THE LEAST-LUMINOUS GALAXY: SPECTROSCOPY OF THE MILKY WAY SATELLITE SEGUE 1

By M. Geha, B. Willman, J. Simon, L. Strigari, E. Kirby, D. Law, J. Strader. 2008

189 citations recorded by the source corpus.

We present Keck/DEIMOS spectroscopy of Segue 1, an ultra–low-luminosity (MV = −1.5+0.6−0.8) Milky Way satellite companion. While the combined size and luminosity of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we present spectroscopic evidence that this object is a dark matter-dominated dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean heliocentric recession velocity of 206 ± 1.3 km s−1. Although Segue 1 spatially overlaps the leading arm of the Sagittarius stream, its velocity is 100 km s−1 different from that predicted for recent Sagittarius tidal debris at this position. We measure an internal velocity dispersion of 4.3 ± 1.2 km s−1. Under the assumption that these stars are gravitationally bound and in dynamical equilibrium, we infer a total mass of 4.5+4.7−2.5 × 105M☉ in the mass-follow-light case; using a two-component maximum-likelihood model, we determine a mass within 50 pc of 8.7+13−5.2 × 105 M☉. These imply mass-to-light (M/L) ratios of ln(M/LV) = 7.2+1.1−1.2 (M/LV = 1320+2680−940) and M/LV = 2440+1580−1775, respectively. The error distribution of the M/L is nearly lognormal, thus Segue 1 is dark matter-dominated at a high significance. Although we cannot rule out the possibility that Segue 1 has been tidally disrupted, we do not find kinematic evidence supporting tidal effects. Using spectral synthesis modeling, we derive a metallicity for the single red giant branch star in our sample of [Fe/H] = −3.3 ± 0.2 dex. Finally, we discuss the prospects for detecting gamma rays from annihilation of dark matter particles and show that Segue 1 is the most promising satellite for indirect dark matter detection. We conclude that Segue 1 is the least luminous of the ultra-faint galaxies recently discovered around the Milky Way, and is thus the least-luminous known galaxy.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/be10654cbdddabc6e057aab481f6e7949e1eff9a

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Citations in the corpus

The Masses of the Milky Way and Andromeda galaxies (2010, unknown): “…et al. (2007); 21, Belokurov et al. (2008); 22, Cioni et al. (2000); 23, Harris & Zaritsky (2006); 24, Ibata et al. (1997); 25, Kaluzny et al. (1995); 26, Queloz, Dubath & Pasquini (1995); 27, Geha et al. (2009); 28, Belokurov et al. (2009); 29, Walker et al. (2006b); 30, Zucker et al. (2006b).”
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters (2018, unknown): “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).”
ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, background): “The radial velocity of Segue 1 is vGSR = 114 km s −1 (Geha et al. 2009).”
Accurate masses for dispersion-supported galaxies (2009, background): “…of individual stars (Muñoz et al. 2005, 2006; Koch et al. 2007; Martin et al. 2007; Simon & Geha 2007; Mateo et al. 2008; Walker et al. 2009a; Geha et al. 2009, Willman et al., in preparation)16, in conjunction with the distances and stellar surface density profile parameters listed in…”
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).”
A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY (2010, background): “…Diemand, & Madau 2008; Bringmann et al. 2009; Pieri et al. 2009; Martinez et al. 2009) and for placing limits on the phase space density of dark matter particles (e.g., Hogan & Dalcanton 2000; Dalcanton & Hogan 2001; Kaplinghat 2005; Simon & Geha 2007; Strigari et al. 2008b; Geha et al. 2009).”
Galactic Searches for Dark Matter (2012, background): “…is at a distance of 23 kpc, and Coma Berenices has a luminosity of a few thousand solar luminosities and is at a distance of approximately 44 kpc. Geha et al. (2009) originally derived in detail the mass distribution of Segue 1 from a sample of 24 line-of-sight velocities, concluding that it was…”
Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites (2015, background): “…of most Milky Way dwarf spheroidals (dSphs) show that, despite having luminosities that vary over nearly five orders of magnitude, they have almost the same central densities, comparable to dark matter halos with Mpeak ∼ 3 × 109 M (Strigari et al. 2008; Geha et al. 2009; Wolf et al. 2010).”
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.”
Local-Group tests of dark-matter concordance cosmology - Towards a new paradigm for structure formation (2010, unknown): “…al. (2009), 6: Belokurov et al. (2010), 7: Coleman et al. (2007b), 8: de Jong et al. (2008), 9: de Jong et al. (2010), 10: Dall’Ora et al. (2006), 11: Geha et al. (2009), 12: Greco et al. (2008), 13: Ibata et al. (2006), 14: Koch et al. (2009), 15: Kollmeier et al. (2009), 16: Kuehn et al. (2008),…”
SEARCH FOR GAMMA-RAY EMISSION FROM DES DWARF SPHEROIDAL GALAXY CANDIDATES WITH FERMI-LAT DATA (2015, background): “Additionally, SDSS data led to the discovery of a new population of “ultra-faint” satellite galaxies, which were found to be the most DM dominated objects known (Simon & Geha 2007; Strigari et al. 2008b; Geha et al. 2009).”
Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “While Niederste-Ostholt et al. (2009) advocated its being a star cluster, additional studies have shown that it is a highly dark matter dominated galaxy (Geha et al. 2009, Simon et al. 2011).”
ACCURATE STELLAR KINEMATICS AT FAINT MAGNITUDES: APPLICATION TO THE BOÖTES I DWARF SPHEROIDAL GALAXY (2011, background): “…the measurement of stellar velocities (Hargreaves, Gilmore, et al. 1994; Koch et al. 2007; Simon & Geha 2007; Walker et al. 2007; Baumgardt et al. 2009; Geha et al. 2009; Leaman et al. 2009; Koch et al. 2009) has been to crosscorrelate against a template spectrum (Simkin 1974; Tonry & Davis 1979).”