Spectroscopic confirmation of a protocluster at z ≈ 3.786
- National Optical Astronomy Observatory, Tucson, AZ 85726 (United States)
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907 (United States)
- Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States)
- Department of Physics and Astronomy, University of California, Irvine, CA (United States)
- Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)
- Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
We present new observations of the field containing the z = 3.786 protocluster PC 217.96+32.3. We confirm that it is one of the largest known and most overdense high-redshift structures. Such structures are rare even in the largest cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image a 1.°2 × 0.°6 area (≈150 × 75 comoving Mpc) surrounding the protocluster’s core and discovered 165 candidate Lyα emitting galaxies (LAEs) and 788 candidate Lyman Break galaxies (LBGs). There are at least two overdense regions traced by the LAEs, the largest of which shows an areal overdensity in its core (i.e., within a radius of 2.5 comoving Mpc) of 14 ± 7 relative to the average LAE spatial density ( ρ-bar ) in the imaged field. Further, ρ-bar is twice that derived by other field LAE surveys. Spectroscopy with Keck/DEIMOS yielded redshifts for 164 galaxies (79 LAEs and 85 LBGs); 65 lie at a redshift of 3.785 ± 0.010. The velocity dispersion of galaxies near the core is σ = 350 ± 40 km s{sup −1}, a value robust to selection effects. The overdensities are likely to collapse into systems with present-day masses of >10{sup 15} M {sub ⊙} and >6 × 10{sup 14} M {sub ⊙}. The low velocity dispersion may suggest a dynamically young protocluster. We find a weak trend between narrow-band (Lyα) luminosity and environmental density: the Lyα luminosity is enhanced on average by 1.35× within the protocluster core. There is no evidence that the Lyα equivalent width depends on environment. These suggest that star formation and/or active galactic nucleus (AGN) activity is enhanced in the higher-density regions of the structure. PC 217.96+32.3 is a Coma cluster analog, witnessed in the process of formation.
- OSTI ID:
- 22869077
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 823; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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