Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid
Article (Faculty180)
Dark matter halos that reach the HI-cooling mass without prior star formation
or external metal pollution represent potential sites for the formation of
small Population III galaxies at high redshifts. Such objects are expected to
attain total stellar masses of at most $10^6$ solar masses and will therefore
typically be extremely faint. Gravitational lensing may in rare cases boost
their fluxes to detectable levels, but to find even a small number of such
objects requires very large sky areas to be surveyed. Because of this, a small,
wide-field telescope can in principle offer better detection prospects than a
large telescope with a smaller field of view. Here, we derive the Pop III
galaxy properties - in terms of comoving number density, stellar initial mass
function and total stellar mass - required to allow gravitational lensing to
lift such objects at redshift z = 5-16 above the detection thresholds of blind
surveys carried out with the James Webb space telescope (JWST), the Roman space
telescope (RST) or Euclid. We find that the prospects for photometric
detections of Pop III galaxies are promising, and that they are better for RST
than for JWST and Euclid. However, the Pop III galaxies favoured by current
simulations have number densities too low to allow spectroscopic detections
based on the strength of the HeII1640 emission line in any of the considered
surveys unless very high star formation efficiencies (10 per cent) are envoked.
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