A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY

By J. Simon, M. Geha, Q. Minor, G. Martinez, E. Kirby, James S. Bullock, M. Kaplinghat, L. Strigari, B. Willman, P. Choi and 2 more. 2010

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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 × 105 M☉. 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☉/L☉, 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f3e802835776b2f40a79bc40ee42e7c6e0a83e9e

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Citations in the corpus

The Pristine survey - I. Mining the Galaxy for the most metal-poor stars (2017, background): “At present, most of the “mass” measurements assume dynamical equilibrium (e.g., Martin et al. 2007; Simon & Geha 2007; Simon et al. 2011), which is far from being proven for systems within a few tens of kpc.”
CONSTRAINTS ON MACHO DARK MATTER FROM COMPACT STELLAR SYSTEMS IN ULTRA-FAINT DWARF GALAXIES (2016, unknown): “†† References abbreviated as: 1 (Martin et al. 2007); 2 (Martin et al. 2008); 3 (Simon et al. 2011); 4 (Belokurov et al. 2009); 5 (Bechtol et al. 2015); 6 (Koposov et al. 2015a); 7 (Koposov et al. 2015b); 8 (Laevens et al. 2015); 9 (Crnojević et al. 2016) * Geometric means of Koposov et al.…”
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters (2018, background): “With an absolute magnitude of MV = −1.3± 0.7, it has been described as the faintest Milky Way satellite galaxy discovered to date (Geha et al. 2009; Simon et al. 2011), although it was originally classified as a diffuse globular cluster by Belokurov et al. (2007a).”
EIGHT ULTRA-FAINT GALAXY CANDIDATES DISCOVERED IN YEAR TWO OF THE DARK ENERGY SURVEY (2015, background): “…follow-up observations (Kleyna et al. 2005; Muñoz et al. 2006; Martin et al. 2007; Simon & Geha 2007; Adén et al. 2009; Belokurov et al. 2009; Carlin et al. 2009; Geha et al. 2009; Koch et al. 2009; Walker et al. 2009; Koposov et al. 2011; Simon et al. 2011; Willman et al. 2011; Kirby et al. 2013).”
Too big to fail? The puzzling darkness of massive Milky Way subhaloes (2011, background): “Kinematic constraints favor masses and densities for the ultra-faints that are indicative of fairly massive subhaloes (Strigari et al. 2008; Walker et al. 2009; Simon et al. 2010), albeit with large uncertainties at present (e.g., Wolf et al. 2010; Martinez et al. 2010).”
Small-Scale Challenges to the ΛCDM Paradigm (2017, background): “Instead, dSphs are primarily stellar dispersion-supported systems, with masses that are best probed by velocity dispersion measurements obtained star-by-star for the closest dwarfs (e.g., Walker et al. 2009; Simon et al. 2011; Kirby et al. 2014).”
THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP (2012, unknown): “…References: (1) Martin et al. 2005; (2) Ibata et al. 1994; (3) Ibata et al. 1997; (4) Peñarrubia et al. 2011; (5) Grcevich & Putman 2009; (6) Simon et al. 2011; (7) Simon & Geha 2007; (8) Koch et al. 2009; (9) Belokurov et al. 2009; (10) Martin et al. 2007; (11) Carlin et al. 2009; (12)…”
One Law to Rule Them All: The Radial Acceleration Relation of Galaxies (2016, unknown): “…et al. (2009), 31: de Jong et al. (2010), 32: Walker et al. (2009a), 33: Irwin et al. (2007), 34: de Jong et al. (2008), 35: Sand et al. (2012), 36: Simon et al. (2011), 37: Belokurov et al. (2009), 38: Kirby et al. (2013), 39: Bernard et al. (2009), 40: McConnachie (2012), 41: Fraternali et…”
Gaia DR2 proper motions of dwarf galaxies within 420 kpc (2018, methodology): “We use the catalog of Simon et al. (2011) and the membership probabilities based on a Bayesian approach.”
SEARCHING FOR DARK MATTER ANNIHILATION IN RECENTLY DISCOVERED MILKY WAY SATELLITES WITH FERMI-LAT (2016, background): “The most compact kinematically classified dSph is Segue 1 (Geha et al. 2009; Simon et al. 2011), which has an azimuthally averaged half-light radius of 21 pc.”
Dark matter annihilation and decay in dwarf spheroidal galaxies: the classical and ultrafaint dSphs (2015, methodology): “The sample for Segue I (Simon et al. 2011) includes membership probabilities that are estimated in two ways: via the same EM algorithm, and alternatively using a Bayesian analysis that considers the entire data set to be a mixture of Segue I and foreground populations.”
Galactic Searches for Dark Matter (2012, background): “Folllow up studies of Segue 1 with three times the sample of stars has shown that this result holds (Simon et al., 2011), and that it is robust to systematic effects such as binary stars (Martinez et al., 2011).”
THE SPLASH SURVEY: SPECTROSCOPY OF 15 M31 DWARF SPHEROIDAL SATELLITE GALAXIES (2011, methodology): “We also show the MW dSph compilation of Wolf et al. (2010), with updates for Boötes I and Segue 1 from Koposov et al. (2011) and Simon et al. (2011), respectively, as triangles (red).”
Cosmological Simulations with Self-Interacting Dark Matter I: Constant Density Cores and Substructure (2012, unknown): “1 core densities approach ∼ 0.01 M⊙/pc 3 – each at least a factor of∼ 3 denser than their SIDM1 counterparts.”
EIGHT NEW MILKY WAY COMPANIONS DISCOVERED IN FIRST-YEAR DARK ENERGY SURVEY DATA (2015, background): “…“ultra-faint” galaxies (Kleyna et al. 2005; Muñoz et al. 2006; Martin et al. 2007; Simon & Geha 2007; Adén et al. 2009; Belokurov et al. 2009; Carlin et al. 2009; Geha et al. 2009; Koch et al. 2009; Walker et al. 2009; Koposov et al. 2011; Simon et al. 2011; Willman et al. 2011; Kirby et al. 2013).”