Dwarf Spheroidals in MOND

TL;DR

This study analyzes the velocity dispersions of eight Milky Way dwarf spheroidal galaxies using MOND, revealing that most have reasonable mass-to-light ratios, but some pose challenges, and discusses tidal effects and the Magellanic Stream in MOND.

Contribution

The paper applies Jeans analysis in MOND to dwarf spheroidals, highlighting issues with high M/L ratios in some cases and proposing tidal effects as a potential explanation.

Findings

Six out of eight dwarfs have sensible M/L ratios using MOND.

Sextans and Draco exhibit high M/L ratios, challenging MOND predictions.

Tidal effects may disrupt Draco and influence the Magellanic Stream formation.

Abstract

We take the line of sight velocity dispersions as functions of radius for 8 Milky Way dwarf spheroidal galaxies and use Jeans analysis to calculate the mass-to-light ratios (M/L) in Modified Newtonian Dynamics (MOND). Using the latest structural parameters, distances and variable velocity anisotropy, we find 6/8 dwarfs have sensible M/L using only the stellar populations. Sextans and Draco, however, have M/L=9.2_{-3.0}^{+5.3} and 43.9_{-19.3}^{+29.0} respectively, which poses a problem. Apart from the need for Sextans' integrated magnitude to be reviewed, we propose tidal effects intrinsic to MOND, testable with numerical simulations, but fully orbit dependant, which are disrupting Draco. The creation of the Magellanic Stream is also re-addressed in MOND, the scenario being the stream is ram pressure stripped from the SMC as it crosses the LMC.