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.

A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A*

“…We overplot the rotating (v/vcrit = 0.4) MESA Isochrones and Stellar Tracks (MIST; Choi et al 2016;Dotter 2016) for reference. We shift the tracks to the Gaia eDR3-anchored distance modulus of μ = 24.40 mag reported by Nagarajan et al (2022) and A v = 0.03 mag, consistent with the foreground maps of Schlafly & Finkbeiner (2011). We do not apply any further dust corrections, since Leo A shows little internal redding (Skillman et al 1989;van Zee et al 2006).…”

“…The latter is especially important as there are few extremely metal-poor systems in which individual massive stars can be resolved and high-quality spectra can be acquired. Leo A is an ideal test bed as it is the closest of the star-forming extremely metal-poor dwarf galaxies known in the local universe (D ∼ 760 kpc, Z ∼ 5% Z e ; e.g., van Zee et al 2006;Nagarajan et al 2022). Despite its favorable distance, low metallicity, and sizable massive star population (e.g., Cole et al 2007), there has not yet been a systematic investigation of massive metal-poor star properties in Leo A.…”

Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies

“…In the second suite, we consider a future version of the first suite where the proper motions and distances are improved to a level we expect in the next 5 yr. For the proper motions, we assume uncertainties based on 10 yr of Gaia data (DR5). For the distances, we assume a 2% error, which is an obtainable projection given current systematics in the period-Wesenheitmetallicity relations of RR Lyrae stars (e.g., Nagarajan et al 2022;Garofalo et al 2022). We leave the uncertainties in the MW potential and LMC potential at their present-day uncertainties to assess whether these need to be improved to make use of upcoming data.…”

CHAOS. VII. A Large-scale Direct Abundance Study in M33

“…There are many distances to M33 in the literature to choose from (see discussion in de Grijs et al 2017;Lee et al 2022). We adopt the distance modulus of 24.67 ± 0.06 (corresponding to -+ 859 23 24 kpc) based on HST observations of RR Lyrae (Savino et al 2022) anchored to the GAIA eDR3 reference frame (Nagarajan et al 2022), which is consistent with the values favored by de Grijs et al (2017) and Lee et al (2022). The effective radius of M33, R e , is determined from the z0MGS WISE 3.4 μm maps (Leroy et al 2019) with the same fitting method that is described in Leroy et al (2021) and has been utilized in previous CHAOS studies (e.g., Berg et al 2020).…”