Resolved UV and [CII] structures of luminous galaxies within the epoch
  of reionisation
  We present new deep ALMA and HST/WFC3 observations of MASOSA and VR7, two
luminous Ly$\alpha$ emitters (LAEs) at $z=6.5$, for which the UV continuum
level differ by a factor four. No IR dust continuum emission is detected in
either, indicating little amounts of obscured star formation and/or high dust
temperatures. MASOSA, with a UV luminosity M$_{1500}=-20.9$, compact size and
very high Ly$\alpha$ EW$_{0}\approx145$ A, is undetected in [CII] to a limit of
L$_{\rm [CII]}<2.2\times10^7$ L$_{\odot}$ implying a metallicity $Z\lesssim0.07
Z_{\odot}$. Intriguingly, our HST data indicates a red UV slope
$\beta=-1.1\pm0.7$, at odds with the low dust content. VR7, which is a bright
(M$_{1500}=-22.4$) galaxy with moderate color ($\beta=-1.4\pm0.3$) and
Ly$\alpha$ EW$_0 = 34$ A, is clearly detected in [CII] emission (S/N=15). VR7's
rest-frame UV morphology can be described by two components separated by
$\approx1.5$ kpc and is globally more compact than the [CII] emission. The
global [CII]-UV ratio indicates $Z\approx0.2 Z_{\odot}$, but there are large
variations in the UV-[CII] ratio on kpc scales. We also identify diffuse,
possibly outflowing, [CII]-emitting gas at $\approx 100$ km s$^{-1}$ with
respect to the peak. VR7 appears assembling its components at a slightly more
evolved stage than other luminous LAEs, with outflows already shaping its
direct environment at $z\sim7$. Our results further indicate that the global
[CII]-UV relation steepens at SFR $<30$ M$_{\odot}$ yr$^{-1}$, naturally
explaining why the [CII]-UV ratio is anti-correlated with Ly$\alpha$ EW in
many, but not all, observed LAEs.
