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

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 ∼75% of our distances are within 1σ of recent RR Lyrae distances in the literature, our distances are also ∼2–3 times more precise than distances in the literature, on average. On average, our distances are ∼0.05 mag closer than distances in the literature, as well as ∼0.06 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. overpredicts distances to MW RR Lyrae by ∼0.05 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 a public code that can easily incorporate additional galaxies and data from future surveys, providing a versatile framework for the cartography of the local universe with RR Lyrae.