Two distinct ancient components in the Sculptor Dwarf Spheroidal Galaxy: First Results from DART

By E. Tolstoy, M. Irwin, A. Helmi, G. Battaglia, P. Jablonka, V. Hill, K. Venn, M. Shetrone, B. Letarte, A. Cole and 7 more. 2004

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We have found evidence for the presence of two distinct ancient stellar components (both ≥ 10 Gyr old) in the Sculptor dwarf spheroidal galaxy. We used the ESO Wide Field Imager (WFI) in conjunction with the VLT/FLAMES spec-trograph to study the properties of the resolved stellar population of Sculptor out to and beyond the tidal radius. We ﬁnd that two components are discernible in the spatial distribution of Horizontal Branch stars in our imaging, and in the [Fe/H] and v hel distributions for our large sample of spectroscopic measurements. They can be generally described as a “metal-poor” component ([Fe/H] < − 1 . 7) and a “metal-rich” component ([Fe/H] > − 1 . 7). The metal-poor stars are more spatially extended than the metal-rich stars, and they also appear to be kinematically distinct. These results provide an important insight into the formation processes of small systems in the early universe and the conditions found there. Even this simplest of galaxies appears to have had a surprisingly complex early evolution.

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Citations in the corpus

Resolving the Formation of Protogalaxies. III. Feedback from the First Stars (2007, background): “A subset of dwarf galaxies, dwarf spheroidals (dSph), have the highest mass-to-light ratios (de Blok & McGaugh 1997; Mateo 1998) and contain a population of metal-poor stars that are similar to Galactic halo stars (Tolstoy et al. 2004; Helmi et al. 2006).”
Redefining the Missing Satellites Problem (2007, background): “Some dSphs show evidence for multiple, dynamically distinct stellar populations, with each population described by its own surface density and velocity dispersion (Harbeck et al. 2001; Tolstoy et al. 2004; Westfall et al. 2006; McConnachie et al. 2006; Ibata et al. 2006).”
One Law to Rule Them All: The Radial Acceleration Relation of Galaxies (2016, background): “Some dSphs, however, show chemo-dynamically distinct stellar components (Tolstoy et al. 2004; Battaglia et al. 2006): one can distinguish between a metal-rich (MR) and a metal-poor (MP) component with the former more centrally concentrated and kinematically colder than the latter.”
Galaxy Masses: A Review (2013, methodology): “Mass modelling is feasible thanks to ambitious observational programs to measure the stellar kinematics of hundreds and sometimes several thousands of individual stars19 (Tolstoy et al. 2004; Lokas et al. 2005; Simon 19Similar methods apply to the study of Milky Way stars; see §4.”
The Cold Dark Matter Halos of Local Group Dwarf Spheroidals (2007, background): “…approximately flat out to the nominal tidal radius (see, e.g., Fornax, Walker et al. 2006a, Battaglia et al. 2006; Leo I, Koch et al. 2006; Sculptor, Tolstoy et al. 2004, Westfall et al. 2006; Leo II, Sohn et al. 2006; Sextans, Walker et al. 2006b; Carina, Muñoz et al. 2006; Draco and Ursa Minor,…”
Gaia DR2 proper motions of dwarf galaxies within 420 kpc (2018, background): “Are the metallicity gradients observed for several of the Milky Way “classical” dwarf spheroidal galaxies (e.g. Tolstoy et al. 2004; Battaglia et al. 2006, 2011) an intrinsic property of these systems or could interactions with the Milky Way have had a role in setting their presence or erasing them…”
The Observed Properties of Dark Matter on Small Spatial Scales (2007, background): “It can be shown, however, that younger and/ormoremetal-rich populations aremore centrally concentrated (e.g., Harbeck et al. 2001) and that these populations also tend to exhibit lower velocity dispersions (Tolstoy et al. 2004).”
The birth of a galaxy – II. The role of radiation pressure (2012, background): “…their [α/Fe] versus [Fe/H] evolution (Tolstoy, Hill & Tosi 2009), metallicity distribution functions (Kirby et al. 2011), metallicity radial gradients (Tolstoy et al. 2004), star formation histories (Monelli et al. 2010), and individual abundance patterns (Frebel et al. 2010; Caffau et al. 2011).”
MULTI-ELEMENT ABUNDANCE MEASUREMENTS FROM MEDIUM-RESOLUTION SPECTRA. III. METALLICITY DISTRIBUTIONS OF MILKY WAY DWARF SATELLITE GALAXIES (2010, background): “Tolstoy et al. (2004) recognized this possibility in their finding of two distinct kinematic and metallicity components in Sculptor.”
Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy (2005, unknown): “In addition, Tolstoy et al. (2004) have found evidence for two populations of ancient stars with differing metallicityandvelocity distributions within the Sculptor dSph.”
Analysis and calibration of CaII triplet spectroscopy of red giant branch stars from VLT/FLAMES observations (2007, methodology): “11 shows the CaT [Fe/H] derived from the T01 calibration (equation 14), which we used in Tolstoy et al. (2004), Battaglia et al. (2006) and Helmi et al. (2006).”
Axion dark matter, solitons and the cusp–core problem (2015, background): “They use the fact that some dSphs have been shown to have at least two stellar populations that are chemodynamically distinct (see e.g. Tolstoy et al. 2004; Battaglia et al. 2006, 2011).”