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

• Published in: The Astrophysical journal Vol. 929; no. 2; p. 116
• Main Authors: Oakes, Elias K., Hoyt, Taylor J., Freedman, Wendy L., Madore, Barry F., Tran, Quang H., Cerny, William, Beaton, Rachael L., Seibert, Mark
• Format: Journal Article
• Language: English
• Published: Philadelphia IOP Publishing 01-04-2022
• Subjects: Astrophysics; Calibration; Dwarf galaxies; Galactic clusters; Galaxies; Globular clusters; Image acquisition; Local group (astronomy); Luminosity; Red giant stars; Stars & galaxies; Stellar populations
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac5b07

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 ± 0.042
stat
± 0.024
sys
mag (corresponding to a distance of 143 ± 3 kpc).