COALAS

I. ATCA CO(1–0) survey and luminosity function in the Spiderweb protocluster at z = 2.16

¹ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
e-mail: shuowen.jin@gmail.com
² Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁵ International Centre for Radio Astronomy Research (ICRAR), M468, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁷ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
⁸ The University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁹ Astronomy Unit, Department of Physics, University of Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹⁰ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹¹ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
¹² Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis Blvd Arago, 75014 Paris, France
¹³ Sub-dept of Astrophysics, Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹⁴ Department of Astronomy, The University of Texas at Austin, 2515 Speedway Blvd Stop C1400, Austin, TX 78712, USA
¹⁵ CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
¹⁶ Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
¹⁷ International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
¹⁸ Subaru Telescope, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 650 North A’ohoku Place, Hilo, HI 96720, USA
¹⁹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
²⁰ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
²¹ Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
²² Leiden Observatory, PO Box 9513 2300 RA Leiden, The Netherlands
²³ Observatório Nacional, Rua General José Cristino, 77, Sao Cristóvao, Rio de Janeiro, RJ 20921-400, Brazil
²⁴ Instituto de Radioastronomía Milimétrica, Av. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
²⁵ University Vienna, Department of Astrophysics, Türkenschanzstraße 17, 1180 Wien, Austria

Received: 24 December 2020
Accepted: 15 March 2021

Abstract

We report a detailed CO(1−0) survey of a galaxy protocluster field at z = 2.16, based on 475 h of observations with the Australia Telescope Compact Array. We constructed a large mosaic of 13 individual pointings, covering an area of 21 arcmin² and ±6500 km s⁻¹ range in velocity. We obtained a robust sample of 46 CO(1−0) detections spanning z = 2.09 − 2.22, constituting the largest sample of molecular gas measurements in protoclusters to date. The CO emitters show an overdensity at z = 2.12 − 2.21, suggesting a galaxy super-protocluster or a protocluster connected to large-scale filaments of ∼120 cMpc in size. We find that 90% of CO emitters have distances >0.′5−4′ to the center galaxy, indicating that small area surveys would miss the majority of gas reservoirs in similar structures. Half of the CO emitters have velocities larger than escape velocities, which appears gravitationally unbound to the cluster core. These unbound sources are barely found within the R₂₀₀ radius around the center, which is consistent with a picture in which the cluster core is collapsed while outer regions are still in formation. Compared to other protoclusters, this structure contains a relatively higher number of CO emitters with relatively narrow line widths and high luminosities, indicating galaxy mergers. We used these CO emitters to place the first constraint on the CO luminosity function and molecular gas density in an overdense environment. The amplitude of the CO luminosity function is 1.6 ± 0.5 orders of magnitude higher than that observed for field galaxy samples at z ∼ 2, and one order of magnitude higher than predictions for galaxy protoclusters from semi-analytical SHARK models. We derive a high molecular gas density of 0.6 − 1.3 × 10⁹ M_⊙ cMpc⁻³ for this structure, which is consistent with predictions for cold gas density of massive structures from hydro-dynamical DIANOGA simulations.