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Date and Time of the Query: 2019-05-25 T20:01:05 PDT
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For refcode 2011ApJ...733...46S:
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2011ApJ...733...46S A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy Simon, Joshua D.; Geha, Marla; Minor, Quinn E.; Martinez, Gregory D.; Kirby, Evan N.; Bullock, James S.; Kaplinghat, Manoj; Strigari, Louis E.; Willman, Beth; Choi, Philip I.; Tollerud, Erik J.; Wolf, Joe Abstract. We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 98.2% of the stars within 67 pc (10', or 2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r = 21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87 pc. After correcting for the influence of binary stars using repeated velocity measurements, we determine a velocity dispersion of 3.7^+1.4^_- 1.1_ km s^-1^. The mass within the half-light radius is 5.8^+8.2^_- 3.1_ x 10^5^ M_sun_. The stellar kinematics of Segue 1 require very high mass-to-light ratios unless the system is far from dynamical equilibrium, even if the period distribution of unresolved binary stars is skewed toward implausibly short periods. With a total luminosity less than that of a single bright red giant and a V-band mass-to-light ratio of 3400 M_sun_/L_sun_, Segue 1 is the darkest galaxy currently known. We critically re-examine recent claims that Segue 1 is a tidally disrupting star cluster and that kinematic samples are contaminated by the Sagittarius stream. The extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large metallicity spread among the members demonstrate conclusively that Segue 1 is a dwarf galaxy, and we find no evidence in favor of tidal effects. We also show that contamination by the Sagittarius stream has been overestimated. Segue 1 has the highest estimated dark matter density of any known galaxy and will therefore be a prime testing ground for dark matter physics and galaxy formation on small scales. Key words: dark matter, galaxies: dwarf, galaxies: individual: Segue 1, galaxies: kinematics and dynamics, Local Group
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