Jeffrey L. Carlin et al 2009 ApJ 702 L9 doi:10.1088/0004-637X/702/1/L9
Jeffrey L. Carlin1, Carl J. Grillmair2, Ricardo R. Muñoz3, David L. Nidever1 and Steven R. Majewski1
Show affiliationsWe report the results of a spectroscopic study of the Boötes III (BooIII) stellar overdensity carried out with the Hectospec multifiber spectrograph on the MMT telescope. Radial velocities have been measured for 193 BooIII candidate stars selected to have magnitudes and colors consistent with its upper main sequence and lower red giant branch, as well as a number of horizontal-branch candidates. From 20 identified candidate BooIII members, we measure a systemic velocity of V ☉ = 197.5 ± 3.8 km s–1 and a velocity dispersion of σo = 14.0 ± 3.2 km s–1. We use the somewhat large velocity dispersion and the implied highly radial orbit, along with morphological evidence from Grillmair and stellar abundances, to argue that BooIII is likely the first known object observed in a transitional state between being a bound dwarf galaxy and a completely unbound tidal stream.
98.35.Df Kinematics, dynamics, and rotation
98.56.Wm Dwarf galaxies (elliptical, irregular, and spheroidal)
95.80.+p Astronomical catalogs, atlases, sky surveys, databases, retrieval systems, archives, etc.
98.35.Ac Origin, formation, evolution, age, and star formation
Issue 1 (2009 September 1)
Received 2009 June 12, accepted for publication 2009 July 24
Published 2009 August 11
Jeffrey L. Carlin et al 2009 ApJ 702 L9
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