THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK

By Jo Bovy, Hans-Walter Rix, Chao Liu, David W. Hogg, Timothy C. Beers, Y. S. Lee. 2011

292 citations recorded by the source corpus.

The spatial, kinematic, and elemental-abundance structure of the Milky Way's stellar disk is complex, and has been difficult to dissect with local spectroscopic or global photometric data. Here, we develop and apply a rigorous density modeling approach for Galactic spectroscopic surveys that enables investigation of the global spatial structure of stellar sub-populations in narrow bins of [α/Fe] and [Fe/H], using 23,767 G-type dwarfs from SDSS/SEGUE, which effectively sample 5 kpc < RGC < 12 kpc and 0.3 kpc ≲ |Z| ≲ 3 kpc. We fit models for the number density of each such ([α/Fe] and [Fe/H]) mono-abundance component, properly accounting for the complex spectroscopic SEGUE sampling of the underlying stellar population, as well as for the metallicity and color distributions of the samples. We find that each mono-abundance sub-population has a simple spatial structure that can be described by a single exponential in both the vertical and radial directions, with continuously increasing scale heights (≈200 pc to 1 kpc) and decreasing scale lengths (>4.5 kpc to 2 kpc) for increasingly older sub-populations, as indicated by their lower metallicities and [α/Fe] enhancements. That the abundance-selected sub-components with the largest scale heights have the shortest scale lengths is in sharp contrast with purely geometric “thick–thin disk” decompositions. To the extent that [α/Fe] is an adequate proxy for age, our results directly show that older disk sub-populations are more centrally concentrated, which implies inside-out formation of galactic disks. The fact that the largest scale-height sub-components are most centrally concentrated in the Milky Way is an almost inevitable consequence of explaining the vertical structure of the disk through internal evolution. Whether the simple spatial structure of the mono-abundance sub-components and the striking correlations between age, scale length, and scale height can be plausibly explained by satellite accretion or other external heating remains to be seen.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/46dbbaab96f26c31fe14295c75a50345713a36e9

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Citations in the corpus

A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “…2003; Adibekyan et al. 2012; Haywood et al. 2013); (3) chemically, as the α-rich sequence in the [α/Fe] versus [Fe/H] plane (Fuhrmann 1998; Navarro et al. 2011; Adibekyan et al. 2012; Bovy et al. 2012); (4) as the old part of the disk (Haywood et al. 2013; Bensby et al. 2014; Xiang et al. 2015).”
The origin of accreted stellar halo populations in the Milky Way using APOGEE,Gaia, and the EAGLE simulations (2018, methodology): “…mergers, which would produce a plateau in the age or α abundance against scale height relationship that is not currently borne out by the data (e.g. Bovy et al. 2012a,b,c, 2016; Casagrande et al. 2016; Mackereth et al. 2017) 2 The recent paper by Fernández-Alvar et al. (2018a) hints at a similar…”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, background): “It is defined spatially by an exponential power law with a larger vertical scale height and smaller radial scale length compared to the thin disk (e.g. Bovy et al. 2012; Haywood et al. 2013).”
THE RELATIONSHIP BETWEEN MONO-ABUNDANCE AND MONO-AGE STELLAR POPULATIONS IN THE MILKY WAY DISK (2016, background): “11 by MCM14, where it was already noted that the lack of good fit by single exponential profiles for low[α/Fe] high-[Fe/H] stars was in contrast to the results of Bovy et al. (2012) using the SEGUE G-dwarf sample.”
CHEMICAL CARTOGRAPHY WITH APOGEE: LARGE-SCALE MEAN METALLICITY MAPS OF THE MILKY WAY DISK (2013, methodology): “The nature of the vertical structure continues to be debated, with some studies suggesting that the thin and thick-disks are distinct populations, while others report that there is just a single component with a continuous distribution of properties (e.g., Ivezic et al. 2008; Bovy et al. 2012a,b,c).”
STARS, GAS, AND DARK MATTER IN THE SOLAR NEIGHBORHOOD (2015, methodology): “This is marginally consistent with the result of Bovy et al. (2012b), who found M30 1 pc 2 - .”
Chemodynamical evolution of the Milky Way disk II: Variations with Galactic radius and height above the disk plane (2014, methodology): “The overall decrease of high-[Mg/Fe] stars in the outer disk is consistent with the results of recent observational studies (e.g., Bensby et al. 2011; Anders et al. 2014; Bovy et al. 2012b), which have shown that the chemically defined Milky Way thick disk is more centrally concentrated than the thi”
ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, background): “By fitting exponential disks to mono-abundance populations Bovy et al. (2012) finds scale lengths to be roughly in range 2−4.5 kpc and scale heights to be roughly in range 0.2−1 kpc.”
THE APOGEE RED-CLUMP CATALOG: PRECISE DISTANCES, VELOCITIES, AND HIGH-RESOLUTION ELEMENTAL ABUNDANCES OVER A LARGE AREA OF THE MILKY WAY'S DISK (2014, methodology): “…a scale ∆R across an azimuthal range ∆φ near the Sun would disappear in approximately few×Tφ×(∆φ/360 ◦)× ( R0/max(∆R, σRg ) ) , where Tφ is the rotational period (≈ 250Myr) and σRg is the spread in guiding-star radii (≈ 0.1R near R0 or about 1 kpc for the intermediate-age disk; Bovy et al. 2012a).”
The Milky Way’s stellar disk (2013, methodology): “In particular for σz , which Bovy et al. (2012c) have investigated in detail, the degree of isothermally is remarkable (see Fig.”
MEASUREMENT OF THE RADIUS OF NEUTRON STARS WITH HIGH SIGNAL-TO-NOISE QUIESCENT LOW-MASS X-RAY BINARIES IN GLOBULAR CLUSTERS (2012, methodology): “Other analyses have used the Stretch-Move algorithm (Bovy et al. 2012; Olofsson et al. 2012, using another implementation, by Foreman-Mackey et al. 2012).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “The GCS survey covers the full sky but is confined to the Solar Neighborhood; the SEGUE, RAVE, and APOGEE surveys penetrate deeper into the Galaxy than earlier stellar surveys.”
TRACING CHEMICAL EVOLUTION OVER THE EXTENT OF THE MILKY WAY'S DISK WITH APOGEE RED CLUMP STARS (2014, methodology): “Our α-element abundance distribution shows some differences compared to the medium-resolution SEGUE Gdwarf sample of Lee et al. (2011) and Bovy et al. (2012b), especially in the distinct bimodality at the metal-poor end.”
Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances (2014, background): “These stars have been characterised on larger orbits, see Bovy et al. (2012), figure 7, which shows that these objects have average guiding centers larger than the solar radius (Rmean > 9 kpc).”
Chemodynamics of the Milky Way - I. The first year of APOGEE data (2013, methodology): “…al. 2013b), or – Due to yet another selection effect related to the inhomogeneous coverage of the Galactic disc(s) by finite-sightline observations (Bovy et al. 2012c), which is present in all the currently available large-scale Galactic survey data (APOGEE, 22 Rg ≈ Rmed is the orbital »guiding…”
Constraining the Galaxy's dark halo with RAVE stars (2014, background): “The low-latitude infrared survey APOGEE (Allende Prieto et al. 2008) should resolve this issue, but to date it has not yielded physically plausible results (Bovy et al. 2012b).”