Nearby dwarf galaxy in Magellanic bridge

Hydrus 1 is a mildly elliptical ultrafaint system with luminosity M_V_~-4.7 and size 53+/-3pc, located 28kpc from the Sun and 24kpc from the LMC. From spectroscopy of ~30 member stars, we measure a velocity dispersion of 2.7+/-0.5 km/s and find tentative evidence for a radial velocity gradient consistent with 3km/s rotation.

Hydrus 1's velocity dispersion indicates that the system is dark matter dominated, but its dynamical mass-to-light ratio M/L=66^+29^_-20_ is significantly smaller than typical for ultrafaint dwarfs at similar luminosity. The kinematics and spatial position of Hydrus 1 make it a very plausible member of the family of satellites brought into the Milky Way by the Magellanic Clouds. While Hydrus 1's proximity and well-measured kinematics make it a promising target for dark matter annihilation searches, we find no evidence for significant gamma-ray emission from Hydrus 1.