Constrain the Population III initial mass function

Determine the physical dependence of LATED selection and recovery fractions on the Population III initial mass function beyond the six IMF realizations sampled by the Yggdrasil and Nakajima et al. cloudy model grids.

Background

The LATED model library samples several Population III IMF assumptions, but the authors state that these realizations bracket the model grids used in the analysis rather than the full space of physically distinct IMF shapes. Because predicted equivalent widths vary substantially between IMF assumptions, the recovery fraction may depend on the true IMF distribution.

The unresolved issue is whether the adopted grid adequately represents the physical IMF and how the IMF affects the sign and magnitude of the selection dependence. Establishing this would be necessary for interpreting LATED recovery fractions as properties of an astrophysical Population III population rather than merely of the adopted template library.

References

The Pop~III IMF is unknown.

— LATED: Ly$α$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon  (2609.24588 - Li et al., 21 Sep 2026) in Section 5.1, item 3, “Uncertainties”

Converting leakage into contamination fractions requires the relative abundances of the classes in LAE samples, which are survey-specific and observationally unknown. The Pop~III recovery fraction is likewise an average over our model grid under uniform weighting of IMF, covering fraction, age and ionisation parameter, not over a physical population, so it is a property of the criteria and the library rather than the completeness of a sample. Both steps require a population prior that no current observation constrains, and we therefore defer them to future works.

— LATED: Ly$α$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon  (2609.24588 - Li et al., 21 Sep 2026) in Section 5.1, item 7, “Uncertainties”