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Astron. Astrophys. 325, 33-40 (1997)

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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


The Hubble constant [FORMULA] should not show distance-dependence. An inappropriate use of the direct Tully-Fisher relation may lead to a conclusion that [FORMULA] 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 [FORMULA]. An asymmetry in the [FORMULA] -distribution in the sense of a tail of small rotational velocities tends to shift [FORMULA] upwards.

Key words: distance scale

Send offprint requests to: T. Ekholm


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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998