2025/09/10 by Ma, Ke, Bolton, James S., Irsic, Vid +2
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2509.08613
We present an analysis of Si III absorption and its effect on the 1D Lyα forest power spectrum using the Sherwood-Relics hydrodynamical simulation suite. In addition to oscillations from the Lyα--Si III cross correlation that are damped toward smaller scales, we find an enhancement in small-scale power that has been ignored in previous studies. We therefore develop a new analytical fitting function that captures two critical effects that have previously been neglected: distinct Lyα and Si III line profiles, and a variable ratio for coeval Lyα and Si III optical depths. In contrast to earlier work, we also predict amplitudes for the Si III power spectrum and Lyα--Si III cross power spectrum that decrease toward lower redshift due to the hardening metagalactic UV background spectrum at z\lesssim 3.5. The fitting function is validated by comparison against multiple simulated datasets at redshifts 2.2≤ z ≤ 5.0 and wavenumbers k < 0.2\rm s km-1. Our model has little effect on existing warm dark matter constraints from the Lyα forest when adopting a physically motivated prior on the silicon abundance. It will, however, be an essential consideration for future, high precision Lyα forest power spectrum measurements.