The Carnegie–Chicago Hubble Program. III. The Distance to NGC 1365 via the Tip of the Red Giant Branch

• Published in: The Astrophysical journal Vol. 852; no. 1; p. 60
• Main Authors: Jang, In Sung, Hatt, Dylan, Beaton, Rachael L., Lee, Myung Gyoon, Freedman, Wendy L., Madore, Barry F., Hoyt, Taylor J., Monson, Andrew J., Rich, Jeffrey A., Scowcroft, Victoria, Seibert, Mark
• Format: Journal Article
• Language: English
• Published: Philadelphia IOP Publishing 01-01-2018
• Subjects: Astrophysics; Calibration; Galactic clusters; Galaxies; Hubble constant; Hubble Space Telescope; Luminosity; Magellanic clouds; Space telescopes; Spiral galaxies; Supernova; Supernovae; United States > US; Chicago Illinois
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aa9d92

Abstract
The Carnegie–Chicago Hubble Program (CCHP) seeks to anchor the distance scale of Type Ia supernovae via the Tip of the Red Giant Branch (TRGB) method. Based on deep
Hubble Space Telescope
ACS/WFC imaging, we present an analysis of the TRGB for the metal-poor halo of NGC 1365, a giant spiral galaxy in the Fornax cluster that was host to the Type Ia supernova SN 2012fr. We have measured the extinction-corrected TRGB magnitude of NGC 1365 to be
F
814
W
 = 27.34 ± 0.03
stat
 ± 0.04
sys
mag. In advance of future direct calibration by
Gaia
, we adopt a provisional
I
-band TRGB luminosity set at the Large Magellanic Cloud and find a true distance modulus
μ
0
 = 31.29 ± 0.04
stat
 ± 0.06
sys
mag or
D
 = 18.1 ± 0.3
stat
 ± 0.5
sys
Mpc. This measurement is in excellent agreement with recent Cepheid-based distances to NGC 1365 and reveals no significant difference in the distances derived from stars of Populations I and II for this galaxy. We revisit the error budget for the CCHP path to the Hubble constant based on the analysis presented here, i.e., that for one of the most distant Type Ia supernova hosts within our Program, and find that a 2.5% measurement is feasible with the current sample of galaxies and TRGB absolute calibration.