rockhill Road, Kansas City, MO (United States)
  7. Department of Astronomy, Yale University, New Haven, CT (United States)
  8. Department of Physics and Astronomy, University of Kansas, Lawrence, KS (United States)
  9. Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching (Germany)
  10. Max-Planck-Institut fuer Astronomie, D-69117 Heidelberg (Germany)
  11. Steward Observatory, University of Arizona, Tucson, AZ (United States)
Publication Date:
OSTI Identifier:
22130975
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 773; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; COLOR; GALACTIC EVOLUTION; GALAXY CLUSTERS; GALAXY NUCLEI; MASS; RANDOMNESS; RED SHIFT; TELESCOPES; X RADIATION