The Archival Discovery of a Strong Lyα and [C ii] Emitter at z = 7.677
Francesco Valentino, Gabriel Brammer, Seiji Fujimoto, K. E. Heintz, John R. Weaver, Victoria Strait, Katriona M. L. Gould, Charlotte Mason, D. Watson, Peter Laursen, Sune Toft
Abstract
Abstract We report the archival discovery of Ly α emission from the bright ultraviolet galaxy Y002 at z = 7.677, spectroscopically confirmed by its ionized carbon [C ii ] 158 μ m emission line. The Ly α line is spatially associated with the rest-frame UV stellar emission ( M UV ∼ −22, 2× brighter than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>UV</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ), and it appears offset from the peak of the extended [C ii ] emission at the current ∼1″ spatial resolution. We derive an estimate of the unobscured SFR UV = (22 ± 1) M ⊙ yr −1 and set an upper limit of SFR IR < 15 M ⊙ yr −1 from the far-infrared (FIR) wavelength range, which globally places Y002 on the SFR(UV+IR)– L [C II ] correlation observed at lower redshifts. In terms of velocity, the peak of the Ly α emission is redshifted by Δ v Ly α ∼ 500 km s −1 from the systemic redshift set by [C ii ] and a high-velocity tail extends up to ∼1000 km s −1 . The velocity offset is up to ∼3.5× higher than the average estimate for similarly UV-bright emitters at z ∼ 6–7, which might suggest that we are witnessing the merging of two clumps. A combination of strong outflows and the possible presence of an extended ionized bubble surrounding Y002 would likely facilitate the escape of copious Ly α light, as indicated by the large equivalent width EW 0 (Ly α ) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.50em"/> <mml:mo>=</mml:mo> <mml:mspace width="0.50em"/> <mml:msubsup> <mml:mrow> <mml:mn>24</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> Å. Assuming that [C ii ] traces the neutral hydrogen, we estimate a H i gas fraction of M H I / M ⋆ ≳ 8 for Y002 as a system and speculate that patches of high H i column densities could contribute to explaining the observed spatial offsets between Ly α- and [C ii ]-emitting regions. The low dust content, implied by the nondetection of the FIR continuum emission at rest frame ∼160 μ m, would be sufficient to absorb any potential Ly α photons produced within the [C ii ] clump as a result of large H i column densities.