Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae

TL;DR

This study uses planetary nebulae as probes to investigate dark matter in early-type galaxies, confirming previous findings of low dark matter in some and revealing a correlation between dark matter content and galaxy luminosity.

Contribution

It introduces a new instrument, the Planetary Nebula Spectrograph, and provides comprehensive data confirming dark matter variations across different early-type galaxies.

Findings

Confirmed low dark matter in some galaxies

Observed correlation between dark matter ratio and galaxy luminosity

First complete dataset from the PN.S instrument

Abstract

We examine the dark matter properties of nearby early-type galaxies using planetary nebulae (PNe) as mass probes. We have designed a specialised instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William Herschel telescope, with the purpose of measuring PN velocities with best efficiency. The primary scientific objective of this custom-built instrument is the study of the PN kinematics in 12 ordinary round galaxies. Preliminary results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al. 2003) are now confirmed by the first complete PN.S datasets. On the other hand early-type galaxies with a "regular" dark matter content are starting to be observed among the brighter PN.S target sample, thus confirming a correlation between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and the galaxy luminosity and mass.