A new distance criterion for spirals in the zone of avoidance

The classical Tully-Fisher (TF) relation, used to derive distances of spiral galaxies, is not suitable in the zone of avoidance. We show that it is possible to use another form, the 21 cm Tully-Fisher relation (TF21), using only HI data. Our 4867 galaxy KLUN sample (from Nancay observations, and LEDA database) allows us to derive its slope, the zero point being fixed with a set of 18 primary calibrators: a = 1.430 +/- 0.030, b = 6.45 +/- 0.07, sigma = 0.264 for the relation log (M-HI/M-circle dot) = a x log (V-M) + b. The actual uncertainty on derived distances is roughly 30%; we expect that this scatter, and consequently the Malmquist bias effect, may be reduced by considering separately the different types. The TF21 relation appears usable to obtain distances in the zone of avoidance, and is expected to provide a competitive extragalactic distance indicator.