Calibration of the Faber--Jackson relation for M31 globular clusters using HIPPARCOS data

Abstract

In this paper we present data analysis regarding globular clusters as possible extragalactic distance indicators. For this purpose, we collected all velocity dispersion measurements published for Galactic and M31 globular clusters. The slope and zero-point of the Faber--Jackson relation were calibrated using Hipparcos distance measurements, and the relation was applied to extragalactic globular clusters in M31. A distance modulus of 24.12 +/- 0.45 mag was found. This is consistent with those found by fitting the red giant branches of globular clusters (24.47 +/- 0.07) and from the peak of the globular cluster luminosity function (24.03 +/- 0.23), but is lower than the values of 24.84 +/- 0.2 mag and 24.77 +/- 0.11 mag obtained by using Hipparcos data to calibrate the Cepheid period--luminosity relation. This calibrated Faber--Jackson relation can now be used directly for other Sc galaxies with resolved globular clusters, as soon as large numbers of spectra become available, e.g. through the Very Large Telescope (VLT).