The SAMI Pilot Survey: The Fundamental and Mass Planes in Three Low-Redshift Clusters

TL;DR

This study uses integral field spectroscopy of 106 galaxies in three nearby clusters to refine the Fundamental Plane and Mass Plane relations, revealing minimal scatter with specific measurement methods and potential non-linear mass-to-light ratio behavior.

Contribution

It introduces a new approach to measuring velocity dispersions and demonstrates that the Mass Plane has near-zero intrinsic scatter, advancing understanding of galaxy dynamics.

Findings

Velocity dispersions within one effective radius minimize scatter.

Mass Plane shows further reduced scatter, nearly zero.

Evidence for non-linear dynamical mass-to-light ratio relationship.

Abstract

Using new integral field observations of 106 galaxies in three nearby clusters we investigate how the intrinsic scatter of the Fundamental Plane depends on the way in which the velocity dispersion and effective radius are measured. Our spatially resolved spectroscopy, combined with a cluster sample with negligible relative distance errors allows us to derive a Fundamental Plane with minimal systematic uncertainties. From the apertures we tested, we find that velocity dispersions measured within a circular aperture with radius equal to one effective radius minimises the intrinsic scatter of the Fundamental Plane. Using simple yet powerful Jeans dynamical models we determine dynamical masses for our galaxies. Replacing luminosity in the Fundamental Plane with dynamical mass, we demonstrate that the resulting Mass Plane has further reduced scatter, consistent with zero intrinsic scatter. Using these dynamical models we also find evidence for a possibly non-linear relationship between dynamical mass-to-light ratio and velocity dispersion.