The MUSE eXtremely Deep Field: Individual detections of Lyα haloes around rest-frame UV-selected galaxies at z ≃ 2.9–4.4^⋆

¹ Observatoire de Genève, Université de Genève, 51 chemin de Pégase, 1290 Versoix, Switzerland
e-mail: haruka.kusakabe@unige.ch
² Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
³ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁵ Department of Physics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
⁶ Department of Astronomy, University of Wisconsin, 475 N. Charter Street, Madison, WI 53706, USA
⁷ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
⁸ Aix Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13013 Marseille, France
⁹ ESO Vitacura, Alonso de Córdova 3107, Vitacura, Casilla, 19001 Santiago de Chile, Chile

Received: 24 September 2021
Accepted: 14 January 2022

Abstract

Hydrogen Lyα haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Lyα haloes around individual UV-selected galaxies, rather than around Lyα emitters (LAEs), at high redshifts. Our sample was continuum-selected with F775W ≤ 27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-h) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final sample includes 21 galaxies that are purely F775W-magnitude selected within the redshift range z ≈ 2.9 − 4.4 and within a UV magnitude range −20 ≤ M₁₅₀₀ ≤ −18, thus avoiding any bias toward LAEs. We tested whether galaxy’s Lyα emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first individual detections of extended Lyα emission around non-LAEs. The Lyα halo fraction is thus as high as 81.0_−11.2^+10.3%, which is close to that for LAEs at z = 3 − 6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Lyα emission extends to 5.4 arcsec (≃40 physical kpc at the midpoint redshift z = 3.6) above the typical 1σ SB limit. The incidence rate of surrounding gas detected in Lyα per one-dimensional line of sight per unit redshift, dn/dz, is estimated to be 0.76_−0.09^+0.09 for galaxies with M₁₅₀₀ ≤ −18 mag at z ≃ 3.7. Assuming that Lyα emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Lyα systems (DLAs) and sub-DLAs.