Two modes of LyC escape from bursty star formation: implications for [C II] deficits and the sources of reionization

Journal article

We use the SPHINX²⁰ cosmological radiation hydrodynamics simulation to study how Lyman continuum (LyC) photons escape from galaxies and the observational signatures of this escape. We define two classes of LyC leaker: Bursty Leakers and Remnant Leakers, based on their star formation rates (SFRs) that are averaged over 10 Myr (SFR₁₀) or 100 Myr (SFR₁₀₀). Both have f_esc>20 per cent and experienced an extreme burst of star formation, but Bursty Leakers have SFR₁₀ > SFR₁₀₀, while Remnant Leakers have SFR₁₀ < SFR₁₀₀. The maximum SFRs in these bursts were typically ∼100 times greater than the SFR of the galaxy prior to the burst, a rare 2σ outlier among the general high-redshift galaxy population. Bursty Leakers are qualitatively similar to ionization-bounded nebulae with holes, exhibiting high ionization parameters and typical H II region gas densities. Remnant Leakers show properties of density-bounded nebulae, having normal ionization parameters but much lower H II region densities. Both types of leaker exhibit [C II]_158μm deficits on the [C II]–SFR₁₀₀ relation, while only Bursty Leakers show deficits when ₁₀ is used. We predict that [C II] luminosity and SFR indicators such as Hα and M_1500Å can be combined to identify both types of LyC leaker and the mode by which photons are escaping. These predictions can be tested with [C II] observations of known z = 3–4 LyC leakers. Finally, we show that leakers with f_esc>20 per cent dominate the ionizing photon budget at z ≳ 7.5 but the contribution from galaxies with f_esc<5 per cent becomes significant at the tail-end of reionization.

Authors: Katz, H; Saxena, A; Rosdahl, J; Kimm, T; Blaizot, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 518
• Issue: 1
• Pages: 270-285
• Publication date: 2022-10-21
• Acceptance date: 2022-10-14
• DOI: 10.1093/mnras/stac3019
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: ISM: evolution; galaxies: high-redshift; ISM: general; galaxies: formation; stars: formation; galaxies: evolution; FFR