Kavli Affiliate: Martin Haehnelt
| First 5 Authors: Harley Katz, Aayush Saxena, Joki Rosdahl, Taysun Kimm, Jeremy Blaizot
| Summary:
We use the SPHINX$^{20}$ 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 (SFR$_{10}$) or 100 Myr (SFR$_{100}$). Both have
$f_{rm esc}>20%$ and experienced an extreme burst of star formation, but
Bursty Leakers have ${rm SFR_{10}>SFR_{100}}$, while Remnant Leakers have
${rm SFR_{10}<SFR_{100}}$. The maximum SFRs in these bursts were typically
$sim100$ times greater than the SFR of the galaxy prior to the burst, a rare
$2sigma$ 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 HII region gas densities.
Remnant Leakers show properties of density-bounded nebulae, having normal
ionization parameters but much lower HII region densities. Both types of leaker
exhibit [CII]$_{rm 158mu m}$ deficits on the [CII]-SFR$_{100}$ relation,
while only Bursty Leakers show deficits when SFR$_{10}$ is used. We predict
that [CII] luminosity and SFR indicators such as H$alpha$ and M$_{rm
1500r{A}}$ can be combined to identify both types of LyC leaker and the mode
by which photons are escaping. These predictions can be tested with [CII]
observations of known $z=3-4$ LyC leakers. Finally, we show that leakers with
$f_{rm esc}>20%$ dominate the ionizing photon budget at $zgtrsim7.5$ but the
contribution from galaxies with $f_{rm esc}<5%$ becomes significant at the
tail-end of reionization.
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