A spectroscopic confirmation of the Bootes II dwarf spheroidal - AstrophysicsReport as inadecuate

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Abstract: We present a new suite of photometric and spectroscopic data for the faintBootes II dwarf spheroidal galaxy candidate. Our deep photometry, obtained withthe INT-WFC, suggests a distance of 46 kpc and a small half-light radius of 4.0arcmin 56 pc, consistent with previous estimates. Follow-up spectroscopyobtained with the Gemini-GMOS instrument yielded radial velocities andmetallicities. While the majority of our targets covers a broad range invelocities and metallicities, we find five stars which share very similarvelocities and metallicities and which are all compatible with the colors andmagnitudes of the galaxy-s likely red giant branch. We interpret these as aspectroscopic detection of the Bootes II system. These stars have a meanvelocity of -117 km-s, a velocity dispersion of 10.5+-7.4 km-s and a meanFe-H of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo IIis not consistent with the stellar-mass-metallicity relation for the moreluminous dwarf galaxies. Coupled with our distance estimate, its high negativesystemic velocity rules out any physical connection with its projectedneighbor, the Bootes I dwarf spheroidal, which has a velocity of ~+100 km-s.The velocity and distance of Bootes II coincide with those of the leading armof Sagittarius, which passes through this region of the sky, so that it ispossible that Bootes II may be a stellar system associated with the Sagittariusstream. Finally, we note that the properties of Bootes II are consistent withbeing the surviving remnant of a previously larger and more luminous dSphgalaxy.

Author: A. Koch, M.I. Wilkinson, J.T. Kleyna, M. Irwin, D.B. Zucker, V. Belokurov, G.F. Gilmore, M. Fellhauer, N.W. Evans

Source: https://arxiv.org/

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