Keywords :
stars general - globular clusters: general - Galaxy: halo - galaxies: dwarf - Local Group - Magellanic Clouds
Abstract:We report the discovery of a nearby dwarf galaxy in the constellation of Hydrus, between the Large (LMC) and the Small Magellanic Clouds (SMC). 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
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