摘要：Archival HST data taken in F606W+F814W of two different fields in the outer regions of NGC 6946 is used tomeasure a tip of the red giant branch distance to the galaxy. We employ a Bayesian maximum-likelihood modelingmethod that incorporates the completeness of the photometry, and allows us to model the luminosity function ofthe RGB population. Our two fields provide us with distances of 7.74±0.42Mpc and 7.69±0.50 Mpc,respectively. Our final distance of 7.72±0.32 Mpc is higher than most values previously published in theliterature. This has important implications for supernova measurements, as NGC 6946 is host to the most observedsupernovae (10) of any galaxy to date. We find that the supernovae in NGC 6946 are on average ∼2.3 times moreluminous than previous estimates. Our distance gives NGC 6946 a peculiar velocity of v pec = −229±29 kms −1in the Local Sheet frame. This velocity is the projected component of a substantial negative SGZ motion, indicatinga coherent motion along with the other members of the M101 wall toward the plane of the Local Sheet. The M101wall, a spur off the Local Sheet into the Local Void, is experiencing the expansion of the Local Void.
关键词：distance scale;galaxies: distances and redshifts;galaxies: individual (NGC 6946);galaxies: stellar content;Hertzsprung–Russell and C–M diagrams;large-scale structure of universe
