Modified gravity theories in light of the anomalous velocity dispersion of NGC1052-DF2

Recent observations of ultradwarf galaxy NGC1052-DF2 started an interesting discussion between dark matter hypothesis and modified gravity theories. Reported low-velocity dispersion (less than 10.5 km/s at 90% confidence level) derived from the kinematic data of ten globular clusters in the galaxy points toward an extraordinarily low dynamical mass (approximately 3.4×108 M⊙), which is of the same order of the luminous mass (approximately 2.0×108 M⊙) 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 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 dynamics (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 are fully consistent with the modified gravity paradigm (as well as with general relativity without dark matter). We reach a similar conclusion for the ultradwarf NGC1052-DF4, which has been claimed to be the second candidate for galaxies without dark matter.