Dynamics of Elliptical Galaxies with Planetary Nebulae in Modified Newtonian Dynamics

TL;DR

This study analyzes the dynamics of elliptical galaxies using planetary nebulae data within the MOND framework, showing that their behavior can be explained without dark matter, based on updated observations of seven galaxies.

Contribution

It revisits elliptical galaxy dynamics with new planetary nebulae data, confirming MOND's effectiveness in explaining their behavior without dark matter.

Findings

Galaxy dynamics are consistent with MOND predictions.

Little dark matter is needed within 6-8 effective radii.

Updated data supports previous MOND-based explanations.

Abstract

The dynamics of an elliptical galaxy within a couple of effective radii can be probed effectively by stars. However, at larger distances planetary nebulae (PNe) replace stars as the tracer of the dynamics. Making use of the motion of PNe, Romanowsky et al. (2003) measured the dynamics of three luminous elliptical galaxies (NGC821, NGC3379, and NGC4494) at large distances from the galactic center. They found that little dark matter is needed up to 6 effective radii. Milgrom & Sanders (2003) showed that this result can be understood in the framework of MOdified Newtonian Dynamics (MOND). As more data are available in the past decade, we revisit this problem. We combine PNe data (up to 6{8 effective radii) and stellar data from SAURON of 7 elliptical galaxies, including those 3 galaxies in Romanowsky et al. (2003) with updated data and 4 other galaxies which have not been analyzed before. We conclude that the dynamics of these galaxies can be well explained by MOND.