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تسجيل مستخدم جديدResolved UV and [CII] structures of luminous galaxies within the epoch of reionisation
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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$_{rm [CII]}<2.2times10^7$ L$_{odot}$ implying a metallicity $Zlesssim0.07 Z_{odot}$. Intriguingly, our HST data indicates a red UV slope $beta=-1.1pm0.7$, at odds with the low dust content. VR7, which is a bright (M$_{1500}=-22.4$) galaxy with moderate color ($beta=-1.4pm0.3$) and Ly$alpha$ EW$_0 = 34$ A, is clearly detected in [CII] emission (S/N=15). VR7s 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 $Zapprox0.2 Z_{odot}$, 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 $zsim7$. 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.
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