The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch

• Published in: The Astrophysical journal Vol. 882; no. 1; p. 34
• Main Authors: Freedman, Wendy L., Madore, Barry F., Hatt, Dylan, Hoyt, Taylor J., Jang, In Sung, Beaton, Rachael L., Burns, Christopher R., Lee, Myung Gyoon, Monson, Andrew J., Neeley, Jillian R., Phillips, M. M., Rich, Jeffrey A., Seibert, Mark
• Format: Journal Article
• Language: English
• Published: Philadelphia IOP Publishing 01-09-2019
• Subjects: Astrophysics; Binary stars; Blending effects; Calibration; Cepheid variables; Distance measurement; Eclipsing binary stars; Galactic halos; Galaxies; Halos; Hubble constant; Hubble Space Telescope; Magellanic clouds; Metallicity; Parallax; Space telescopes; Supernova; Supernovae
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab2f73

Abstract
We present a new and independent determination of the local value of the Hubble constant based on a calibration of the tip of the red giant branch (TRGB) applied to Type Ia supernovae (SNe Ia). We find a value of
H
0
 = 69.8 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s
−1
Mpc
−1
. The TRGB method is both precise and accurate and is parallel to but independent of the Cepheid distance scale. Our value sits midway in the range defined by the current Hubble tension. It agrees at the 1.2
σ
level with that of the Planck Collaboration et al. estimate and at the 1.7
σ
level with the
Hubble Space Telescope
(
HST
)
SHoES
measurement of
H
0
based on the Cepheid distance scale. The TRGB distances have been measured using deep
HST
Advanced Camera for Surveys imaging of galaxy halos. The zero-point of the TRGB calibration is set with a distance modulus to the Large Magellanic Cloud of 18.477 ± 0.004 (stat) ± 0.020 (sys) mag, based on measurement of 20 late-type detached eclipsing binary stars, combined with an
HST
parallax calibration of a 3.6
μ
m Cepheid Leavitt law based on
Spitzer
observations. We anchor the TRGB distances to galaxies that extend our measurement into the Hubble flow using the recently completed Carnegie Supernova Project I ( CSP-I ) sample containing about 100 well-observed SNe Ia . There are several advantages of halo TRGB distance measurements relative to Cepheid variables; these include low halo reddening, minimal effects of crowding or blending of the photometry, only a shallow (calibrated) sensitivity to metallicity in the
I
band, and no need for multiple epochs of observations or concerns of different slopes with period. In addition, the host masses of our TRGB host-galaxy sample are higher, on average, than those of the Cepheid sample, better matching the range of host-galaxy masses in the CSP-I distant sample and reducing potential systematic effects in the SNe Ia measurements.