TY - JOUR
T1 - A spectroscopic confirmation of the bootes II dwarf spheroidal
AU - Koch, Andreas
AU - Wilkinson, Mark I.
AU - Kleyna, Jan T.
AU - Irwin, Mike
AU - Zucker, Daniel B.
AU - Belokurov, Vasily
AU - Gilmore, Gerard F.
AU - Fellhauer, Michael
AU - Evans, N. Wyn
PY - 2009
Y1 - 2009
N2 - We present a new suite of photometric and spectroscopic data for the faint Bootes II dwarf spheroidal galaxy (dSph) candidate. Our deep photometry, obtained with the Isaac Newton Telescope/Wide Field Camera, suggests a distance of 46 kpc and a small half-light radius of 4.0′ (56 pc), consistent with previous estimates. Follow-up spectroscopy obtained with the Gemini/GMOS instrument yielded radial velocities and metallicities. While the majority of our targets covers a broad range in velocities and metallicities, we find five stars that share very similar velocities and metallicities and that are all compatible with the colors and magnitudes of the galaxy's likely red giant branch. We interpret these as a spectroscopic detection of the Bootes II system. These stars have a mean velocity of -117 km s-1, a velocity dispersion of (10.5 ± 7.4) km s-1, and a mean [Fe/H] of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo II is not consistent with the stellar-mass-metallicity relation for the more luminous dwarf galaxies. Coupled with our distance estimate, its high negative systemic velocity rules out any physical connection with its projected neighbor, the Bootes I dwarf spheroidal, which has a velocity of +100 km s-1. The velocity and distance of Bootes II coincide with those of the leading arm of Sagittarius, which passes through this region of the sky, so that it is possible that Bootes II may be a stellar system associated with the Sagittarius stream. Finally, we note that the properties of Bootes II are consistent with it being the surviving remnant of a previously larger and more luminous dSph galaxy.
AB - We present a new suite of photometric and spectroscopic data for the faint Bootes II dwarf spheroidal galaxy (dSph) candidate. Our deep photometry, obtained with the Isaac Newton Telescope/Wide Field Camera, suggests a distance of 46 kpc and a small half-light radius of 4.0′ (56 pc), consistent with previous estimates. Follow-up spectroscopy obtained with the Gemini/GMOS instrument yielded radial velocities and metallicities. While the majority of our targets covers a broad range in velocities and metallicities, we find five stars that share very similar velocities and metallicities and that are all compatible with the colors and magnitudes of the galaxy's likely red giant branch. We interpret these as a spectroscopic detection of the Bootes II system. These stars have a mean velocity of -117 km s-1, a velocity dispersion of (10.5 ± 7.4) km s-1, and a mean [Fe/H] of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo II is not consistent with the stellar-mass-metallicity relation for the more luminous dwarf galaxies. Coupled with our distance estimate, its high negative systemic velocity rules out any physical connection with its projected neighbor, the Bootes I dwarf spheroidal, which has a velocity of +100 km s-1. The velocity and distance of Bootes II coincide with those of the leading arm of Sagittarius, which passes through this region of the sky, so that it is possible that Bootes II may be a stellar system associated with the Sagittarius stream. Finally, we note that the properties of Bootes II are consistent with it being the surviving remnant of a previously larger and more luminous dSph galaxy.
UR - http://www.scopus.com/inward/record.url?scp=65549140390&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/690/1/453
DO - 10.1088/0004-637X/690/1/453
M3 - Article
AN - SCOPUS:65549140390
SN - 0004-637X
VL - 690
SP - 453
EP - 462
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -