The Fundamental Plane for cluster E and S0 galaxies

Open Access
Publisher Website
Google Scholar
Abstract
We have analysed the shape of the Fundamental Plane (FP) for a sample of 226 E and SO galaxies in 10 clusters of galaxies. We find that the distribution of galaxies is well approximated by a plane of the form log re=1.24 log σ — 0.82 log 〈I〉e+γ for photometry obtained in Gunn r. This result is in good agreement with previous determinations. The FP has a scatter of 0.084 in log re. For galaxies with velocity dispersion larger than 100 km s−1 the scatter is 0.073. If the FP is used for distance determinations this scatter is equivalent to 17 per cent uncertainties on distances to single galaxies. We find that the slope of the FP is not significantly different from cluster to cluster. Selection effects and measurement errors can introduce biases in the derived slope. The residuals of the FP correlate weakly with the velocity dispersion and the surface brightness. Some of the coefficients used in the literature give rather strong correlations between the residuals and absolute magnitudes. This implies that galaxies need to be selected in a homogeneous way to avoid biases of derived distances on the level of 5–10 per cent or smaller. The FP has significant intrinsic scatter. No other structural parameters like ellipticity or isophotal shape can reduce the scatter significantly. This is in contradiction to simple models, which predict that the presence of discs in E and SO galaxies can introduce scatter in the FP. It remains unknown what the source of scatter is. It is therefore unknown whether this source produces systematic errors in distance determinations. The Mg2–σ relation for the cluster galaxies differs slightly from cluster to cluster. Galaxies in clusters with lower velocity dispersions have systematically lower Mg2. The effect can be caused by both age and metallicity variations. With the current stellar population models, the best agreement with our results regarding the FP is if the offsets are mainly caused by differences in metallicity. Most of the distances that we derive from the FP imply small peculiar motions ( < 1000 km s−1). The zero point of the FP must therefore be quite stable. Only for one cluster, located 28° from the direction towards the ‘Great Attractor’, do we find a peculiar motion of 1300 km s−1. This motion is reduced to 890 km s−1 if we use the FP corrected for the offset of the Mg2–σ relation. This confirms earlier suggestions that the residuals from the Mg2–σ relation can be used to flag galaxies with deviant populations, and possibly to correct the distance determinations for the deviations.
All Related Versions

This publication has 0 references indexed in Scilit: