Abstract
Direct observational searches for Population III (Pop III) stars at
high-redshift are faced with the question of how to select the most promising
targets for spectroscopic follow up. To help answer this, we use a large-scale
cosmological simulation, augmented with a new subgrid model that tracks the
fraction of pristine gas, to follow the evolution of high-redshift galaxies and
the Pop III stars they contain. We generate rest-frame ultraviolet (UV)
luminosity functions for our galaxies and find that they are consistent with
current $z 7 $ observations. Throughout the redshift range $7 z 16$
we identify 'Pop III-bright' galaxies as those with at least 75% of their flux
coming from Pop III stars. While less than 5% of galaxies brighter than $m_\rm
UV, AB = 31.4$ mag are Pop III-bright between $7z łeq8$, roughly a third
of such galaxies are Pop III-bright at $z=9$, right before reionization occurs
in our simulation. Moving to $z=10$, $m_UV, AB = 31.4$ mag corresponds to
more luminous galaxies and the Pop III-bright fraction falls off to 15%.
Finally at the highest redshifts, a large fraction of all galaxies are Pop
III-bright regardless of magnitude. While $m_UV, AB = 31.4$ mag galaxies
are likely not detectable during this epoch, we find 90% of galaxies at $z =
16$ are Pop III-bright with $m_UV, AB 33$ mag, a lensed magnitude
limit within reach of the James Webb Space Telescope. Thus we predict that the
best redshift to search for luminous Pop III-bright galaxies is just before
reionization, while lensing surveys for fainter galaxies should push to the
highest redshifts possible.
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