Globular cluster orbital decay in dwarf galaxies with MOND and CDM: Impact of supernova feedback

TL;DR

This study compares globular cluster orbital decay in dwarf galaxies under Newtonian and MOND gravity, highlighting the role of supernova feedback and its implications for galaxy structure and gravity theories.

Contribution

It provides the first detailed simulation analysis of supernova feedback effects on globular cluster sinking in both Newtonian and MOND frameworks.

Findings

Supernova feedback can prevent GCs from sinking in low-mass cases in both models.

Massive GCs still sink in MOND, forming offset core-like structures.

Results favor Newtonian gravity over QUMOND in explaining GC dynamics.

Abstract

Dynamical friction works very differently for Newtonian gravity with dark matter and in modified Newtonian dynamics (MOND). While the absence of dark matter considerably reduces the friction in major galaxy mergers, analytic calculations indicate the opposite for very small perturbations, such as globular clusters (GCs) sinking in dwarf galaxies. Here, we study the decay of GCs in isolated gas-rich dwarf galaxies using simulations with the Phantom of Ramses code, which enables both the Newtonian and the QUMOND MOND gravity. We modeled the GCs as point masses, and we simulated the full hydrodynamics, with star formation and supernovae feedback. We explored whether the fluctuations in gravitational potential caused by the supernovae can prevent GCs from sinking toward the nucleus. For GCs of typical mass or lighter, we find that this indeed works in both Newtonian and MOND simulations. The GC can even make a random walk. However, we find that supernovae cannot prevent massive GCs ($M\geq 4\times10^5\,M_\odot$) from sinking in MOND. The resulting object looks similar to a galaxy with an offset core, which embeds the sunk GC. The problem is much milder in the Newtonian simulations. This result thus favors Newtonian over QUMOND gravity, but we note that it relies on the correctness of the difficult modeling of baryonic feedback. We propose that the fluctuations in the gravitational potential could be responsible for the thickness of the stellar disks of dwarf galaxies and that strong supernova winds in modified gravity can transform dwarf galaxies into ultra-diffuse galaxies.