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We thank an anonymous referee for valuable comments that have greatly improved the paper. This paper makes use of the following ALMA data: ADS/JAO. ALMA #2015.1.00594S and #2018.1.01332. S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/ gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/ dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. T.H. was Researchers, MEXT, Japan (HJH02007) and by JSPS KAKENHI grant No. 22H01258. A.K.I., Y.S., and Y.F. are supported by NAOJ ALMA Scientific Research grant No. 2020- 16B. A.K.I. also acknowledges funding from JSPS KAKENHI grant No. 23H00131. Y.T. is supported by JSPS KAKENHI grant No. 22H04939. K.M. acknowledges financial support from the Japan Society for the Promotion of Science (JSPS) through KAKENHI grant No. 20K14516. J. A.-M., L.C., A.C-G., and C. B.-P. acknowledge support by grant PIB2021-127718NB-100 from the Spanish Ministry of Science and Innovation/State Agency of Research MCIN/ AEI/10.13039/501100011033 and by "ERDF A way of making Europe". C.B.-P. acknowledges support by grant CM21_CAB_M2_01 from the Program " Garantia Juvenil" from the " Comunidad de Madrid" 2021. L.C. acknowledges financial support from Comunidad de Madrid under Atraccion de Talento grant 2018-T2/TIC-11612. M.P.S. acknowledges funding support from the Ramon y Cajal program of the Spanish Ministerio de Ciencia e Innovacion (RYC2021033094-I). We are grateful to Takahiro Morishita, Nicolas Laporte, Guido Roberts-Borsani, Seiji Fujimoto, and Hide Yajima for useful discussion.

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Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): the core of the Highest-redshift Galaxy Overdensity at z=7.88 confirmed by NIRSpec/JWST

Publicated to:Astrophysical Journal Letters. 955 (1): L2- - 2023-09-01 955(1), DOI: 10.3847/2041-8213/acf57c

Authors: Hashimoto, T; Álvarez-Márquez, J; Fudamoto, Y; Colina, L; Inoue, AK; Nakazato, Y; Ceverino, D; Yoshida, N; Costantin, L; Sugahara, Y; Gómez, AC; Blanco-Prieto, C; Mawatari, K; Arribas, S; Marques-Chaves, R; Pereira-Santaella, M; Bakx, TJLC; Hagimoto, M; Hashigaya, T; Matsuo, H; Tamura, Y; Usui, M; Ren, YW

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Abstract

The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O III] 4960 and 5008 angstrom in a small area of similar to 3 '' x 3 '', corresponding to similar to 11 x 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, beta similar to -1.3. The member galaxies have stellar masses in the range of log(M-*/M-circle dot) similar to 7.6-9.2 and star formation rates of similar to 3-50 M-circle dot yr(-1), showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [O III] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with M-* similar to 6 x 10(9)M(circle dot). The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.

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