A wide angle view of the Sagittarius dwarf Spheroidal Galaxy. I: VIMOS photometry and radial velocities across Sgr dSph major and minor axis

Astronomy and Astrophysics (Impact Factor: 4.48). 11/2009; DOI: 10.1051/0004-6361/200913331
Source: arXiv

ABSTRACT The Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) provides us with a unique possibility of studying a dwarf galaxy merging event while still in progress. Due to its low distance (25 kpc), the main body of Sgr dSph covers a vast area in the sky (roughly 15 x 7 degrees). Available photometric and spectroscopic studies have concentrated either on the central part of the galaxy or on the stellar stream, but the overwhelming majority of the galaxy body has never been probed. The aim of the present study is twofold. On the one hand, to produce color magnitude diagrams across the extension of Sgr dSph to study its stellar populations, searching for age and/or composition gradients (or lack thereof). On the other hand, to derive spectroscopic low-resolution radial velocities for a subsample of stars to determine membership to Sgr dSph for the purpose of high resolution spectroscopic follow-up. We used VIMOS-VLT to produce V and I photometry and spectroscopy on 7 fields across the Sgr dSph minor and major axis, plus 3 more centered on the associated globular clusters Terzan 7, Terzan 8 and Arp 2. A last field has been centered on M 54, lying in the center of Sgr dSph. We present photometry for 320,000 stars across the main body of Sgr dSph, one of the richest, and safely the most wide-angle sampling ever produced for this fundamental object. We also provide robust memberships for more than one hundred stars, whose high resolution spectroscopic analysis will be the object of forthcoming papers. Sgr dSph appears remarkably uniform among the observed fields. We confirm the presence of a main Sgr dSph population characterized roughly by the same metallicity of 47 Tuc, but we also found the presence of multiple populations on the peripheral fields of the galaxy, with a metallicity spanning from [Fe/H]=-2.3 to a nearly solar value. Comment: 10 pages, 12 figures, accepted for publication in A&A

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    ABSTRACT: We use N-body simulations to explore the possibility that the Sagittarius (Sgr) dwarf galaxy was originally a late-type, rotating disc galaxy, rather than a non-rotating, pressure-supported dwarf spheroidal galaxy, as previously thought. We find that bifurcations in the leading tail of the Sgr stream, similar to those detected by the SDSS survey, naturally arise in models where the Sgr disc is misaligned with respect to the orbital plane. Moreover, we show that the internal rotation of the progenitor may strongly alter the location of the leading tail projected on the sky, and thus affect the constraints on the shape of the Milky Way dark matter halo that may be derived from modelling the Sgr stream. Our models provide a clear, easily tested prediction; although tidal mass stripping removes a large fraction of the original angular momentum in the progenitor dwarf galaxy, the remnant core should still rotate with a velocity amplitude ∼20 km s−1 that could be readily detected in future, wide-field kinematic surveys of the Sgr dwarf.
    Monthly Notices of the Royal Astronomical Society Letters 10/2010; 408(1):L26 - L30. · 5.52 Impact Factor
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    ABSTRACT: We trace the tidal Stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Red Clump stars from the catalog of the Sloan Digital Sky Survey - Data Release 6, in the range 150{\deg} < RA < 220{\deg}, corresponding to the range of orbital azimuth 220{\deg} < Lambda < 290{\deg}. Substructures along the line of sight are identified as significant peaks in the differential star count profiles (SCP) of candidate Red Clump stars. A proper modeling of the SCPs allows us to obtain: (a) <10% accurate, purely differential distances with respect to the main body of Sgr, (b) estimates of the FWHM along the line of sight, and (c) estimates of the local density, for each detected substructure. In the range 255{\deg} < Lambda < 290{\deg} we cleanly and continuously trace various coherent structures that can be ascribed to the Stream, in particular: the well known northern portion of the leading arm, running from d~43 kpc at Lambda ~ 290{\deg} to d ~ 30 kpc at Lambda ~ 255{\deg}, and a more nearby coherent series of detections lying at constant distance d ~ 25 kpc, that can be identified with a wrap of the trailing arm. The latter structure, predicted by several models of the disruption of Sgr dSph, was never traced before; comparison with existing models indicates that the difference in distance between these portions of the leading and trailing arms may provide a powerful tool to discriminate between theoretical models assuming different shapes of the Galactic potential. A further, more distant wrap in the same portion of the sky is detected only along a couple of lines of sight.[abridged] Comment: 31 pages, 28 figures, accepted for publication in the Astrophysical Journal, a version with figures at full resolution can be downloaded at the following URL:
    The Astrophysical Journal 07/2010; · 6.28 Impact Factor
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    ABSTRACT: Using VIMOS in imaging and spectroscopy modes and FLAMES spectroscopy data, we have mapped the Sagittarius dwarf spheroidal galaxy (Sgr dSph) photometrically and spectroscopically over eight fields along the galaxy minor and major axes. We have found, for the first time, striking evidence of multiple populations in the peripheral zones of this near companion of the Milky Way. These data, together with previous analyses of the Sgr dSph core and streams, supply a detailed picture of this galaxy, and will give us the opportunity to reconstruct the history of this object and its influence on the evolution of the Milky Way.
    The Messenger. 09/2010;

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