*Astron. Astrophys. 325, 33-40*
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## On the derivation of the Tully-Fisher relations
### II. Field galaxies, the inverse TF slope and the Hubble constant
**T. Ekholm and P. Teerikorpi**
Tuorla Observatory, University of Turku,
FIN-21500 Piikkiö, Finland
*Received 24 October 1996 / Accepted 11 March 1997*
**Abstract**
The Hubble constant *H*_{0} should not show distance-dependence.
An inappropriate use of the direct Tully-Fisher relation may lead to
a conclusion that *H*_{0} is dependent on the distance.
This paper tries to answer the question: is
it possible to avoid the caveats of the direct relation by applying
the inverse Tully-Fisher relation. Under ideal conditions it is
possible simultaneously to determine the inverse slope precisely and
to find the Hubble constant next to calibration. Ideal conditions
are, however, rarely met. Two particular sources of error in the
resulting average Hubble constant are considered. A progressive
measurement error in angular diameters (apparent magnitudes) causes
overestimation of *H*_{0}. An asymmetry in the
log *V*_{max}-distribution in the sense of a tail of small
rotational velocities tends to shift *H*_{0} upwards.
**Key words: **distance scale
*Send offprint requests to:* T. Ekholm
© European Southern Observatory (ESO) 1997
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