Implications for dwarf spheroidal mass content from interloper removal

TL;DR

This study uses the caustic method to refine member star identification in dwarf spheroidal galaxies, leading to more accurate velocity dispersion profiles and insights into their dark matter content, with implications for MOND gravity theories.

Contribution

It applies the caustic method to dwarf spheroidals, improving interloper removal and providing refined dark matter estimates consistent with stellar models in a MOND framework.

Findings

Velocity dispersion profiles are smoother after interloper removal.

Two dSphs have 20% smaller velocity dispersions than previous estimates.

Dark matter content within 300pc is roughly constant across satellites.

Abstract

Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies of the Milky Way, the smallest dark matter (DM) dominated systems in the Universe. After our interloper rejection, we compute line-of-sight velocity dispersion profiles that are substantially smoother than previous results. Moreover, two dSphs have line-of-sight velocity dispersions 20% smaller than previous calculations suggested. Our Jeans modelling confirms that the DM content interior to 300pc is roughly constant with satellite luminosity. Finally, if we assume that MOND provides the true law of gravity, our identification of interlopers implies that four dSphs have mass-to-light ratios in agreement with stellar population synthesis models, whereas Carina still has a mass-to-light ratio a factor of two too large and remains a problem for MOND.