Abstract
Identifying low-redshift galaxies that emit Lyman Continuum radiation (LyC
leakers) is one of the primary, indirect methods of studying galaxy formation
in the epoch of reionization. However, not only has it proved challenging to
identify such systems, but it also remains uncertain whether the low-redshift
LyC leakers are true änalogues" of the sources that reionized the Universe.
Here, we use high-resolution cosmological radiation hydrodynamics simulations
to examine whether simulated galaxies in the epoch of reionization share
similar emission-line properties to observed LyC leakers at $z\sim3$ and
$z\sim0$. We find that the simulated galaxies with high LyC escape fractions
($f_esc$) often exhibit high O32 and populate the same regions of the
R23-O32 plane as $z\sim3$ LyC leakers. However, we show that viewing angle,
metallicity, and ionisation parameter can all impact where a galaxy resides on
the O32-$f_esc$ plane. Based on emission line diagnostics and how they
correlate with $f_esc$, lower-metallicity LyC leakers at $z\sim3$ appear
to be good analogues of reionization-era galaxies. In contrast, we find that
identifying low-redshift galaxies based on SII deficiencies does not seem to
produce true analogues. We use our simulated galaxies to develop multiple new
diagnostics to identify LyC leakers using IR and nebular emission lines. We
show that our model using only CII$_158m$ and OIII$_88\mu
m$ can identify potential leakers from non-leakers from the local Dwarf Galaxy
Survey. Finally, we apply this diagnostic to known high-redshift galaxies and
find that MACS1149\_JD1 at $z=9.1$ is the most likely galaxy to be actively
contributing to the reionization of the Universe.
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