Modified Gravity Theories in Light of the Anomalous Velocity Dispersion of NGC1052-DF2

TL;DR

This paper examines whether modified gravity theories can explain the low velocity dispersion observed in galaxy NGC1052-DF2, challenging the dark matter hypothesis and finding consistency with several alternative gravity models.

Contribution

The study analyzes NGC1052-DF2's velocity dispersion within four popular modified gravity theories, showing they can account for the observations without dark matter.

Findings

Modified gravity models fit the velocity dispersion data.

Dark matter is not necessary to explain NGC1052-DF2.

Results are consistent with general relativity without dark matter.

Abstract

Recent observations of ultra-dwarf galaxy NGC1052-DF2 started an interesting discussion between dark matter hypothesis and modified gravity theories. Reported low velocity dispersion (< 10.5 km/s at 90% confidence level) derived from the kinematic data of 10 globular clusters in the galaxy points towards an extraordinarily low dynamical mass ($\sim$ $3.4 \times 10^{8} M_{\odot}$) which is of the same order of the luminous mass ($\sim$ $2.0 \times 10^{8} M_{\odot}$) in the galaxy. This has been interpreted as the first evidence of a galaxy `without Dark Matter'. It has been argued that dark matter is not necessarily coupled to the the baryonic mass on the galactic scale and poses a challenge to modified gravity theories. We explore the dynamics of NGC1052-DF2 within the context of four popular alternative theories of gravity [Modified Newtonian Dynamcies (MOND), Weyl Conformal gravity, Modified gravity (MOG)/Scalar-Tensor-Vector Gravity (STVG) and Verlinde's Emergent gravity] and present the analysis of detailed radial variation of the velocity dispersion. We demonstrate that the dispersion data of NGC1052-DF2 is fully consistent with modified gravity paradigm (as well as with general relativity without dark matter). We reach similar conclusion for the ultra-dwarf NGC1052-DF4 which has been claimed to be the second candidate for galaxies `without Dark Matter'.