MMT spectroscopy of Lyman-alpha at z ≃ 7: evidence for accelerated reionization around massive galaxies - Faculté des Sciences de Sorbonne Université Accéder directement au contenu
Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2021

MMT spectroscopy of Lyman-alpha at z ≃ 7: evidence for accelerated reionization around massive galaxies

Ryan Endsley
Daniel Stark
  • Fonction : Auteur
Stéphane Charlot
Jacopo Chevallard
Brant Robertson
  • Fonction : Auteur
Rychard Bouwens
Mauro Stefanon

Résumé

ABSTRACT Reionization-era galaxies tend to exhibit weak Ly α emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly α emission now known in four of the most massive z = 7–9 galaxies in the CANDELS fields, all of which also exhibit intense [O iii]+H β emission (EW > 800 Å). To better understand why Ly α is anomalously strong in a subset of massive z ≃ 7–9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N = 22) of similarly luminous (≃1–6 L$^{\ast }_{\mathrm{UV}}$) z ≃ 7 galaxies selected over very wide-area fields (∼3 deg2). We confidently (>7σ) detect Ly α in 78 per cent (7/9) of galaxies with strong [O iii]+H β emission (EW > 800 Å) as opposed to only 8 per cent (1/12) of galaxies with more moderate (EW = 200–800 Å) [O iii]+H β. We argue that the higher Ly α EWs of the strong [O iii]+H β population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs (≳30 Gyr−1). We also find evidence that Ly α transmission from massive galaxies declines less rapidly over 6 < z < 7 than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly α transmission, consistent with a picture wherein massive z ≃ 7 galaxies often reside in large ionized regions. We detect three closely separated (R = 1.7 physical Mpc) z ≃ 7 Ly α emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
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hal-03381695 , version 1 (16-08-2022)

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Ryan Endsley, Daniel Stark, Stéphane Charlot, Jacopo Chevallard, Brant Robertson, et al.. MMT spectroscopy of Lyman-alpha at z ≃ 7: evidence for accelerated reionization around massive galaxies. Monthly Notices of the Royal Astronomical Society, 2021, 502 (4), pp.6044-6063. ⟨10.1093/mnras/stab432⟩. ⟨hal-03381695⟩
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