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  • 2110.11961v1

    Rights statement: 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 Rohan P Naidu, Jorryt Matthee, Pascal A Oesch, Charlie Conroy, David Sobral, Gabriele Pezzulli, Matthew Hayes, Dawn Erb, Ricardo Amorín, Max Gronke, Daniel Schaerer, Sandro Tacchella, Josephine Kerutt, Ana Paulino-Afonso, João Calhau, Mario Llerena, Huub Röttgering, The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50, Monthly Notices of the Royal Astronomical Society, 2022 510, 3: 4582-4607 is available online at: https://academic.oup.com/mnras/article/510/3/4582/6459744

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The Synchrony of Production & Escape: Half the Bright Ly$α$ Emitters at $z\approx2$ have Lyman Continuum Escape Fractions $\approx50\%$

Research output: Contribution to journalJournal articlepeer-review

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  • Rohan P. Naidu
  • Jorryt Matthee
  • Pascal A. Oesch
  • Charlie Conroy
  • David Sobral
  • Gabriele Pezzulli
  • Matthew Hayes
  • Dawn Erb
  • Ricardo Amorín
  • Max Gronke
  • Daniel Schaerer
  • Sandro Tacchella
  • Josephine Kerutt
  • Ana Paulino-Afonso
  • João Calhau
  • Mario Llerena
  • Huub Röttgering
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<mark>Journal publication date</mark>31/03/2022
<mark>Journal</mark>Monthly Notices of the Royal Astronomical Society
Issue number3
Volume510
Number of pages26
Pages (from-to)4582-4607
Publication StatusPublished
Early online date11/12/21
<mark>Original language</mark>English

Abstract

The ionizing photon escape fraction (LyC $f_{\rm{esc}}$) of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshift. Here we circumvent this uncertainty by inferring $f_{\rm{esc}}$ with resolved (R>4000) LyA profiles from the X-SHOOTER LyA survey at z=2 (XLS-z2). We select leakers ($f_{\rm{esc}}>20$%) and non-leakers ($f_{\rm{esc}}0.2 L^{*}$ LyA emitters (LAEs). With median stacked spectra of these subsets covering 1000-8000 {\AA} (rest-frame) we investigate the conditions for LyC $f_{\rm{esc}}$. We find the following differences between leakers vs. non-leakers: (i) strong nebular CIV and HeII emission vs. non-detections, (ii) O32~8.5 vs. ~3, (iii) Ha/Hb indicating no dust vs. E(B-V)~0.3, (iv) MgII emission close to the systemic velocity vs. redshifted, optically thick MgII, (v) LyA $f_{\rm{esc}}$ of ~50% vs. ~10%. The extreme EWs in leakers (O3+Hb~1100 {\AA}) constrain the characteristic timescale of LyC escape to ~3-10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers -- extremely ionizing stellar populations, low column densities, a dust-free, high ionization state ISM -- occur simultaneously in the $f_{\rm{esc}}>20\%$ stack, suggesting they are causally connected, and motivating why indicators like O32 may suffice to constrain $f_{\rm{esc}}$ at z>6 with JWST. The leakers comprise half our sample, have a median LyC $f_{\rm{esc}}$~50%, and an ionising production efficiency $\log({\xi_{\rm{ion}}/\rm{Hz\ erg^{-1}}})$~25.9. These results show LAEs -- the type of galaxies rare at z=2, but that become the norm at higher redshift -- are highly efficient ionizers, with extreme $\xi_{\rm{ion}}$ and prolific $f_{\rm{esc}}$ occurring in sync. (ABRIDGED)

Bibliographic note

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 Rohan P Naidu, Jorryt Matthee, Pascal A Oesch, Charlie Conroy, David Sobral, Gabriele Pezzulli, Matthew Hayes, Dawn Erb, Ricardo Amorín, Max Gronke, Daniel Schaerer, Sandro Tacchella, Josephine Kerutt, Ana Paulino-Afonso, João Calhau, Mario Llerena, Huub Röttgering, The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50, Monthly Notices of the Royal Astronomical Society, 2022 510, 3: 4582-4607 is available online at: https://academic.oup.com/mnras/article/510/3/4582/6459744