An improved model for the effect of correlated Si iii absorption on the one-dimensional Lyman-α forest power spectrum

We present an analysis of Si iii absorption and its effect on the one-dimensional Ly forest power spectrum using the Sherwood–Relics hydrodynamical simulation suite. In addition to oscillations from the Ly – Si iii cross-correlation that are damped towards 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 Ly and Si iii line profiles, and a variable ratio for coeval Ly and Si iii optical depths. In contrast to earlier work, we also predict amplitudes for the Si iii power spectrum and Ly – Si iii cross power spectrum that decrease towards lower redshift due to the hardening metagalactic UV background spectrum at . The fitting function is validated by comparison against multiple simulated data sets at redshifts and wavenumbers s km. Our model has little effect on existing warm dark matter constraints from the Ly forest when adopting a physically motivated prior on the silicon abundance. It will, however, be an essential consideration for future, high precision Ly forest power spectrum measurements.