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2007MNRAS.380..281M - Mon. Not. R. Astron. Soc., 380, 281-300 (2007/September-1)
A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies.
MARTIN N.F., IBATA R.A., CHAPMAN S.C., IRWIN M. and LEWIS G.F.
Abstract (from CDS):
From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (vr= 115 ± 5km/s) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Wil1 object is not a globular cluster given its metallicity scatter over -2.0 ≲ [Fe/H] ≲ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3+2.3–1.3km/s around a systemic velocity of -12.3±2.3km/s which implies a mass-to-light ratio of ∼700 and a total mass of ∼5x105M☉ for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 107M☉ limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.
Abstract Copyright: 2007 The Authors. Journal compilation © 2007 RAS
Journal keyword(s): galaxies: dwarf - galaxies: kinematics and dynamics - Local Group - dark matter
VizieR on-line data: <Available at CDS (J/MNRAS/380/281): table1.dat table2.dat table3.dat table4.dat table5.dat>
Nomenclature: Tables 1-5: [MIC2007] JHHMMSS.ss+DDMMSS.s N=96+126+69+54+48.
Simbad objects: 388