(Re)Solving Reionization with Lyα : How Bright Lyα Emitters account for the $z\approx2-8$ Cosmic Ionizing Background

Matthee, Jorryt and Naidu, Rohan P. and Pezzulli, Gabriele and Gronke, Max and Sobral, David and Oesch, Pascal A. and Hayes, Matthew and Erb, Dawn and Schaerer, Daniel and Amorín, Ricardo and Tacchella, Sandro and Paulino-Afonso, Ana and Llerena, Mario and Calhau, João and Röttgering, Huub (2022) (Re)Solving Reionization with Lyα : How Bright Lyα Emitters account for the $z\approx2-8$ Cosmic Ionizing Background. Monthly Notices of the Royal Astronomical Society, 512 (4). 5960–5977. ISSN 0035-8711

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The cosmic ionizing emissivity from star-forming galaxies has long been anchored to UV luminosity functions. Here we introduce an emissivity framework based on Ly$\alpha$ emitters (LAEs), which naturally hones in on the subset of galaxies responsible for the ionizing background due to the intimate connection between the production and escape of Ly$\alpha$ and LyC photons. Using constraints on the escape fractions of bright LAEs ($L_{\rm{Ly\alpha}}>0.2 L^{*}$) at $z\approx2$ obtained from resolved Ly$\alpha$ profiles, and arguing for their redshift-invariance, we show that: (i) quasars and LAEs together reproduce the relatively flat emissivity at $z\approx2-6$, which is non-trivial given the strong evolution in both the star-formation density and quasar number density at these epochs and (ii) LAEs produce late and rapid reionization between $z\approx6-9$ under plausible assumptions. Within this framework, the $>10\times$ rise in the UV population-averaged $f_{\rm{esc}}$ between $z\approx3-7$ naturally arises due to the same phenomena that drive the growing Ly$\alpha$ emitter fraction with redshift. Generally, a LAE dominated emissivity yields a peak in the distribution of the ionizing budget with UV luminosity as reported in latest simulations. Using our adopted parameters ($f_{\rm{esc}}=50\%$, $\xi_{\rm{ion}}=10^{25.9}$ Hz erg$^{-1}$ for half the bright LAEs), we find that a highly ionizing minority of galaxies with $M_{\rm UV}5$. We conclude with proposed observational tests to further develop our suggested Ly$\alpha$-anchored formalism.

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Journal Article
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Monthly Notices of the Royal Astronomical Society
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This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The definitive publisher-authenticated version Jorryt Matthee, Rohan P Naidu, Gabriele Pezzulli, Max Gronke, David Sobral, Pascal A Oesch, Matthew Hayes, Dawn Erb, Daniel Schaerer, Ricardo Amorín, Sandro Tacchella, Ana Paulino-Afonso, Mario Llerena, João Calhau, Huub Röttgering, (Re)Solving reionization with Lyα: how bright Lyα Emitters account for the z ≈ 2–8 cosmic ionizing background, Monthly Notices of the Royal Astronomical Society, Volume 512, Issue 4, June 2022, Pages 5960–5977 is available online at: https://academic.oup.com/mnras/article/512/4/5960/6553844
Uncontrolled Keywords:
?? galaxies: high-redshiftintergalactic mediumcosmology: observationsdark agesreionizationfirst starsultraviolet: galaxiesastronomy and astrophysicsspace and planetary science ??
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22 Mar 2022 10:30
Last Modified:
27 Apr 2024 06:40