The VIMOS Ultra-Deep Survey: Emerging from the dark, a massive proto-cluster at z ~ 4:57

Lemaux, B. C. and Fèvre, O. Le and Cucciati, O. and Ribeiro, B. and Tasca, L. A. M. and Zamorani, G. and Ilbert, O. and Thomas, R. and Bardelli, S. and Cassata, P. and Hathi, N. P. and Pforr, J. and Smolčić, Vernesa and Delvecchio, I. and Novak, Mladen and Berta, S. and McCracken, H. J. and Koekemoer, A. and Amorín, R. and Garilli, B. and Maccagni, D. and Schaerer, D. and Zucca, E. (2018) The VIMOS Ultra-Deep Survey: Emerging from the dark, a massive proto-cluster at z ~ 4:57. Astronomy and Astrophysics, 615. A77. ISSN 0004-6361

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Using spectroscopic observations taken for the Visible Multi-Object Spectrograph (VIMOS) Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster of galaxies located at z_spec ~ 4.57 in the COSMOS field. With nine spectroscopic members, the proto-cluster was initially detected as a ~12σ spectroscopic overdensity of typical star-forming galaxies in the blind spectroscopic survey of the early universe (2 < z ≲ 6) performed by VUDS. It was further mapped using a new technique developed which statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of incredibly deep multi-band imaging performed on the COSMOS field. Through various methods, the descendant mass of PCl J1001+0220 is estimated to be log (M_h/M_⊙)_z=0 ~ 14.5–15 with a large amount of mass apparently already in place at z ~ 4.57. An exhaustive comparison was made between the properties of various spectroscopic and photometric member samples and matched samples of galaxies inhabiting less dense environments at the same redshifts. Tentative evidence is found for a fractional excess of older galaxies more massive in their stellar content amongst the member samples relative to the coeval field, an observation which suggests the pervasive early onset of vigorous star formation for proto-cluster galaxies. No evidence is found for the differences in the star formation rates (SFRs) of member and coeval field galaxies either through estimating by means of the rest-frame ultraviolet or through separately stacking extremely deep Very Large Array 3 GHz imaging for both samples. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed in either environment. Analysis of Hubble Space Telescope images of both sets of galaxies as well as their immediate surroundings provides weak evidence for an elevated incidence of galaxy–galaxy interaction within the bounds of the proto-cluster. The stacked and individual spectral properties of the two samples are compared, with a definite suppression of Lyα seen in the average member galaxy relative to the coeval field (f_esc, Lyα = 1.8_−1.7 ^+0.3% and 4.0_−0.8 ^+1.0%, respectively). This observation along with other lines of evidence leads us to infer the possible presence of a large, cool, diffuse medium within the proto-cluster environment evocative of a nascent intracluster medium forming in the early universe.

Item Type: Article
Keywords: galaxies: evolution, galaxies: clusters: general, galaxies: high-redshift, techniques: spectroscopic, techniques: photometric
Date: 2018
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © ESO 2018. Received 25 March 2017; Accepted 3 January 2018; Published online: 17 July 2018.
Divisions: Faculty of Science > Department of Physics
Publisher: EDP Sciences
Depositing User: Vernesa Smolčić
Date Deposited: 15 Apr 2019 13:59
Last Modified: 15 Apr 2019 14:06

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