Resolved Lyman-α properties of a luminous Lyman-break galaxy in a large ionised bubble at z = 6.53

Abstract

The observed properties of the Lyman-$\alpha$ (Ly$\alpha$) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Ly$\alpha$ spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at $z=6.532$ with moderate Ly$\alpha$ equivalent width (EW${}_0\approx 38$ Å). These data are combined with deep resolved [CII]${}_{158\mu \mathrm{m}}$ spectroscopy obtained with ALMA and UV imaging from {\it HST} and we also detect UV continuum with MUSE. Ly$\alpha$ emission is clearly detected with S/N $\approx 40$ and FWHM of 374 km s${}^{-1}$. Ly$\alpha$ and [CII] are similarly extended beyond the UV, with effective radius r${}_{\mathrm{eff}}=2.1\pm 0.2$ kpc for a single exponential model or r${}_{\mathrm{eff},\mathrm{Ly}\alpha ,\mathrm{halo}}=3.45_{-0.87}^{+1.08}$ kpc when measured jointly with the UV continuum. The Ly$\alpha$ profile is broader and redshifted with respect to the [CII] line (by 213 km s${}^{-1}$), but there are spatial variations that are qualitatively similar in both lines and coincide with resolved UV components. This suggests that the emission originates from two components with plausibly different HI column densities. We place VR7 in the context of other galaxies at similar and lower redshift. The Ly$\alpha$ halo scale length is similar at different redshifts and velocity shifts with respect to the systemic are typically smaller. Overall, we find little indications of a more neutral vicinity at higher redshift. This means that the local ($\sim 10$ kpc) neutral gas conditions that determine the observed Ly$\alpha$ properties in VR7 resemble the conditions in post-re-ionisation galaxies.

13 pages, 10 figures. Accepted for publication in MNRAS

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