The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch. (arXiv:1907.05922v1 [astro-ph.CO])

The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch. (arXiv:1907.05922v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Freedman_W/0/1/0/all/0/1">Wendy L. Freedman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Madore_B/0/1/0/all/0/1">Barry F. Madore</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hatt_D/0/1/0/all/0/1">Dylan Hatt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hoyt_T/0/1/0/all/0/1">Taylor J. Hoyt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jang_I/0/1/0/all/0/1">In-Sung Jang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beaton_R/0/1/0/all/0/1">Rachael L. Beaton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burns_C/0/1/0/all/0/1">Christopher R. Burns</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_M/0/1/0/all/0/1">Myung Gyoon Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Monson_A/0/1/0/all/0/1">Andrew J. Monson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neeley_J/0/1/0/all/0/1">Jillian R. Neeley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Phillips_M/0/1/0/all/0/1">Mark M. Phillips</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rich_J/0/1/0/all/0/1">Jeffrey A. Rich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Seibert_M/0/1/0/all/0/1">Mark Seibert</a>

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 (SNeIa). We find a value of Ho = 69.8 +/-
0.8 (+/-1.1% stat) +/- 1.7 (+/-2.4% sys) km/sec/Mpc. 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-sigma level with that of the Planck 2018
estimate, and at the 1.7-sigma level with the SHoES measurement of Ho based on
the Cepheid distance scale. The TRGB distances have been measured using deep
Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) 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 (DEB)
stars, combined with an HST parallax calibration of a 3.6 micron 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 sample containing about 100
well-observed SNeIa. 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 the Cepheid sample, better matching the range of host-galaxy masses in the
CSP distant sample, and reducing potential systematic effects in the SNeIa
measurements.

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