Gaseous drag on a gravitational perturber in Modified Newtonian Dynamics and the structure of the wake

TL;DR

This paper analyzes the structure of gaseous wakes and dynamical friction on a gravitational perturber in MOND, comparing it to Newtonian gravity, with implications for galaxy and cluster evolution.

Contribution

It provides a detailed calculation of wake structures and dynamical friction in MOND, extending understanding beyond Newtonian gravity with dark matter.

Findings

Wake structure in MOND scales with mu^{-1}(g_ext/a_0)

Dynamical drag force differs from Newtonian predictions

Implications for orbit evolution of clusters and X-ray emissions

Abstract

We calculate the structure of a wake generated by, and the dynamical friction force on, a gravitational perturber travelling through a gaseous medium of uniform density and constant background acceleration g_ext, in the context of Modified Newtonian Dynamics (MOND). The wake is described as a linear superposition of two terms. The dominant part displays the same structure as the wake generated in Newtonian gravity scaled up by a factor mu^{-1}(g_ext/a_0), where a_{0} is the constant MOND acceleration and mu the interpolating function. The structure of the second term depends greatly on the angle between g_{ext} and and the velocity of the perturber. We evaluate the dynamical drag force numerically and compare our MOND results with the Newtonian case. We mention the relevance of our calculations to orbit evolution of globular clusters and satellites in a gaseous proto-galaxy. Potential differences in the X-ray emission of gravitational galactic wakes in MOND and in Newtonian gravity with a dark halo are highlighted.