Letarte, B. and Chapman, S. C. and Collins, M. and Ibata, R. A. and Irwin, M. J. and Ferguson, A. M. N. and Lewis, G. F. and Martin, N. and McConnachie, A. and Tanvir, N. (2009) A Keck/DEIMOS spectroscopic survey of the faint M 31 satellites And XV and And XVI. Monthly Notices of the Royal Astronomical Society, 400 (3). pp. 1472-1478. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20100108-153048383
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We present the results of a spectroscopic survey of the recently discovered M31 satellites And XV and And XVI, lying at projected distances from the centre of M31 of 93 and 130 kpc, respectively. These satellites lie to the south of M31, in regions of the stellar halo which wide-field imaging has revealed as relative voids (compared to the ~degree-scale coherent stream-like structures). Using the Deep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have defined probable members of these satellites, for which we derive radial velocities as precise as ~6 km s^(−1) down to i ~ 21.5. While the distance to And XVI remains the same as previously reported (525 ± 50 kpc), we have demonstrated that the brightest three stars previously used to define the tip of the red giant branch in And XV are in fact Galactic, and And XV is actually likely to be much more distant at 770 ± 70 kpc (compared to the previous 630 kpc), increasing the luminosity from M_V ≈ −9.4 to −9.8. The And XV velocity dispersion is resolved with v_r = −339^(+7)_(−6) km s^(−1) and σ_v = 11^(+7)_(−5) km s^(−1). The And XVI dispersion is not quite resolved at 1σ with v_r = −385^(+5)_(−6) km s^(−1) and σ = 0^(+10)_(−indef) km s^(−1) . Using the photometry of the confirmed member stars, we find metallicities of And XV (median [Fe/H] = −1.58 , interquartile range ±0.08) and And XVI (median [Fe/H] = −2.23, interquartile range ±0.12). Stacking the spectra of the member stars, we find spectroscopic [Fe/H] = −1.8 (−2.1) for And XV (And XVI), with an uncertainty of ~0.2 dex in both cases. Our measurements of And XV reasonably resolve its mass (~10^8 M_⊙) and suggest a polar orbit, while the velocity of And XVI suggests it is approaching the M31 escape velocity given its large M31 centric distance.
|Additional Information:||© 2009 RAS. Accepted 2009 August 14; received 2009 August 12; in original form 2009 January 7. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.|
|Subject Keywords:||galaxies: dwarf; galaxies: individual: And XV; galaxies: individual: And XVI; Local Group; galaxies: stellar content|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||11 Jan 2010 23:01|
|Last Modified:||26 Dec 2012 11:41|
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