Statistical significance of poorer high-mass spectral matches

Determine whether the tendency for the mean and median LzLCS+ stacks in the high-mass bin to have larger chi-squared values than lower-mass stacks is statistically significant when comparing them with mock Si II λ1260 and C II λ1334 spectra from the radiation-hydrodynamic simulation.

Background

The paper compares stacked Si II λ1260 and C II λ1334 absorption profiles from LzLCS+ galaxies with 22,500 mock spectra generated from a single radiation-hydrodynamic simulation. Although the simulated profiles generally reproduce the observations well, the authors note that the chi-squared distributions for the mean and median stacks extend toward higher values in the high-mass stellar-mass bin.

The authors do not establish whether this apparent degradation in the quality of the high-mass fits reflects a real physical limitation of the single-galaxy simulation or is instead caused by the limited sample size and observational uncertainties. Resolving this issue would clarify whether the simulation systematically fails to reproduce the absorption profiles of more massive galaxies.