Radial mixing and the transition between the thick and thin Galactic discs

By M. Haywood. 2008

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The analysis of the kinematics of solar neighbourhood stars shows that the low- and high-metallicity tails of the thin disc are populated by objects which orbital properties suggest an origin in the outer and inner Galactic disc, respectively. Signatures of radial migration are identified in various recent samples, and are shown to be responsible for the high-metallicity dispersion in the age–metallicity distribution. Most importantly, it is shown that the population of low-metallicity wanderers of the thin disc (−0.7 < [Fe/H] < −0.3 dex) is also responsible for the apparent hiatus in metallicity with the thick disc (which terminal metallicity is about −0.2 dex). It implies that the thin disc at the solar circle has started to form stars at about this same metallicity. This is also consistent with the fact that ‘transition’ objects, which have α-element abundance intermediate between that of the thick and thin discs, are found in the range [−0.4, −0.2] dex. Once the metal-poor thin disc stars are recognized for what they are – wanderers from the outer thin disc – the parenthood between the two discs can be identified on stars genuinely formed at the solar circle through an evolutionary sequence in [α/Fe] and [Fe/H]. Another consequence is that stars that can be considered as truly resulting of the chemical evolution at the solar circle have a metallicity restricted to about [−0.2, +0.2] dex, confirming an old idea that most chemical evolution in the Milky Way have preceded the thin disc formation.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “Haywood (2008) suggested that the trend between [Fe/H] and Vφ, or simply the metallicity-velocity relation (MVR), can serve as a test for the contamination from migration in the solar neighborhood.”
THE EFFECT OF RADIAL MIGRATION ON GALACTIC DISKS (2014, background): “As discussed, for example, by Haywood (2008), this might explain the puzzling anti-correlation between metallicity and rotation velocity found for stars in the thin disk.”
Through thick and thin: kinematic and chemical components in the solar neighbourhood (2010, background): “…papers, which argue that the chemo-dynamical evidence for accretion events is weak and that all relevant data can be explained by reconsidering the importance of radial migration of both gas and stars during the evolution of the disk (Haywood 2008; Roškar et al. 2008; Schönrich & Binney 2009a).”
THE GENESIS OF THE MILKY WAY'S THICK DISK VIA STELLAR MIGRATION (2010, background): “This is consistent with the arguments put forth by Haywood (2008) as observational evidence of radial mixing.”
Chemical evolution with radial mixing (2008, background): “1(b) of Haywood (2008) is satisfyingly similar to the lower panel of our Fig.”
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program - Galactic stellar populations and planets (2012, methodology): “…et al. 2011), metal-poor and α-enhanced (Fuhrmann 1998; Prochaska et al. 2000; Feltzing et al. 2003; Mishenina et al. 2004; Reddy et al. 2006; Haywood 2008b, Lee et al. 2011) stars that move in Galactic orbits with a large-scale height and long-scale length (Robin et al. 1996; Buser et al.…”
Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances (2014, background): “The metal-poor stars are characterised by having a tendency to travel along their orbit faster than the local standard of rest (LSR), as shown in Haywood (2008) – whereas the thick disk, at the same metallicities, lags the LSR.”
New constraints on the chemical evolution of the solar neighbourhood and galactic disc(s) - improved astrophysical parameters for the Geneva-Copenhagen Survey (2011, background): “Our analysis thus clearly confirms a similar result drawn by Haywood (2008) from a smaller spectroscopic sample.”
ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way (2012, background): “We know from the age-metallicity relation in the solar neighbourhood (e.g. Haywood 2008) that the chemical evolution of the solar neighbourhood proceeded rapidly: 10 Gyrago, the stars of the thin disk in the solar neighbourhood alreadyhad a mean [Fe/H] near solar, with a spread from about+0.5 to…”
Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts (2012, background): “In the MW, small satellites on radial, in-plane orbits can cause mixing in the outer disc (Quillen et al., 2009) and thus account for the fraction of low-metallicity stars present in the solar neighborhood (Haywood, 2008).”
Gaia Universe model snapshot - A statistical analysis of the expected contents of the Gaia catalogue (2012, methodology): “Contrarily to Robin et al. (2003) metallicities [Fe/H] are computed through an empirical age-metallicity relation ψ (Z,Age) from Haywood (2008).”
INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS (2013, background): “…potential role of radial migration as a mechanism to redistribute stars and diversify the distribution of stellar chemical composition as a function of radius (e.g., Sellwood & Binney 2002; Haywood 2008; Roškar et al. 2008a; Schönrich & Binney 2009a; Casagrande et al. 2011; Minchev et al. 2012b).”
FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [α/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE (2011, background): “Thus, there should exist a gradient in the variation of rotationalvelocity with metallicity; evidence for such a behavior has been claimed observationally by Haywood (2008).”
Measuring Radial Orbit Migration in the Galactic Disk (2018, background): “…remarkable, longstanding observations that there is no distinct age–metallicity relation of stars in the solar neighborhood (a few hundred parsecs around the Sun), and that there is a wide spread of metallicities at the solar radius (Edvardsson et al. 1993; Haywood 2008; Casagrande et al. 2011).”
Riding the Spiral Waves: Implications of Stellar Migration for the Properties of Galactic Disks (2008, methodology): “…designed to reproduce Milky Way observables, they successfully reproduce the major qualitative features of the observations: the observed AMR is indeed relatively flat with a high degree of scatter (Edvardsson et al. 1993; Nordström et al. 2004), which gradually increases with age (Haywood 2008).”
The lifetimes of spiral patterns in disc galaxies (2010, result): “However, there seems to be general agreement that there is a spread of metallicities at each age, which is also supported by other studies (Chen et al. 2003; Haywood 2008; Stanghellini & Haywood 2010).”
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient (2018, background): “Haywood (2008) argued that stars with low-[α/Fe] and low-metallicity were born in the outer disk.”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “This was demonstrated in Haywood (2008) for stars in the solar vicinity, and is also clearly visible in Fig.”
THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK (2011, background): “…& Dalcanton 2005), and metal-poor (compared to the thin-disk components), as well as enhanced in α-elements (Fuhrmann 1998; Prochaska et al. 2000; Tautvaǐsienė et al. 2001; Bensby et al. 2003; Feltzing et al. 2003; Mishenina et al. 2004; Bensby et al. 2005; Reddy et al. 2006; Haywood 2008).”