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Variable Modified Newtonian Mechanics VIII: Ultra faint dwarfs in Milky Way

James Chi Chung Wong

TL;DR

This paper addresses why ultra-faint dwarfs in the Milky Way exhibit velocity dispersions that deviate from the BTFR of larger galaxies. It introduces Variable Modified Newtonian Dynamics (VMOND), where the non-Newtonian acceleration arises from a central mass in an expanding background, with an effective acceleration scale $a_0^{VM}$ that depends on turnaround redshift and radius, producing MOND-like behavior without dark matter. By analyzing density perturbation growth, high-redshift virialisation, and various galactic systems, the work derives predictions for $a_0^{VM}$ across masses and radii, and investigates scenarios where external angular momentum transfer from large voids can boost the velocity dispersions of small dwarfs like Coma Berenices and Segue 1. The findings suggest that small protogalaxies may decouple early and acquire sufficient angular momentum to yield observed dispersions, highlighting a potential testable link between turnaround history, non-Newtonian gravity, and tidal/angular-momentum effects in shaping UFD kinematics.

Abstract

Velocity dispersions of Ultra faint dwarf (UFD) galaxies are observed to deviate significantly from the Baryon Tully Fisher Relation of the massive galaxies (BTFR). We propose a solution with Variable Modified Newtonian dynamics model, which could explain this deviation.

Variable Modified Newtonian Mechanics VIII: Ultra faint dwarfs in Milky Way

TL;DR

This paper addresses why ultra-faint dwarfs in the Milky Way exhibit velocity dispersions that deviate from the BTFR of larger galaxies. It introduces Variable Modified Newtonian Dynamics (VMOND), where the non-Newtonian acceleration arises from a central mass in an expanding background, with an effective acceleration scale that depends on turnaround redshift and radius, producing MOND-like behavior without dark matter. By analyzing density perturbation growth, high-redshift virialisation, and various galactic systems, the work derives predictions for across masses and radii, and investigates scenarios where external angular momentum transfer from large voids can boost the velocity dispersions of small dwarfs like Coma Berenices and Segue 1. The findings suggest that small protogalaxies may decouple early and acquire sufficient angular momentum to yield observed dispersions, highlighting a potential testable link between turnaround history, non-Newtonian gravity, and tidal/angular-momentum effects in shaping UFD kinematics.

Abstract

Velocity dispersions of Ultra faint dwarf (UFD) galaxies are observed to deviate significantly from the Baryon Tully Fisher Relation of the massive galaxies (BTFR). We propose a solution with Variable Modified Newtonian dynamics model, which could explain this deviation.
Paper Structure (10 sections, 64 equations)

This paper contains 10 sections, 64 equations.

Table of Contents

  1. Introduction
  2. The Model
  3. Density perturbation evolution
  4. Virialisation at high redshift and $a_0^{VM}$
  5. A summary of our findings of $a_0^{VM}$ for different galactic systems
  6. Implication for allowable rotational velocities for Coma Berenices.
  7. Effect of a large Angular momentum at very high redshifts
  8. The rotating velocity due to freezed overdenstiy
  9. The turnaround point of the largest mass shell
  10. Summary