Revealing the Nature of a Lyman-$\alpha$ Halo in a Strongly Lensed Interacting System at $z=2.92$

TL;DR

This study uses high-resolution spectroscopic observations of a strongly-lensed galaxy pair at z=2.92 to analyze the structure, kinematics, and potential powering mechanisms of an extended Ly$ extalpha$ halo, revealing outflows and satellite contributions.

Contribution

It provides the first detailed kinematic analysis of a Ly$ extalpha$ halo in a strongly-lensed system at high redshift using radiative transfer models and identifies satellite galaxies influencing the halo.

Findings

Mean outflow velocity of approximately 211 km/s.

Detection of a faint satellite galaxy contributing to the Ly$ extalpha$ emission.

Variation in Ly$ extalpha$ line profile across the halo.

Abstract

Spatially extended halos of H I Ly$\alpha$ 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$\alpha$ 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$\alpha$ halo of $L_{Ly\alpha}=(6.2\pm1.3)\times10^{42}$ 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$\alpha$ spectra with a collection of radiative transfer galactic wind models, we infer a mean outflow expansion velocity of $\approx 211$ 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 ($M_{1500} \approx -16.7$) companion detected in both Ly$\alpha$ and the continuum, whose properties are in agreement with a predicted population of satellite galaxies that contribute to the extended Ly$\alpha$ 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$\alpha$ production.