DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2.506
- Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu, CNRS, Université Paris Diderot, Saclay, pt courrier 131, F-91191 Gif-sur-Yvette (France)
- Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-0014 Helsinki (Finland)
- Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008 (China)
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
- European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago (Chile)
- Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, D-81679 München (Germany)
- School of Physics, Korea Institute for Advanced Study, Hoegiro 85, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)
- Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom)
- Department of Physics, Anhui Normal University, Wuhu, Anhui, 241000 (China)
- Department of Astronomy, Yale University, New Haven, CT 06511 (United States)
- Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z {sub spec} = 2.506, which contains 11 massive (M {sub *} ≳ 10{sup 11} M {sub ⊙}) galaxies in the central 80 kpc region (11.6 σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from H α . The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M {sub 200} {sub c} = 10{sup 13.9±0.2} M {sub ⊙}, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ∼3400 M {sub ⊙} yr{sup −1} with a gas depletion time of ∼200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (∼25%, compared to 3%–5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.
- OSTI ID:
- 22667462
- Journal Information:
- Astrophysical Journal, Vol. 828, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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