Extended Lyman-α emission towards the SPT2349-56 protocluster at z = 4.3

¹ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
e-mail: yordanka.apostolovski@gmail.com
² Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
³ Instituto de Astrofisica, Facultad de Ciencias Exactas, Universidad Andres Bello, Fernandez Concha 700, Santiago, Chile
⁴ Millennium Institute of Astrophysics, Monseñor Nuncio Sotero Sanz 100, Oficina 104, Santiago, Chile
⁵ Aix-Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, 13388 Marseille, France
⁶ Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada
⁷ Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 4R2, Canada
⁸ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching bei München, Germany
⁹ Department of Astronomy, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL 32611, USA
¹⁰ Max Planck Institut fur Astrophysik, Karl-Schwarzschild-Straße 1, 85748 Garching bei München, Germany
¹¹ Département de Physique, Université de Montréal, Montreal, Quebec H3T 1J4, Canada
¹² Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
¹³ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green St., Urbana, IL 61801, USA
¹⁴ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA
¹⁵ Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, TX 77843-4242, USA
¹⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 23 December 2022
Accepted: 30 November 2023

Abstract

Context. Deep spectroscopic surveys with the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed that some of the brightest infrared sources in the sky correspond to concentrations of submillimeter galaxies (SMGs) at high redshift. Among these, the SPT2349-56 protocluster system is amongst the most extreme examples given its high source density and integrated star formation rate.

Aims. We conducted a deep Lyman-α line emission survey around SPT2349-56 using the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) in order to characterize this uniquely dense environment.

Methods. Taking advantage of the deep three-dimensional nature of this survey, we performed a sensitive search for Lyman-α emitters (LAEs) toward the core and northern extension of the protocluster, which correspond to the brightest infrared regions in this field. Using a smoothed narrowband image extracted from the MUSE datacube around the protocluster redshift, we searched for possible extended structures.

Results. We identify only three LAEs at z = 4.3 in this field. This number is lower than expectations for blank fields, and is significantly lower than the number of previously identified SMGs in this system. We find an extended Lyman-α structure of about 60 × 60 kpc² in size located 56 kpc east of the protocluster core. Three SMGs coincide spatially with the location of this structure. All the other SMGs are undetected in Lyman-α emission, which is consistent with the conspicuous dust obscuration in these systems. We conclude that either the three co-spatial SMGs or the protocluster core itself are feeding ionizing photons to the Lyman-α structure.