A high-resolution rotation curve of NGC 6822: a test-case for cold dark matter

Abstract

We present high-resolution rotation curves of the Local Group dwarf irregular galaxy NGC 6822 obtained with the Australia Telescope Compact Array. Our best curves have an angular resolution of 8 arcsec or 20 pc and contain some 250 independent points. The stellar and gas components of NGC 6822 cannot explain the shape of the curve, except for the very inner regions, and NGC 6822 is consequently very dark-matter-dominated. There is no evidence for the presence of a steep density cusp down to scales of ∼20 pc, contrary to the predictions of cold dark matter.