Program: GS-2007A-Q-42

Title:Dark matter lost or found? - the definitive dynamical portrait of an ordinary elliptical galaxy
PI:Aaron Romanowsky
Co-I(s): Tom Richtler, Doug Geisler, Favio Faifer, Juan Carlos Forte, Ewan O'Sullivan, Trevor Ponman, Ylva Schuberth, Andres Jordan

Abstract

Planetary nebula (PN) kinematics in ordinary elliptical galaxies show surprisingly little evidence of dark matter. This result is highly controversial, and it is crucial to confirm it with independent mass constraints, e.g. via the kinematics of globular clusters (GCs). The galaxy NGC 4697 is a prime candidate for such a check, as it is a nearby flattened "low dark matter" elliptical with a large GC population. Our previous GMOS proposal on GC kinematics in this galaxy was only half completed, but we still managed to acquire ~100 velocities, which intriguingly do support the PN result of low dark matter content. Our data set is not extensive enough yet for definitive results, so we propose to continue the program, acquiring another ~100 GC velocities around NGC 4697, with an extension to much larger radii. We will combine all of the galaxy's available data (stars, PNe, GCs, X-ray) to tightly constrain its distribution of dark matter. The dynamical properties of the GC system (rotation, orbit types, LMXB connections) will also be useful as a diagnostic of the galaxy formation history.