Extended Lyman α haloes around individual high-redshift galaxies revealed by MUSE

摘要

We report the detection of extended Ly α emission around individual star-forming galaxies at redshifts z = 3?6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness ( 1 σ ) of ~1 × 10~(-19) erg s ~(-1) cm ~(-2) arcsec ~(-2) in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Ly α -emitting, but mostly continuum-faint ( m _(AB) ? 27 ) galaxies. In most objects the Ly α emission is considerably more extended than the UV continuum light. While five of the faintest galaxies in the sample show no significantly detected Ly α haloes, the derived upper limits suggest that this is due to insufficient S/N. Ly α haloes therefore appear to be ubiquitous even for low-mass ( ~ 10~(8)?10~(9) M _(⊙) ) star-forming galaxies at z & 3 . We decompose the Ly α emission of each object into a compact component tracing the UV continuum and an extended halo component, and infer sizes and luminosities of the haloes. The extended Ly α emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5 ? 15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor ~ 5, than Ly α haloes around low-redshift star-forming galaxies. Between ~ 40% and ? 90% of the observed Ly α flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Ly α halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z & 3 .