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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 731926.0, MPI für Astronomie / Publikationen_mpia
Is Draco II one of the faintest dwarf galaxies? First study from Keck/DEIMOS spectroscopy
Authors:Martin, N. F.; Geha, M.; Ibata, R. A.; Collins, M. L. M.; Laevens, B. P. M.; Bell, E. F.; Rix, H.-W.; Ferguson, A. M. N.; Chambers, K. C.; Wainscoat, R. J.; Waters, C.
Date of Publication (YYYY-MM-DD):2016
Title of Journal:Monthly Notices of the Royal Astronomical Society
Issue / Number:1
Start Page:L59
End Page:L63
Audience:Not Specified
Abstract / Description:We present the first spectroscopic analysis of the faint and compact stellar system Draco II (Dra II, MV = -2.9 ± 0.8, r_h=19^{+8}_{-6} pc), recently discovered in the Panoramic Survey Telescope and Rapid Response System 1 3π survey. The observations, conducted with DEIMOS on the Keck II telescope, establish some of its basic characteristics: the velocity data reveal a narrow peak with nine member stars at a systemic heliocentric velocity < v_rrangle =-347.6^{+1.7}_{-1.8} km s^{-1}, thereby confirming Dra II is a satellite of the Milky Way; we infer a velocity dispersion with σvr = 2.9 ± 2.1 km s-1 (<8.4 km s-1 at the 95 per cent confidence level), which implies log _{10}(M_{1/2})=5.5^{+0.4}_{-0.6} and log _{10}(({M/L})_{1/2})=2.7^{+0.5}_{-0.8}, in Solar units; furthermore, very weak calcium triplet lines in the spectra of the high signal-to-noise member stars imply [Fe/H] < -2.1, whilst variations in the line strengths of two stars with similar colours and magnitudes suggest a metallicity spread in Dra II. These new data cannot clearly discriminate whether Draco II is a star cluster or amongst the faintest, most compact, and closest dwarf galaxies. However, the sum of the three - individually inconclusive - pieces of evidence presented here seems to favour the dwarf galaxy interpretation.
Free Keywords:galaxies: individual: Draco II; galaxies: kinematics and dynamics; Local Group
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0035-8711 %R 10.1093/mnrasl/slw013
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