To peak or not to peak: Impacts of using analytical star formation histories on binary black hole masses

One of the biggest goals of gravitational wave astrophysics is to use the binary black hole (BBH) merger population to probe massive star formation and evolution across cosmic history. Modeling BBH rates and population properties over redshift is crucial to interpreting current and future gravitational wave observations in order to gain insight into binary evolution processes, formation channels, and enrichment processes. The challenge lies in that the formation of isolated, stellar-mass BBHs is strongly sensitive to their formation metallicity, which varies across redshift and environment. The star formation history, which describes the redshift evolution of the star formation rate and cosmic chemical enrichment, is therefore a critical ingredient to modeling BBH populations, but it is challenging to model and is often represented using simplified analytical forms. We investigate the effectiveness of analytical models in representing the detailed star formation history of the IllustrisTNG cosmological simulations across resolution, and whether there is a discernible impact on the BBH rates and mass distribution. We find that the analytical fits fail to capture both high-redshift and high metallicity behavior of the full simulation star formation histories, affecting the resulting BBH rates and producing an artificial peak feature in the primary mass distribution. We will discuss the implications on our work for understanding the BBH population over redshift.