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

Matthee, Jorryt and Sobral, David and Gronke, Max and Pezzulli, Gabriele and Cantalupo, Sebastiano and Röttgering, Huub and Darvish, Behnam and Santos, Sérgio (2020) Resolved Lyman-α properties of a luminous Lyman-break galaxy in a large ionised bubble at z = 6.53. Monthly Notices of the Royal Astronomical Society, 492 (2). pp. 1778-1790. ISSN 0035-8711

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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$_0=38$ A). These data are combined with deep resolved [CII]$_{\rm 158 \mu m}$ spectroscopy obtained with ALMA and UV imaging from HST. Ly$\alpha$ emission is clearly detected with S/N $\approx40$ and FWHM of 370 km s$^{-1}$. We also detect UV continuum with MUSE. Ly$\alpha$ and [CII] are similarly extended beyond the UV, with effective radius r$_{\rm eff} = 2.1\pm0.2$ kpc for a single component or r$_{\rm eff, Ly\alpha, halo} = 3.45^{+1.08}_{-0.87}$ kpc when measured jointly with the UV continuum. The Ly$\alpha$ profile is broader and redshifted with respect to the [CII] line (by 220 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, while spatially varying HI column densities are also present. 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.