Distances to Local Group Galaxies via Population II, Stellar Distance Indicators. II. The Fornax Dwarf Spheroidal*

Abstract

Abstract We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based VI imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an I-band tip of the red giant branch (TRGB) magnitude of I 0 TRGB = 16.753 ± 0.03 stat ± 0.037 sys mag, with a calibration based in the LMC giving a distance modulus of μ 0 TRGB = 20.80 ± 0.037 stat ± 0.057 sys mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL period–luminosity and period–Wesenheit relations, we find μ 0 PLZ = 20.74 ± 0.01 stat ± 0.12 sys mag and μ 0 PWZ = 20.68 ± 0.02 stat ± 0.07 sys mag. Finally, we determine a distance from Fornax’s horizontal branch (HB) and two galactic globular cluster calibrators, giving μ 0 HB = 20.83 ± 0.03 stat ± 0.09 sys mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus 〈μ 0〉 =20.770 ± 0.042stat ± 0.024sys mag (corresponding to a distance of 143 ± 3 kpc).