Improving Helium Abundance Determinations with Leo P as a Case Study

TL;DR

This paper enhances methods for determining primordial helium abundance by analyzing Leo P's H II region, significantly reducing uncertainties and refining the primordial helium mass fraction estimate.

Contribution

It introduces improved techniques for helium abundance measurement and applies them to Leo P, lowering systematic uncertainties in primordial helium estimates.

Findings

Helium abundance uncertainty decreased by ~70%.

Primordial helium mass fraction estimated as 0.2453 ± 0.0034.

Enhanced methodology reduces systematic errors in helium determinations.

Abstract

Currently, the primordial helium abundance is best estimated through spectroscopic observations of H II regions in metal-poor galaxies. However these determinations are limited by several systematic uncertainties which ultimately limit our ability to accurately ascertain the primordial abundance. In this study, we improve the methodologies for solving for the reddening, the emission contributions from collisional excitation of the H I atoms, the effects underlying absorption in the H I and He I emission lines, and the treatment of the blended H I and He I emission at $\lambda$3889 with the aim of lowering the systematic uncertainties in helium abundance determinations. To apply these methods, we have obtained observations of the He I $\lambda$10830 emission line in the brightest H II region in the extremely metal-poor (3$\%$ Z$_{\odot}$) galaxy Leo P with the LUCI1 instrument on the LBT. We combine this measurement with previous MODS/LBT observations to derive an improved helium abundance. In doing so, our present analysis results in a decrease in the uncertainty in the helium abundance of Leo P by approximately 70%. This result is combined with data from other observations to estimate the primordial helium mass fraction, Y$_{p}$ $=$ 0.2453 $\pm$ 0.0034.