Journal Article

Study of the Sextans dwarf spheroidal galaxy from the DART Ca <span class="smallCaps">ii</span> triplet survey*

G. Battaglia, E. Tolstoy, A. Helmi, M. Irwin, P. Parisi, V. Hill and P. Jablonka

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 411, issue 2, pages 1013-1034
Published in print February 2011 | ISSN: 0035-8711
Published online February 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17745.x
Study of the Sextans dwarf spheroidal galaxy from the DART Ca ii triplet survey*

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We use Very Large Telescope (VLT)/Fibre Large Array Multi Element Spectrograph (FLAMES) intermediate-resolution (R∼ 6500) spectra of individual red giant branch stars in the near-infrared Ca ii triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (±2 km s−1) and CaT [Fe/H] measurements (±0.2 dex). We use the Mg i line at 8806.8 Å as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf stars). Sextans shows a similar chemodynamical behaviour to other Milky Way dSphs, with its central regions being more metal rich than the outer parts and with the more metal-rich stars displaying colder kinematics than the more metal-poor stars. Hints of a velocity gradient are found along the projected major axis and along an axis at position angle (PA) = 191°, however, a larger and more spatially extended sample may be necessary to pin down the amplitude and direction of this gradient. We detect a cold kinematic substructure at the centre of Sextans, consistent with being the remnant of a disrupted very metal poor stellar cluster. We derive the most extended line-of-sight velocity dispersion profile for Sextans, out to a projected radius of 1°.6. From Jeans modelling of the observed line-of-sight velocity dispersion profile we find that this is consistent with both a cored dark matter halo with large core radius and cuspy halo with low concentration. The mass within the last measured point is in the range 2–4 × 108 M, giving very large mass-to-light ratios, from 460 to 920 (M/L)V, ⊙.

Keywords: stars: abundances; galaxies: dwarf; galaxies: individual: Sextans dSph; galaxies: kinematics and dynamics; Local Group; dark matter

Journal Article.  17361 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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