MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY

By J. D. de Jong, Brian Yanny, Hans-Walter Rix, A. Dolphin, N. Martin, Timothy C. Beers. 2009

171 citations recorded by the source corpus.

We map the stellar structure of the Galactic thick disk and halo by applying color–magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1 kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75 ± 0.07 kpc and 4.1 ± 0.4 kpc, respectively. We find a stellar halo flattening within ∼25 kpc of c/a = 0.88 ± 0.03 and a power-law index of 2.75 ± 0.07 (for 7 kpc ≲RGC ≲ 30 kpc). The model fits yield thick-disk and stellar halo densities at the solar location of ρthick,☉ = 10−2.3±0.1 M☉ pc−3 and ρhalo,☉ = 10−4.20±0.05 M☉ pc−3, averaging over any substructures. Our analysis provides the first clear in situ evidence for a radial metallicity gradient in the Milky Way's stellar halo: within R ≲ 15 kpc the stellar halo has a mean metallicity of [Fe/H] ≃ −1.6, which shifts to [Fe/H] ≃ −2.2 at larger radii, in line with the two-component halo deduced by Carollo et al. from a local kinematic analysis. Subtraction of the best-fit smooth and symmetric model from the overall density maps reveals a wealth of substructures at all latitudes, some attributable to known streams and overdensities, and some new. A simple warp cannot account for the low latitude substructure, as overdensities occur simultaneously above and below the Galactic plane.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/39a777705f1d107d11b235987645cc813052b654

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Citations in the corpus

The Milky Way’s stellar disk (2013, background): “…just as messy: the structure variously known as the ‘anticenter ring’, ‘Monoceros ring’, ‘Canis Major feature’ (Yanny et al. 2003; Martin et al. 2004; de Jong et al. 2010) reflects the fact that there are far more stars at RGC = 15 to 20 kpc (Conn et al. 2012) with |z| > 1 kpc than a simple…”
METALLICITY GRADIENTS IN THE MILKY WAY DISK AS OBSERVED BY THE SEGUE SURVEY (2011, methodology): “One way to quantify the amount of contamination is by examining different multicomponent models for the Galaxy, in particular, those of Jurić et al. (2008) and de Jong et al. (2010).”
Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “…component, but contains substructure resulting from accretion events, superimposed on a dichotomy of inner and outer components (Hartwick 1987, Norris & Ryan 1989, Carollo et al. 2007, 2010, 2014, de Jong et al. 2010, Deason, Belokurov & Evans 2011, Beers et al. 2012, and references therein).”
Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, background): “However, recent results based on SDSS observations suggest suggest a similar drop of ≈ 0.7 − 0.8 dex from the Solar 8 Where appropriate we have adjusted the observational metallicity measurements (by applying a constant offset) to account for differences in the assumed solar abundances in the studie”
THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I. HUBBLE SPACE TELESCOPE/WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS (2014, methodology): “…we generated synthetic CMDs using the Dartmouth stellar evolution libraries (Dotter et al. 2008) and the Milky Way structural model presented in de Jong et al. (2010), and allowed MATCH to linearly scale the resulting CMD to model any putative foreground stars that may have contaminated each CMD.”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “…000) of faint and more distant stars such as the Sloan Extension for Galactic Understanding and Exploration (SEGUE/SDSS, e.g., Yanny et al. 2009; de Jong et al. 2010; Lee et al. 2011; Cheng et al. 2012a,b; Schlesinger et al. 2012) are improving significantly our knowledge of Galactic structure,…”
Constraining the thick disc formation scenario of the Milky Way (2014, unknown): “…us to have a more physical law, derivable in the plane, which is useful in dealing with dynamical computation; the exponential shows a singular point in the derivative at z=0. de Jong et al. (2010) attempted to fit the SEGUE imaging survey with a smooth model with a thick disc and a stellar halo.”
KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS (2012, background): “Carollo et al. (2010) and de Jong et al. (2010) have found that the population fraction inversion point between the inner and outer halo lies between∼ 15− 20 kpc. Kinman et al. (2012) studied the BHB and RR Lyrae stars towards the galactic-anticenter and North Galactic Pole and found that the…”
THE CASE FOR THE DUAL HALO OF THE MILKY WAY (2011, methodology): “In their analysis of these data, de Jong et al. (2010) employed a CMD fitting approach, based on templates of old stellar populations with differing metallicities, to obtain a sparse three-dimensional map of the stellar distribution at |Z| > 1 kpc.”
KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD, (2012, background): “…Cabrera-Lavers et al. (2005); Girard et al. (2006); Vallenari et al. (2006); Brown et al. (2008); Cabrera-Lavers et al. (2007); Arnatoddir et al. (2008); Bilir et al. (2008); Jurić et al. (2008); Veltz et al. (2008); de Jong et al. (2010); Just et al. (2011); Chang et al. (2011) of Figure 1.”
Radial migration in disc galaxies — I. Transient spiral structure and dynamics (2011, methodology): “Studies using datafrom the SDSS (e.g. Jurić et al. 2008; Ivezić et al. 2008) and itsfollowup surveys such as SEGUE (Yanny et al. 2009; de Jong et al. 2010; Lee et al. 2011), as well as results using data from RAVE (Wilson et al. 2011; Ruchti et al. 2011) have already pushed the current models to…”