A Two-point Diagnostic for the HII Galaxy Hubble Diagram

TL;DR

This paper uses a 2-point diagnostic to compare the R_h=ct universe with Planck LCDM using HII galaxy data, finding statistical support for R_h=ct and highlighting potential non-Gaussian errors in measurements.

Contribution

It introduces a pairwise 2-point diagnostic method for cosmological model comparison using HII galaxy data, supporting R_h=ct over LCDM.

Findings

R_h=ct is statistically preferred over Planck LCDM.

Measurement errors may include non-Gaussian systematic effects.

HII galaxies can be better used as standard candles with improved systematics handling.

Abstract

A previous analysis of starburst-dominated HII Galaxies and HII regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the R_h=ct universe, over LCDM and its related dark-matter parametrizations. In this paper, we employ a 2-point diagnostic with these data to present a complementary statistical comparison of R_h=ct with Planck LCDM. Our 2-point diagnostic compares---in a pairwise fashion---the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that R_h=ct is statistically preferred over Planck LCDM. But we also find that the reported errors in the HII measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of HII Galaxies and HII regions as standard candles may be improved even further with a better handling of the systematics in these sources.