Determining the primordial helium abundance and UV background using fluorescent emission in star-free dark matter haloes

Abstract

Observational measures of the primordial helium mass fraction, $Y_{\mathrm{P}}$, are of interest for cosmology and fundamental particle physics. Current measures obtained from H II regions agree with the Standard Model prediction to approximately 1% precision, although these determinations may be affected by systematic uncertainties. This possibility can only be tested by independently measuring the helium abundance in new ways. Here, we propose a novel method to obtain a measurement of $Y_{\mathrm{P}}$ using hydrogen and helium recombination line emission from RELHICs: pristine, gas-rich but star-free low-mass dark matter haloes whose existence is predicted by hydrodynamical simulations. Although expected to be uncommon and intrinsically faint in emission, the primordial composition and simple physical properties of these objects make them an ideal laboratory to determine $Y_{\mathrm{P}}$. We present radiative transfer simulations to demonstrate the effectiveness of this approach, finding that comparing the emission in H and He lines, either via their volumetric emissivities, or integrated properties such as the surface brightness and total flux, may be used to infer $Y_{\mathrm{P}}$. Furthermore, we show that RELHICs can be used to provide an entirely novel constraint on the spectral slope of the ultraviolet background, and discuss the possibility of measuring this slope and the primordial helium abundance simultaneously.

10 pages, 9 figures. Accepted for publication in MNRAS

References in corpus (11)

• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Massloss of galaxies due to a UV-background
• The effects of He I 10830 on helium abundance determinations
• The primordial abundance of 4He: a self-consistent empirical analysis of systematic effects in a large sample of low-metallicity HII regions
• Metal-enriched, sub-kiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy
• A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?
• The properties of "dark" ΛCDM halos in the Local Group
• Determination of the primordial helium abundance based on NGC 346 an HII region of the Small Magellanic Cloud
• A Bayesian direct method implementation to fit emission line spectra: Application to the primordial He abundance determination
• Uncertainties in Theoretical HeI Emissivities: HII Regions, Primordial Abundance, and Cosmological Recombination
• Fluorescent rings in star-free dark matter haloes