Detailed investigations of NGC 6503 in the HI line by Begeman (1987) show that the galaxy has the usual flat rotation curve, which extends 3.7 times beyond the standard optical radius. According to its total mass-to-luminosity ratio, , and also the fraction of hydrogen mass, , the galaxy seems an ordinary late type spiral. This is why one may expect that the application of the Tully-Fisher (1977) method to it should give a reliable distance estimate. Actually, the Tully-Fisher distance modulus for NGC 6503 (Bottinelli et al. 1985) is 28.58 mag, in good agreement with the photometric modulus.
However, NGC 6503 is distinguished by its peculiar velocity. With respect to the Local Group centroid its radial velocity corresponds to km/s. Adopting a local value of the Hubble parameter H = (75 10) km/s/Mpc, and the distance 5.2 Mpc we derive for NGC 6503 a peculiar velocity km/s. According to Sharina et al. (1997) another spiral, NGC 6946, situated in the Local Void, has a distance of Mpc and a corrected radial velocity km/s, which yields a peculiar velocity of ) km/s. Thus, the two bright spirals, remarked by Peebles (1990) have a significant non-Hubble component of velocity, directed from the Local Void centre towards us. These new data back up the arguments of Karachentsev & Makarov (1996) in favour of an anisotropy of the local Hubble flow.
© European Southern Observatory (ESO) 1997
Online publication: May 26, 1998