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 tha t 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 o bservations, and LEDA database) allows us to derive its slope, the zer o 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 di stances is roughly 30%; we expect that this scatter, and consequently the Malmquist bias effect, may be reduced by considering separately th e different types. The TF21 relation appears usable to obtain distance s in the zone of avoidance, and is expected to provide a competitive e xtragalactic distance indicator.