Letter to the Editor

The extragalactic Cepheid distance bias: Numerical simulations

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

Corresponding author: G. Paturel, patu@obs.univ-lyon1.fr

Received: 6 October 2003
Accepted: 27 November 2003

Abstract

We present numerical simulations for a selection bias in the extragalactic Cepheid method (as detected in Teerikorpi & Paturel [CITE]), which results in underestimated distances for host galaxies. The selection effect involves the Cepheid detection magnitude limits in V and I, the dispersion in , and importantly, variation amplitude, observable upper period limit, and also extinction. It influences both the bias curve fitting method and the method where short-period Cepheids are removed. When V, I, and P-limits exist, one expects a typical bias pattern in the vs. diagram. A full bias correction is possible only for special favourable situations, but there always appears a nearly unbiased plateau. The simulated bias varies from galaxy-to-galaxy roughly as was revealed by the strong and puzzling observed trend for galaxies in TP02.