Revealing the Nature of a Lyα Halo in a Strongly Lensed Interacting System at z = 2.92

Abstract

Spatially extended halos of H i Ly α emission are now ubiquitously found around high-redshift star-forming galaxies. But our understanding of the nature and powering mechanisms of these halos is still hampered by the complex radiative transfer effects of the Ly α line and limited angular resolution. In this paper, we present resolved Multi Unit Spectroscopic Explorer (MUSE) observations of SGAS J122651.3+215220, a strongly lensed pair of L * galaxies at z = 2.92 embedded in a Ly α halo of L Ly α = (6.2 ± 1.3) × 10 42 erg s −1 . Globally, the system shows a line profile that is markedly asymmetric and redshifted, but its width and peak shift vary significantly across the halo. By fitting the spatially binned Ly α spectra with a collection of radiative transfer galactic wind models, we infer a mean outflow expansion velocity of ≈211 km s −1 , with higher values preferentially found on both sides of the system’s major axis. The velocity of the outflow is validated with the blueshift of low-ionization metal absorption lines in the spectra of the central galaxies. We also identify a faint ( M 1500 ≈ −16.7) companion detected in both Ly α and the continuum, whose properties are in agreement with a predicted population of satellite galaxies that contribute to the extended Ly α emission. Finally, we briefly discuss the impact of the interaction between the central galaxies on the properties of the halo and the possibility of in situ fluorescent Ly α production.