COALAS

III. The ATCA CO(1–0) look at the growth and death of Hα emitters in the Spiderweb protocluster at z = 2.16

¹ Instituto de Astrofísica de Canarias (IAC), E-38205 La Laguna, Tenerife, Spain
² Universidad de La Laguna, Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain
³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁴ First Light Fusion Ltd., Unit 9/10 Oxford Pioneer Park, Mead Road, Yarnton, Kidlington OX5 1QU, UK
⁵ Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85719, USA
⁶ Australia Telescope National Facility, CSIRO Space and Astronomy, PO Box 76 Epping, NSW 1710, Australia
⁷ Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
⁸ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius, (CA), Italy
⁹ International Centre for Radio Astronomy Research, Curtin University, 1 Turner Avenue, Bentley, WA 6102, Australia
¹⁰ Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹¹ Department of Astronomy, The University of Texas at Austin, 2515 Speedway Blvd Stop C1400, Austin, TX 78712, USA
¹² School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China
¹³ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210093, China
¹⁴ Astronomical Institute, Tohoku University, 6-3, Aramaki, Aoba, Sendai, Miyagi 980-8578, Japan
¹⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, D-85748 Garching bei München, Germany
¹⁶ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹⁷ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
¹⁸ DTU Space, Technical University of Denmark, Elektrovej 327, DK2800 Kgs. Lyngby, Denmark
¹⁹ Dept. of Astronomical Science, The Graduate University for Advanced Studies, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁰ Subaru Telescope, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 650 North A’ohoku Place, Hilo, HI 96720, USA
²¹ Centre de Recherche Astrophysique de Lyon, ENS de Lyon, Université Lyon 1, CNRS, UMR5574, F-69230 Saint-Genis-Laval, France
²² Leiden Observatory, Leiden University, PO Box 9513 NL-2300 RA Leiden, The Netherlands
²³ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁴ Instituto de Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Núcleo Central, E-18012 Granada, Spain
²⁵ Waseda Institute for Advanced Study (WIAS), Waseda University, 1-21-1 Nishi-Waseda, Shinjuku, Tokyo 169-0051, Japan
²⁶ Center for Data Science, Waseda University, 1-6-1 Nishi-Waseda, Shinjuku, Tokyo 169-0051, Japan
²⁷ Purple Mountain Observatory, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing 210023, China
²⁸ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, Anhui 230026, China
²⁹ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria

^⋆ Corresponding author: jm.perez@iac.es

Received: 18 May 2024
Accepted: 3 January 2025

Abstract

We obtain CO(1−0) molecular gas measurements with the Australia Telescope Compact Array on a sample of 43 spectroscopically confirmed Hα emitters in the Spiderweb protocluster at z = 2.16 and investigate the relation between their star formation activities and cold gas reservoirs as a function of environment. We achieve a CO(1−0) detection rate of ∼23 ± 12% with ten dual CO(1−0) and Hα detections within our sample at 10 < log M_*/M_⊙ < 11.5. In addition, we obtain upper limits for the remaining sources. In terms of total gas fractions (F_gas), we find our sample is divided into two different regimes mediated by a steep transition at log M_*/M_⊙ ≈ 10.5. Galaxies below that threshold have gas fractions that in some cases are close to unity, indicating that their gas reservoir has been replenished by inflows from the cosmic web. However, objects at log M_*/M_⊙ > 10.5 display significantly lower gas fractions than their lower stellar mass counterparts and are dominated (12 out of 20) by objects hosting an active galactic nucleus (AGN). Stacking results yield F_gas ≈ 0.55 for massive emitters excluding AGN, and F_gas ≈ 0.35 when examining only AGN candidates. Furthermore, depletion times of our sample show that most Hα emitters at z = 2.16 will become passive by 1 < z < 1.6, concurrently with the surge and dominance of the red sequence in the most massive clusters. Our environmental analyses suggest that galaxies residing in the outskirts of the protocluster have larger molecular-to-stellar mass ratios and lower star formation efficiencies than galaxies residing in the core. However, star formation across the protocluster structure remains consistent with the main sequence, indicating that galaxy evolution is primarily driven by the depletion of the gas reservoir towards the inner regions. We discuss the relative importance of inflow and outflow processes in regulating star formation during the early phases of cluster assembly and conclude that a combination of feedback and overconsumption may be responsible for the rapid cold gas depletion these objects endure.