Improving helium abundance determinations with Leo P as a case study

Currently, the primordial helium abundance is best estimated through spectroscopic observations of HII 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 HI atoms, the effects underlying absorption in the HI and He I emission lines, and the treatment of the blended HI 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 HII region in the extremely metal-poor (3% Z(circle dot)) 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 +/- 0.0034.

Automated summary

The study improves methodologies to reduce systematic uncertainties in determining the primordial helium abundance in galaxies. By combining observations and data analysis, the uncertainty in the helium abundance of Leo P galaxy is significantly decreased, resulting in an estimated primordial helium mass fraction of Y_p = 0.2453 +/- 0.0034.