Letter to the Editor

Evidence for the extragalactic Cepheid distance bias from the kinematical distance scale

¹ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
² CRAL–Observatoire de Lyon, 69561 Saint-Genis Laval Cedex, France

Corresponding author: P. Teerikorpi, pekkatee@oj287.astro.utu.fi

Received: 11 July 2001
Accepted: 18 November 2001

Abstract

We present new evidence for the extragalactic Cepheid distance bias. A dependence between the Hubble parameter and the absolute Cepheid magnitude limit for a galaxy may be interpreted as a significant bias in the derived photometric distances: those from Cepheid samples with a bright absolute magnitude limit apparently are underestimated. This may be caused not only by the dispersion of at a fixed Cepheid period, but also by the whole amplitude of variation, together with an upper limit in the period of the observed Cepheids, and other factors. If so, then the value of H₀ based on methods using Cepheid distances is expected to be often overestimated (i.e. the distances underestimated). We discuss whether the effect could be not real, but rather caused by uncertainties in kinematical distances.