The MUSE eXtremely Deep Field: Individual detections of Ly<i>α</i> haloes around rest-frame UV-selected galaxies at <i>z</i> ≃ 2.9–4.4

Abstract

Hydrogen Ly α 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 Ly α haloes around individual UV-selected galaxies, rather than around Ly α emitters (LAEs), at high redshifts. Our sample was continuum-selected with F 775 W ≤ 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 F 775 W -magnitude selected within the redshift range z ≈ 2.9 − 4.4 and within a UV magnitude range −20 ≤ M 1500 ≤ −18, thus avoiding any bias toward LAEs. We tested whether galaxy’s Ly α 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 Ly α emission around non-LAEs. The Ly α 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 Ly α emission extends to 5.4 arcsec (≃40 physical kpc at the midpoint redshift z = 3.6) above the typical 1 σ SB limit. The incidence rate of surrounding gas detected in Ly α per one-dimensional line of sight per unit redshift, d n /d z , is estimated to be 0.76 −0.09 +0.09 for galaxies with M 1500 ≤ −18 mag at z ≃ 3.7. Assuming that Ly α emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Ly α systems (DLAs) and sub-DLAs.