Recalibrating the Cosmic Star Formation History

TL;DR

This paper recalibrates the cosmic star formation history using updated stellar population models, revealing significant differences in conversion factors and improving consistency with stellar mass measurements, but also introducing new discrepancies.

Contribution

It introduces new calibration coefficients based on the BPASS v2.2.1 model, extending the IMF and adjusting metallicity assumptions, to refine star formation rate estimates.

Findings

New calibration coefficients are 0.15-0.2 dex higher for UV and IR, and 0.35 dex higher for Hα.

Recalibrated star formation history aligns better with stellar mass density measurements.

New tensions arise between different star formation rate indicators.

Abstract

The calibrations linking observed luminosities to the star formation rate depend on the assumed stellar population synthesis model, initial mass function, star formation and metal enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalisation of the inferred cosmic star formation history is sensitive to these assumptions. Using v2.2.1 of the Binary Population and Spectral Synthesis (\bpass) model we determine a new set of calibration coefficients for the ultraviolet, thermal-infrared, and, hydrogen recombination lines. These ultraviolet and thermal infrared coefficients are 0.15-0.2 dex higher than those widely utilised in the literature while the H$\alpha$ coefficient is $\sim 0.35$ dex larger. These differences arise in part due to the inclusion binary evolution pathways but predominantly reflect an extension in the IMF to 300 $M_{\odot}$ and a change in the choice of reference metallicity. We use these new coefficients to recalibrate the cosmic star formation history, and find improved agreement between the integrated cosmic star formation history and the in-situ measured stellar mass density as a function of redshift. However, these coefficients produce new tension between star formation rate densities inferred from the ultraviolet and thermal-infrared and those from H$\alpha$.