Astrophys. J., 692, 1464-1475 (2009/February-3)
The least-luminous galaxy: spectroscopy of the Milky Way satellite Segue 1.
GEHA M., WILLMAN B., SIMON J.D., STRIGARI L.E., KIRBY E.N., LAW D.R. and STRADER J.
Abstract (from CDS):
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. Although Segue 1 spatially overlaps the leading arm of the Sagittarius stream, its velocity is 100 km/s 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. 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 x105 M☉ in the mass-follow-light case; using a two-component maximum-likelihood model, we determine a mass within 50 pc of 8.7+13–5.2x105 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.
galaxies: dwarf - galaxies: individual: Segue 1 - galaxies: kinematics and dynamics - Local Group
VizieR on-line data:
<Available at CDS (J/ApJ/692/1464): table2.dat>
Table 2: [GWS2009] NNNNNNN N=51 among (Nos 1829185-3517219).
Table 2, col(1): NNNNNNN are the last 7 digits of SDSS DR6 objID.
View the references in ADS
To bookmark this query, right click on this link: simbad:2009ApJ...692.1464G and select 'bookmark this link' or equivalent in the popup menu