Comparing Tip of the Red Giant Branch Distance Scales: An Independent
  Reduction of the Carnegie-Chicago Hubble Program and the Value of the Hubble
  Constant
  The tip of the red giant branch has been used to measure distances to 500
nearby galaxies with the Hubble Space Telescope (HST) which are available in
the Color-Magnitude Diagrams and Tip of the Red Giant Branch (CMDs/TRGB)
catalog on the Extragalactic Distance Database (EDD). Our established methods
are employed to perform an independent reduction of the targets presented by
the Carnegie-Chicago Hubble Program (CCHP) in the series of papers culminating
in Freedman (2021). Our distinct methodology involves modeling the observed
luminosity function of red giant branch and asymptotic giant branch stars,
which differs from the edge-detection algorithms employed by the CCHP. We find
excellent agreement between distances for 11 hosts with new imaging, all at D <
20 Mpc. However, we are unable to measure the TRGB for 4 of the 5 hosts that
use archival data designed to measure distances with Cepheids, all at D > 23
Mpc. With two new HST observations taken in the halo of the megamaser host NGC
4258, the first with the same ACS F606W and F814W filters and the
post-servicing electronics used for SN Ia hosts, we then calibrate our TRGB
distance scale to the geometric megamaser distance. Using our TRGB distances,
we find a value of the Hubble Constant of $H_{0}$ = 71.5 $\pm$ 1.8 km/s/Mpc
when using either the Pantheon or Carnegie Supernova Project (CSP) samples of
supernovae. In the future, the James Webb Space Telescope will extend
measurements of the TRGB to additional hosts of SN Ia and surface brightness
fluctuation measurements for separate paths to $H_{0}$.
