Speaker
Description
The one-dimensional Lyα forest power spectrum is a powerful cosmological probe of matter density fluctuations in the weakly non-linear regime, providing leading constraints on the matter power spectrum and the nature of dark matter at small scales. A key astrophysical systematic, however, is contamination from correlated metal absorption, especially Si III. Standard treatments usually model the Si III contribution as a simple rescaling of the Lyα signal, but these fail to accurately capture effects on small scales that are increasingly important for present and upcoming precision measurements. We introduce a new analytical fitting function for correlated Si III absorption that is accurate, physically motivated, and readily implementable in Lyα forest analysis pipelines. The model captures physical effects neglected in earlier studies, including the distinct Lyα and Si III line profiles and a scale-dependent suppression of the Lyα–Si III cross-correlation. It is motivated and tested using the Sherwood-Relics hydrodynamical simulation suite over 2.2 <= z <= 5.0 and k < 0.2 s km^-1. Our results show that improved modelling of correlated Si III absorption will be essential for extracting robust cosmological information from current datasets such as DESI and from future high-precision Lyα forest surveys.