TY - JOUR
T1 - Caught in the act
T2 - The assembly of massive cluster galaxies at z = 1.62
AU - Lotz, Jennifer M.
AU - Papovich, Casey
AU - Faber, S. M.
AU - Ferguson, Henry C.
AU - Grogin, Norman
AU - Guo, Yicheng
AU - Kocevski, Dale
AU - Koekemoer, Anton M.
AU - Lee, Kyoung Soo
AU - McIntosh, Daniel
AU - Momcheva, Ivelina
AU - Rudnick, Gregory
AU - Saintonge, Amelie
AU - Tran, Kim Vy
AU - Van Der Wel, Arjen
AU - Willmer, Christopher
PY - 2013/8/20
Y1 - 2013/8/20
N2 - 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 μm 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.
AB - 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 μm 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.
KW - galaxies: clusters: general
KW - galaxies: high-redshift
KW - galaxies: interactions
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U2 - 10.1088/0004-637X/773/2/154
DO - 10.1088/0004-637X/773/2/154
M3 - Article
AN - SCOPUS:84881468429
SN - 0004-637X
VL - 773
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 154
ER -