A gravitationally-boosted MUSE survey for emission-line galaxies at z>~5 behind the massive cluster RCS 0224

Abstract

We present a VLT/MUSE survey of lensed high-redshift galaxies behind the z=0.77 cluster RCS0224-0002. We study the detailed internal properties of a highly magnified (μ~29) z=4.88 galaxy seen through the cluster. We detect wide-spread nebular CIVλλ1548,1551à emission from this galaxy as well as a bright Lyα halo with a spatially-uniform wind and absorption profile across 12 kpc in the image plane. Blueshifted high- and low-ionisation interstellar absorption indicate the presence of a high-velocity outflow (Δv~300 km/s) from the galaxy. Unlike similar observations of galaxies at z=2-3, the Lyα emission from the halo emerges close to the systemic velocity - an order of magnitude lower in velocity offset than predicted in "shell"-like outflow models. To explain these observations we favour a model of an outflow with a strong velocity gradient, which changes the effective column density seen by the Lyα photons. We also search for high-redshift Lyα emitters and identify 14 candidates between z=4.8-6.6, including an over-density at z=4.88, of which only one has a detected counterpart in HST/ACS+WFC3 imaging.

21 pages, 16 figures, MNRAS, in press