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

Abstract

The observed properties of the Lyman-α (Lyα) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Lyα spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at z = 6.532 with moderate Lyα equivalent width (EW 0 = 38Å). These data are combined with deep resolved [CII] 158µm spectroscopy obtained with ALMA and UV imaging from HST. Lyα emission is clearly detected with S/N ≈ 40 and FWHM of 370 km s −1 . We also detect UV continuum with MUSE. Lyα and [CII] are similarly extended beyond the UV, with effective radius r eff = 2.1±0.2 kpc for a single component or r eff,Lyα,halo = 3.45 +1.08 −0.87 kpc when measured jointly with the UV continuum. The Lyα 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 Lyα 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 (∼ 10 kpc) neutral gas conditions that determine the observed Lyα properties in VR7 resemble the conditions in post-re-ionisation galaxies.

The nature of CR7 revealed with MUSE: a young starburst powering extended Ly α emission at z = 6.6

“…The extended Lyα emission around CR7 is clearly elongated, with an ellipticity of ≈ 0.5 meaning that the semimajor axis is roughly twice the semi-minor axis. This is in contrast to the low ellipticity of ≈ 0.15 measured in another UV luminous LAE at z = 6.5 (Matthee et al 2020). Most earlier studies of extended Lyα emission impose circular symmetry (e.g.…”

“…Compared to non-GLAO observations (e.g. Bacon et al 2017;Matthee et al 2020) we find that while the core of the PSF is very narrow, the wing is somewhat more extended (β = 2.8 in those non-GLAO data). We measure the depth of the data by placing PSF FWHM-sized apertures in 67 empty sky positions identified by eye from deep HST data (see below) and the MUSE white-light image and measuring the standard deviation in the aperture-fluxes.…”

“…Additionally, the fraction of the Lyα flux that originates from the halo component is similar to the typical halo fraction of 66 ± 20 % in LAEs at z = 3 − 5. The scale length also resembles that of the extended Lyα emission measured in another bright LAE at z = 6.5 (Matthee et al 2020).…”

“…The most likely association is the one with the smaller velocity offset as it also has a smaller spatial separation between Lyα and [CII]. Nonetheless, both these velocity offsets are relatively high compared to the velocity offset measured at the peak of Lyα which is ∆vcomponent A = +204±4 km s −1 and also compared to other galaxies at z ≈ 5 − 7 (typically ≈ +200 km s −1 ; Matthee et al 2020;Cassata et al 2020). On the other hand, these offsets are not unseen in LAEs at z ≈ 2 − 3 (e.g.…”

“…This makes the physical interpretation of a spatially unresolved Lyα spectrum difficult, making IFU observations in the rest-frame UV necessary (e.g. Matthee et al 2020). An additional advantage of integral field spectroscopy is the possibility to define a pseudo-narrowband image which width can be optimised to maximise the signalto-noise for a given target, which facilitates the detection of emission at low surface brightness.…”