Abstract
In this work, we use the ASTRAEUS (semi-numerical rAdiative tranSfer coupling
of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS)
framework which couples galaxy formation and reionization in the first billion
years. Exploring a number of models for reionization feedback and the escape
fraction of ionizing radiation from the galactic environment
($f_esc$), we quantify how the contribution of star-forming galaxies
to reionization depends on the radiative feedback model, $f_esc$, and
the environmental over-density. Our key findings are: (i) for constant
$f_esc$ models, intermediate-mass galaxies (with halo masses of
$M_h\simeq10^9-11$M$_ødot$ and absolute UV magnitudes of $M_UV -15$
to $-20$) in intermediate-density regions drive reionization; (iii) scenarios
where $f_esc$ increases with decreasing halo mass shift the galaxy
population driving reionization to lower-mass galaxies
($M_h<10^9.5$M$_ødot$) with lower luminosities ($M_UV>-16$) and
over-densities; (iii) reionization imprints its topology on the ionizing
emissivity of low-mass galaxies ($M_h<10^9$M$_ødot$) through radiative
feedback. Galaxies in over-dense regions (that are reionized earlier)
experience a stronger suppression of star formation by radiative feedback and
show lower ionizing emissivities; (iv) therefore, a change in $f_esc$
with galaxy properties has the largest impact on the sources of reionization
and their detectability, with the radiative feedback strength and environmental
over-density playing a sub-dominant role; (v) JWST-surveys (with a limiting
magnitude of $M_UV = -16$) will be able to detect the galaxies providing
$\sim60\%$ ($\sim20\%$) of reionization photons at $z=7$ for constant
$f_esc$ models (scenarios where $f_esc$ increases with
decreasing halo mass).
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