Three Lyman-α-emitting filaments converging to a massive galaxy group at z = 2.91: discussing the case for cold gas infall

¹ CEA, Irfu, DAp, AIM, Université Paris-Saclay, Université de Paris, CNRS, 91191 Gif-sur-Yvette, France
e-mail: edaddi@cea.fr
² Cosmic Dawn Center (DAWN), Copenhagen, Denmark
³ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
⁴ Department of Physics & Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA
⁵ California Institute of Technology, 1216 East California Boulevard, Pasadena, CA, 91125 USA
⁶ Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, 21218, USA
⁷ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, 00014 Helsinki, Finland
⁸ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
⁹ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano; Via E. Bianchi 46, 23807 Merate, Italy
¹⁰ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
¹¹ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹² Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany
¹³ Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 Munich, Germany
¹⁴ Dipartimento di Fisica, Universitá di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
¹⁵ INAF-Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
¹⁶ INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
¹⁷ Max-Planck-Institut fur Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany
¹⁸ Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla, 4059 Valparaiso, Chile
¹⁹ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
²⁰ Centre for Extragalactic Astronomy, Durham University, South Road, Durham, DH1 3LE, UK
²¹ Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

Received: 19 June 2020
Accepted: 22 February 2021

Abstract

We have discovered a 300 kpc-wide giant Lyman-α (Lyα) nebula centered on the massive galaxy group RO-1001 at z = 2.91 in the Cosmic Evolution Survey field. Keck Cosmic Web Imager observations reveal three cold gas filaments converging into the center of the potential well of its ∼4 × 10¹³ M_⊙ dark matter halo, hosting 1200 M_⊙ yr⁻¹ of star formation as probed by Atacama Large Millimeter Array and NOrthern Extended Millimeter Array observations. The nebula morphological and kinematics properties and the prevalence of blueshifted components in the Lyα spectra are consistent with a scenario of gas accretion. The upper limits on active galactic nuclei activity and overall energetics favor gravity as the primary Lyα powering source and infall as the main source of gas flows to the system. Although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift.