Paper detail

Is Holmberg-II beyond MOND theory?

We compare the basic properties and kinematics of two gas-rich dwarf galaxies: KK246 and Holmberg II (HoII). HoII is 20 times more luminous in the blue-band than KK246 and its HI mass is a factor of 6 higher than in KK246. However, the amplitudes of the rotation curves (at the last measured point) of both galaxies are very similar, of about 40 km/s at a galactocentric radius of 7 kpc. This fact is challenging for modified theories of gravity that predict a one-to-one relation between gravity at any radius and the enclosed baryonic mass in galaxies. In particular, MOdified Newtonian Dynamics (MOND) predicts an asymptotic flat velocity of 60 km/s in HoII. Since the baryonic mass of HoII is dominated by the gas component, MOND overboosts its rotation speed even if the mass of the stellar disk is taken negligibly small. We conclude the rotation curve of HoII is probably inconsistent with MOND, unless the inclination and distance are both fine-tuned to very unlikely values.