STELLAR KINEMATICS AND METALLICITIES IN THE ULTRA-FAINT DWARF GALAXY RETICULUM II
STELLAR KINEMATICS AND METALLICITIES IN THE ULTRA-FAINT DWARF GALAXY RETICULUM II
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DOI：
10.1088/0004-637x/808/1/95
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发表时间：
2015-04
期刊：
影响因子：
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通讯作者：
J. Simon;A. Drlica-Wagner;Ting S. Li;B. Nord;M. Geha;K. Bechtol;E. Balbinot;E. Buckley-Geer
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文献类型：
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作者：
J. Simon;A. Drlica-Wagner;Ting S. Li;B. Nord;M. Geha;K. Bechtol;E. Balbinot;E. Buckley-Geer
We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8 ± 0.5 km s − 1 ?> and a velocity dispersion of 3.3 ± 0.7 km s − 1 ?> . The mass-to-light ratio of Ret II within its half-light radius is 470 ± 210 M ⊙ / L ⊙ ?> , demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 km s - 1 ?> , respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 ± 0.09 dex, and we identify several extremely metal-poor stars with [Fe/H] . In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H] = - 2.65 ± 0.07 ?> , Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is log 10 ( J ) = 18.8 ± 0.6 GeV 2 cm - 5 ?> within 0.°2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.
