Mon. Not. R. Astron. Soc., 479, 5343-5361 (2018/October-0)
Snake in the Clouds: a new nearby dwarf galaxy in the Magellanic bridge*.
KOPOSOV S.E., WALKER M.G., BELOKUROV V., CASEY A.R., GERINGER-SAMETH A., MACKEY D., DA COSTA G., ERKAL D., JETHWA P., MATEO M., OLSZEWSKI E.W. and BAILEY J.I.
Abstract (from CDS):
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 MV ∼ -4.7 and size 53 ± 3 pc, located 28 kpc from the Sun and 24 kpc from the LMC. From spectroscopy of ∼30 member stars, we measure a velocity dispersion of 2.7 ± 0.5 km s–1 and find tentative evidence for a radial velocity gradient consistent with 3 km s–1 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. The new dwarf is a metal-poor galaxy with a mean metallicity [Fe/H]=-2.5 and [Fe/H] standard deviation of 0.4 dex, similar to other systems of similar luminosity. α abundances of Hyi 1 members indicate that star formation was extended, lasting between 0.1 and 1 Gyr, with self-enrichment dominated by supernova Ia. The dwarf also hosts a highly carbon-enhanced extremely metal-poor star with [Fe/H]∼-3.2 and [C/Fe] ∼ +3.0.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
stars: general - globular clusters: general - Galaxy: halo - galaxies: dwarf - Local Group - Magellanic Clouds
NAME Hydrus I = NAME Hyi I. Table 2: [KWB2018] NNN N=139 among (Nos 1-235).
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