High-Redshift Galaxies with Large Ionization Parameters
  Motivated by recent observations of galaxies dominated by emission lines,
which show evidence of being metal poor with young stellar populations, we
present calculations of multiple model grids with a range of abundances,
ionization parameters, and stellar ages, finding that the predicted spectral
line diagnostics are heavily dependent on all three parameters. These new model
grids extend the ionization parameter to larger values than typically explored.
We compare these model predictions with previous observations of such objects,
including two new Lyman-$\alpha$ emitting galaxies (LAE) that we have observed.
Our models give improved constraints on the metallicity and ionization
parameter of these previously studied objects, as we are now able to consider
high ionization parameter models. However, similar to previous work, these
models have difficulty predicting large line diagnostics for high ionization
potential species, requiring future work refining the modelling of FUV photons.
Our model grids are also able to constrain the metallicity and ionization
parameter of our LAEs, and give constraints on their Ly$\alpha$ escape
fractions, all of which are consistent with recent lower redshift studies of
LAEs.
