A Robust Tip of the Red Giant Branch Distance to the Fireworks Galaxy
  (NGC 6946)
  Archival HST data taken in F606W+F814W of two different fields in the outer
regions of NGC 6946 is used to measure a tip of the red giant branch (TRGB)
distance to the galaxy. We employ a Bayesian maximum-likelihood modeling method
that incorporates the completeness of the photometry, and allows us to model
the luminosity function of the RGB population. Our two fields provide us with
distances of 7.74 $\pm$ 0.42 Mpc and 7.69 $\pm$ 0.50 Mpc, respectively. Our
final distance of 7.72 $\pm$ 0.32 Mpc is higher than most values published
previously in the literature. This has important implications for supernova
measurements, as NGC 6946 is host to the most observed supernovae (10) of any
galaxy to date. We find that the supernovae in NGC 6946 are on average $\sim$
2.3 times more luminous than previous estimates. Our distance gives NGC 6946 a
peculiar velocity of $v_{pec}$ = $-229$ $\pm$ $29$ km/s in the Local Sheet
frame. This velocity is the projected component of a substantial negative SGZ
motion, indicating a coherent motion along with the other members of the M101
wall toward the plane of the Local Sheet. The M101 wall, a spur off the Local
Sheet into the Local Void, is experiencing the expansion of the Local Void.
