A FIRST CONSTRAINT ON THE THICK DISK SCALE LENGTH: DIFFERENTIAL RADIAL ABUNDANCES IN K GIANTS AT GALACTOCENTRIC RADII 4, 8, AND 12 kpc

By T. Bensby, A. Alves-Brito, M. Oey, David Yong, Jorge Meléndez. 2011

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Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes, we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at Galactocentric distances between 9 and 13 kpc. The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighborhood, analyzed using identical methods. For Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighborhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. We make a first estimate of the thick disk scale length of Lthick = 2.0 kpc, assuming Lthin = 3.8 kpc for the thin disk. We suggest that radial migration may explain the lack of radial age, metallicity, and abundance gradients in the thick disk, possibly also explaining the link between the thick disk and the metal-poor bulge.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ee9f7c9ff8a4a0324f48a301b78944f7fd064788

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Citations in the corpus

The Milky Way’s stellar disk (2013, background): “…particular, many studies have explicitly included kinematical pre-selections of the target stars (e.g., Bensby et al. 2003; Feltzing & Bensby 2008; Bensby et al. 2011); others, e.g. Navarro et al. (2011), are foremost literature compilations without quantitative accounting for the selection…”
THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK (2011, background): “…α-old sample is dominated by a population of stars with a scale height of 686±11 pc, and a short scale length of 2.01±0.05 kpc (consistent with the rough estimate of 2 kpc based on a handful of stars by Bensby et al. 2011 and the indirect dynamical estimate of 2.2±0.35 kpc of Carollo et al. 2010).”
The Gaia-ESO Survey : radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk (2014, result): “These results are very interesting, and they support and extend the results of the earlier studies, including Bensby et al. (2010, 2011) and Bovy et al. (2012c).”
Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood (2013, methodology): “In Bensby et al. (2011b) the lack ofα-enhanced stars in the outer disk, even if they were located far (> 1 kpc) from the plane, was interpreted as being due to the fact that the thick disk had a much shorter scale-length than the thin disk.”
Chemodynamical evolution of the Milky Way disk II: Variations with Galactic radius and height above the disk plane (2014, background): “Several studies of the [Fe/H]-[α/Fe] plane (e.g., Bensby et al. 2011; Cheng et al. 2012a; Anders et al. 2014) have shown that the number of high-[α/Fe] metal-poor stars d creases strongly in the outer disk.”
The GALAH survey and Gaia DR2: dissecting the stellar disc’s phase space by age, action, chemistry, and location (2018, background): “Bensby et al. (2011) first suggested a shorter scale length for the α-rich disc compared to the dominant α-poor disc that was confirmed by the APOGEE survey (Bovy 2015; Hayden et al. 2015).”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, background): “This indicates that the chemical properties of the thick disc population is radially well mixed (see also Bensby et al. 2011; Nidever et al. 2014), while the thin disc population preserves their radial and vertical metallicity gradient well.”
CHEMICAL CARTOGRAPHY WITH APOGEE: LARGE-SCALE MEAN METALLICITY MAPS OF THE MILKY WAY DISK (2013, methodology): “[α/M] Subsamples As a first cut at separating the sample by age, we adopt [α/M] as a potential age discriminator (Lee et al. 2011; Bensby et al. 2011; Cheng et al. 2012a; Bovy et al. 2012a,b,c), where stars with higher [α/M] are more likely to be older stars.”
CHEMICAL CARTOGRAPHY WITH APOGEE: METALLICITY DISTRIBUTION FUNCTIONS AND THE CHEMICAL STRUCTURE OF THE MILKY WAY DISK (2015, background): “…andhave shorter radial scalelengths, larger vertical scale heights, and hotter kinematics than most stars in the solar neighborhood (e.g., Bensby et al. 2003, 2011; Allende Prieto et al. 2006; Bovy et al. 2012c; Cheng et al. 2012a; Anders et al. 2014), although there do exist thick-disk…”
A DIRECT DYNAMICAL MEASUREMENT OF THE MILKY WAY'S DISK SURFACE DENSITY PROFILE, DISK SCALE LENGTH, AND DARK MATTER PROFILE AT 4 kpc ≲ R ≲ 9 kpc (2013, background): “…disk contains abundance-distinct subcomponents with scale lengths ranging from 2 kpc to > 4.5 kpc (Bovy et al. 2012d), and in particular that the thicker disk components in the Milky Way have a much shorter scale length than the thin disk (Bensby et al. 2011; Bovy et al. 2012d; Cheng et al. 2012).”
THE MILKY WAY HAS NO DISTINCT THICK DISK (2011, background): “…the structural parameters (e.g., the radial scale lengths) for the thicker and thinner components, when they are based on an elemental-abundance selection of sample stars (Bensby et al. 2011; Bovy et al. 2011, B11 hereafter), as opposed to luminosity- or volume-selection (e.g., Jurić et al. 2008).”
The effects of radial migration on the vertical structure of Galactic discs (2012, background): “These findings are consistet with Bensby et al. (2011) who also found a short scale-lengthfor targeted thick-disc stars using entirely different data.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “Bensby et al. (2011) estimate an exponential scale length of 2 kpc (≈10% accuracy), in good agreement with the high-[α/Fe] MAPs from SEGUE (Bovy et al. 2012c), although Cheng et al. (2012) measure RT ≈ 1.8 kpc using 7,000 MSTO dwarfs from the same survey, albeit with larger errors.”
Constraining the thick disc formation scenario of the Milky Way (2014, unknown): “We are also consistent with Bensby et al. (2011), who evaluated the scale length to be 2 kpc, but with samples very limited in size and without estimating of the error bar, although it is not sure that the two methods trace exactly the same population.”
THE RELATIONSHIP BETWEEN MONO-ABUNDANCE AND MONO-AGE STELLAR POPULATIONS IN THE MILKY WAY DISK (2016, background): “Such a scenario explains why chemically- or age-defined thick disks are centrally concentrated (Bensby et al. 2011; Bovy et al. 2012), but geometrically thick populations in both observations of external edge-on galaxies (Yoachim and Dalcanton 2006; Pohlen et al. 2007; Comerón et al. 2012) and in…”
THE STELLAR POPULATION STRUCTURE OF THE GALACTIC DISK (2015, methodology): “The second approach, Galactic archaeology, aims at obtaining detailed observations of local galaxies, either through resolving their stellar popula- 1 Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4, Canada; bovy@astro.utoronto.ca 2 Institu”
Chemodynamics of the Milky Way - I. The first year of APOGEE data (2013, background): “Using our large sample of red giants stars, we corroborate the results obtained by Bensby et al. (2011); Bovy et al. (2012c) and Cheng et al. (2012b) who found evidence for a shorter scale-length of the thick disc.”