METALLICITY GRADIENTS IN THE MILKY WAY DISK AS OBSERVED BY THE SEGUE SURVEY

By Judy Y. Cheng, C. Rockosi, H. Morrison, R. Schönrich, Y. S. Lee, Timothy C. Beers, D. Bizyaev, K. Pan, D. Schneider. 2011

117 citations recorded by the source corpus.

The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides a powerful constraint on the chemical enrichment and dynamical history of the disk system. We present the radial metallicity gradient, Δ[Fe/H]/ΔR, as a function of height above the plane, |Z|, using 7010 main-sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 kpc < R < 16 kpc, 0.15 kpc < |Z| < 1.5 kpc. The data reveal that the radial metallicity gradient becomes flat at heights |Z| > 1 kpc. The median metallicity at large |Z| is consistent with the metallicities seen in outer disk open clusters, which exhibit a flat radial gradient at [Fe/H] ∼−0.5. We note that the outer disk clusters are also located at large |Z|; because the flat gradient extends to small R for our sample, there is some ambiguity in whether the observed trends for clusters are due to a change in R or |Z|. We therefore stress the importance of considering both the radial and vertical directions when measuring spatial abundance trends in the disk. The flattening of the gradient at high |Z| also has implications on thick disk formation scenarios, which predict different metallicity patterns in the thick disk. A flat gradient, such as we observe, is predicted by a turbulent disk at high redshift, but may also be consistent with radial migration, as long as mixing is strong. We test our analysis methods using a mock catalog based on the model of Schönrich & Binney, and we estimate our distance errors to be ∼25%. We also show that we can properly correct for selection biases by assigning weights to our targets.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “…negative) for samples at increasingly larger distance from the disk midplane, |z|, has been observed in most large Milky Way surveys (e.g., SEGUE - Cheng et al. 2012, RAVE - Boeche et al. 2013b, APOGEE - Anders et al. 2014, Gaia-ESO - Recio-Blanco et al. 2014, LAMOST - Wang et al. 2019),…”
Chemodynamical evolution of the Milky Way disk II: Variations with Galactic radius and height above the disk plane (2014, methodology): “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.”
CHEMICAL CARTOGRAPHY WITH APOGEE: LARGE-SCALE MEAN METALLICITY MAPS OF THE MILKY WAY DISK (2013, methodology): “…Carrera & Pancino 2011; Frinchaboy et al. 2013), B stars (e.g., Daflon & Cunha 2004; Daflon et al. 2009), and surveys of main sequence stars (e.g., Cheng et al. 2012b for the Sloan Extension for Galactic Understanding and Exploration [SEGUE; Yanny et al. 2009] of the Sloan Digital Sky Survey…”
CHEMICAL CARTOGRAPHY WITH APOGEE: METALLICITY DISTRIBUTION FUNCTIONS AND THE CHEMICAL STRUCTURE OF THE MILKY WAY DISK (2015, background): “…the disk of the Galaxy, such as the thick disk (e.g., Yoshii 1982; Gilmore & Reid 1983), chemical abundance gradients (e.g., Hartkopf & Yoss 1982; Cheng et al. 2012b; Anders et al. 2014; Hayden et al. 2014; Schlesinger et al. 2014), and the G-dwarf problem (van den Bergh 1962; Pagel & Patchett…”
The age–metallicity structure of the Milky Way disc using APOGEE (2017, background): “…in the choice of definition of the measured population between a geometric or chemical abundance selection, with many studies finding a scale length for the abundance-selected α-rich disk in the range hR = 2.0 ± 0.2 kpc (Bland-Hawthorn & Gerhard 2016; Bovy et al. 2016b, 2012b; Cheng et al. 2012b).”
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.”
PLATO as it is: a legacy mission for Galactic archaeology (2017, unknown): “…of these two relations are reflected in the chemical abundance gradients in the disk (e.g., Anders et al. 2014, 2017a; Boeche et al. 2013, 2014; Cheng et al. 2012; Hayden et al. 2014; Jacobson et al. 2016; Mikolaitis et al. 2014), as well as on variations of metallicities and abundance ratios…”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “Indeed, the α-rich thick disk is centrally concentrated with a short scale length of about 2 kpc (Bensby et al. 2011; Bovy et al. 2012, 2016; Cheng et al. 2012b), and very few α-rich stars are found in the outer disk of the Milky Way (Nidever et al. 2014; Hayden et al. 2015).”
On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk (2014, methodology): “For seven OCs selected by Cheng et al. (2012) we adopted the parameters given by WEBDA and for PWM4 the estimates p ovided by Yong et al. (2012).”
THE VERTICAL METALLICITY GRADIENT OF THE MILKY WAY DISK: TRANSITIONS IN [α/Fe] POPULATIONS (2014, methodology): “Cheng et al. (2012a) measured radial metallicity gradients for an unbiased low-latitude sample of SEGUE main-sequence turnoff stars, ranging from 6 to 16 kpc in Galactocentric radius.”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, background): “Negative metallicity gradient are widely observed in the canonical thin disk both in small samples (e.g. Genovali et al. 2014) and large surveys (e.g. Cheng et al. 2012; Mikolaitis et al. 2014).”
INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS (2013, background): “Stars far from the plane (|z| > 1 kpc) have similar [Fe/H] over a broad range in radius (Cheng et al. 2012a), suggesting that these stars may share a temporal origin.”
THE METALLICITY DISTRIBUTION FUNCTIONS OF SEGUE G AND K DWARFS: CONSTRAINTS FOR DISK CHEMICAL EVOLUTION AND FORMATION (2011, methodology): “To constrain these effects, we simulate the distribution of reddening values at a range of extinctions, using the main-sequence turnoff stars from Cheng et al. (2012), on TRILEGAL Galaxy models along each SEGUE line of sight.”
The GALAH survey: scientific motivation (2015, background): “The Galactic thin disc shows a mean radial metallicity gradient of about −0.07 dex kpc−1 (e.g. Cheng et al. 2012).”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “…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, dynamics, and chemistry, thus…”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “Moreover, a tight age–metallicity relation as found here, combined with an inside-out scenario, should produce a radial metallicity, or [α/Fe], gradient in the thick disk, which is not observed (Cheng et al. 2012b).”
Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s) (2017, background): “The running mean of Rguide shows a gentle decline with age for the full sample while revealing an average lower value for the high-α stars than for the low-α population (see also Reddy et al. 2003; Bensby et al. 2011; Bovy et al. 2012; Cheng et al. 2012; Allende Prieto et al. 2016).”
TRACING CHEMICAL EVOLUTION OVER THE EXTENT OF THE MILKY WAY'S DISK WITH APOGEE RED CLUMP STARS (2014, methodology): “In particular, it has become clear that high-α stars have a shorter radial scale length than stars with solar [α/Fe] (Bensby et al. 2011a; Bovy et al. 2012b; Cheng et al. 2012; Anders et al. 2014).”