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

Abstract

Hydrogen Ly$\hat{I}\pm$ 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$\hat{I}\pm$ haloes around individual UV-selected galaxies, rather than around Ly$\hat{I}\pm$ 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-hour) 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 Ly$\hat{I}\pm$ 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$\hat{I}\pm$ emission around non-LAEs. The Ly$\hat{I}\pm$ 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$\hat{I}\pm$ emission extends to 5.4 arcsec (~40 physical kpc at the midpoint redshift z=3.6) above the typical 1$\ddot{I}ƒ$ SB limit. The incidence rate of surrounding gas detected in Ly$\hat{I}\pm$ 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 Ly$\hat{I}\pm$ emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Ly$\hat{I}\pm$ systems (DLAs) and sub-DLAs.

33 pages, 13 + 10 figures, 3 tables, published in A&A, Table 1 updated after the acceptance based on a new version of the MUSE catalog