We present new deep ALMA and Hubble Space Telescope (HST)/WFC3 observations of MASOSA and VR7, two luminous Lyα emitters (LAEs) at z = 6.5, for which the UV continuum levels differ by a factor of 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 Lyα , is undetected in [C ii] to a limit of L [C ii] < 2.2 × 107 L o, implying a metallicity Z ≲ 0.07 Z o. Intriguingly, our HST data indicate a red UV slope β = -1.1 ± 0.7, at odds with the low dust content. VR7, which is a bright (M 1500 = -22.4) galaxy with moderate color (β = -1.4 ± 0.3) and Lyα EW0 = 34 Å, is clearly detected in [C ii] emission (S/N = 15). VR7's rest-frame UV morphology can be described by two components separated by ≈1.5 kpc and is globally more compact than the [C ii] emission. The global [C ii]/UV ratio indicates Z ≈ 0.2 Z o, but there are large variations in the UV/[C ii] ratio on kiloparsec scales. We also identify diffuse, possibly outflowing, [C ii]-emitting gas at ≈100 km s-1 with respect to the peak. VR7 appears to be assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at z ∼ 7. Our results further indicate that the global [C ii]-UV relation steepens at SFR < 30 M o yr-1, naturally explaining why the [C ii]/UV ratio is anticorrelated with Lyα EW in many, but not all, observed LAEs.
Resolved UV and [C ii] Structures of Luminous Galaxies within the Epoch of Reionization
Vallini L.;Ferrara A.;
2019
Abstract
We present new deep ALMA and Hubble Space Telescope (HST)/WFC3 observations of MASOSA and VR7, two luminous Lyα emitters (LAEs) at z = 6.5, for which the UV continuum levels differ by a factor of 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 Lyα , is undetected in [C ii] to a limit of L [C ii] < 2.2 × 107 L o, implying a metallicity Z ≲ 0.07 Z o. Intriguingly, our HST data indicate a red UV slope β = -1.1 ± 0.7, at odds with the low dust content. VR7, which is a bright (M 1500 = -22.4) galaxy with moderate color (β = -1.4 ± 0.3) and Lyα EW0 = 34 Å, is clearly detected in [C ii] emission (S/N = 15). VR7's rest-frame UV morphology can be described by two components separated by ≈1.5 kpc and is globally more compact than the [C ii] emission. The global [C ii]/UV ratio indicates Z ≈ 0.2 Z o, but there are large variations in the UV/[C ii] ratio on kiloparsec scales. We also identify diffuse, possibly outflowing, [C ii]-emitting gas at ≈100 km s-1 with respect to the peak. VR7 appears to be assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at z ∼ 7. Our results further indicate that the global [C ii]-UV relation steepens at SFR < 30 M o yr-1, naturally explaining why the [C ii]/UV ratio is anticorrelated with Lyα EW in many, but not all, observed LAEs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
