RR Lyrae-based Distances for 39 Nearby Dwarf Galaxies Calibrated to Gaia eDR3

TL;DR

This paper presents highly precise RR Lyrae-based distance measurements for 39 nearby dwarf galaxies, calibrated using Gaia eDR3 data, improving accuracy and consistency over previous methods.

Contribution

It introduces a Bayesian hierarchical model for distance estimation anchored to Gaia eDR3 parallaxes, enhancing precision and addressing previous uncertainties in RR Lyrae distance scales.

Findings

Distances are 2-3 times more precise than previous literature.

Distances are on average 0.05 mag closer than literature estimates.

Gaia eDR3 parallaxes significantly improve the period-luminosity-metallicity relation.

Abstract

We provide uniform RR Lyrae-based distances to 39 dwarf galaxies in and around the Local Group. We determine distances based on a Bayesian hierarchical model that uses periods and magnitudes of published RR Lyrae in dwarf galaxies and is anchored to well-studied Milky Way (MW) RR Lyrae with spectroscopic metallicities and Gaia eDR3 parallaxes. Gaia eDR3 parallaxes for the anchor sample are a factor of 2, on average, more precise than DR2 parallaxes, and allow for a much better constrained period-luminosity-metallicity relation. While $\sim75$% of our distances are within 1-$\sigma$ of recent literature RR Lyrae distances, our distances are also $\sim2$-$3$ times more precise than literature distances, on average. On average, our distances are $\sim0.05$ mag closer than literature distances, as well as $\sim0.06$ mag closer than distances derived using a theoretical period-luminosity-metallicity relation. These discrepancies are largely due to our eDR3 parallax anchor. We show that the Hipparcos-anchored RR Lyrae distance scale of Carretta et al. (2000) over-predicts distances to MW RR Lyrae by $\sim0.05$ mag. The largest uncertainties in our distances are (i) the lack of direct metallicity measurements for RR Lyrae and (ii) the heterogeneity of published RR Lyrae photometry. We provide simple formulae to place new dwarf galaxies with RR Lyrae on a common distance scale with this work. We provide public code that can easily incorporate additional galaxies and data from future surveys, providing a versatile framework for cartography of the local Universe with RR Lyrae.