The Pantheon+ Analysis: Evaluating Peculiar Velocity Corrections in
  Cosmological Analyses with Nearby Type Ia Supernovae
  Separating the components of redshift due to expansion and peculiar motion in
the nearby universe ($z<0.1$) is critical for using Type Ia Supernovae (SNe Ia)
to measure the Hubble constant ($H_0$) and the equation-of-state parameter of
dark energy ($w$). Here, we study the two dominant 'motions' contributing to
nearby peculiar velocities: large-scale, coherent-flow (CF) motions and
small-scale motions due to gravitationally associated galaxies deemed to be in
a galaxy group. We use a set of 584 low-$z$ SNe from the Pantheon+ sample, and
evaluate the efficacy of corrections to these motions by measuring the
improvement of SN distance residuals. We study multiple methods for modeling
the large and small-scale motions and show that, while group assignments and CF
corrections individually contribute to small improvements in Hubble residual
scatter, the greatest improvement comes from the combination of the two
(relative standard deviation of the Hubble residuals, Rel. SD, improves from
0.167 to 0.157 mag). We find the optimal flow corrections derived from various
local density maps significantly reduce Hubble residuals while raising $H_0$ by
$\sim0.4$ km s$^{-1}$ Mpc$^{-1}$ as compared to using CMB redshifts,
disfavoring the hypothesis that unrecognized local structure could resolve the
Hubble tension. We estimate that the systematic uncertainties in cosmological
parameters after optimally correcting redshifts are 0.06-0.11 km s$^{-1}$
Mpc$^{-1}$ in $H_0$ and 0.02-0.03 in $w$ which are smaller than the statistical
uncertainties for these measurements: 1.5 km s$^{-1}$ Mpc$^{-1}$ for $H_0$ and
0.04 for $w$.
