Probing the Galactic thick disc vertical properties and interfaces

Katz, David; Soubiran, C.; Cayrel, Roger; Barbuy, B.; Friel, Eileen D.; Bienaymé, O.; Perrin, M. N.

doi:10.1051/0004-6361/201014840

Cited by 63 publications

(91 citation statements)

References 68 publications

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“…The solid black lines in each panel display the total number of stars in the annulus 7 < r < 9 kpc. A negative trend is seen for both |z| and |v z | as expected from observations (e.g., Katz et al 2011;Schlesinger et al 2012;Rix & Bovy 2013). As in the |z|−σ z relation, we find a flattening at |z| 2 kpc for |z|−[Fe/H], as well as in the |v z |−[Fe/H] relation at |v z | 90 km s −1 .…”

Section: Vertical Structure Of the Local Disksupporting

confidence: 87%

Chemodynamical evolution of the Milky Way disk

Minchev

Chiappini

Martig

2013

A&A

443

574

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In the first paper of this series, we present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks. This method avoids known star formation and chemical enrichment problems encountered in simulations. Here we focus on the Milky Way, by using a detailed thindisk chemical evolution model (matching local observables, which are weakly affected by radial migration) and a simulation in the cosmological context, with dynamical properties close to those of our Galaxy. We examine in detail the interplay between in situ chemical enrichment and radial migration and their impact on key observables in the solar neighborhood, e.g., the age-metallicityvelocity relation, the metallicity distribution, and gradients in the radial and vertical directions. We show that, due to radial migration from mergers at high redshift and the central bar at later times, a sizable fraction of old metal-poor high-[α/Fe] stars can reach the solar vicinity. This naturally accounts for a number of recent observations related to both the thin and thick disks, despite the fact that we use thin-disk chemistry only. Although significant radial mixing is present, the slope in the age-metallicity relation is only weakly affected, with a scatter compatible with recent observational work. While we find a smooth density distribution in the [O/Fe]-[Fe/H] plane, we can recover the observed discontinuity by selecting particles according to kinematic criteria used in high-resolution samples to define the thin and thick disks. We outline a new method for estimating the birth place of the Sun and predict that the most likely radius lies in the range 4.4 < r < 7.7 kpc (for a current location at r = 8 kpc). A new, unifying model for the Milky Way thick disk is offered, where both mergers and radial migration play a role at different stages of the disk evolution. We show that in the absence of early-on massive mergers the vertical velocity dispersion of the oldest stars is underestimated by a factor of ∼2 compared with observations. We can, therefore, argue that the Milky Way thick disk is unlikely to have been formed through a quiescent disk evolution. An observational test involving both chemical and kinematic information must be devised to ascertain this possibility.

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Section: Vertical Structure Of the Local Disksupporting

confidence: 87%

Chemodynamical evolution of the Milky Way disk

Minchev

Chiappini

Martig

2013

A&A

443

574

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“…A thick-disc mean metallicity of ∼−0.5 dex was found by some authors Kordopatis et al 2011b;Schlesinger et al 2012;Soubiran et al 2003) with a gradient that decreases the mean metallicity ∼−0.8 dex beyond 3 kpc (Katz et al 2011;Ivezić et al 2008). The lack of a prominent low-metallicity tail in the RAVE and GCS samples compared with the mock sample supports these studies.…”

Section: Abundance Gradients In the Galaxia/besançon Mock Samplesupporting

confidence: 71%

Chemical gradients in the Milky Way from the RAVE data

Boeche

Siebert

Piffl

et al. 2013

A&A

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Aims. We aim at measuring the chemical gradients of the elements Mg, Al, Si, and Fe along the Galactic radius to provide new constraints on the chemical evolution models of the Galaxy and Galaxy models such as the Besançon model. Thanks to the large number of stars of our RAVE sample we can study how the gradients vary as function of the distance from the Galactic plane. Methods. We analysed three different samples selected from three independent datasets: a sample of 19 962 dwarf stars selected from the RAVE database, a sample of 10 616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS) dataset, and a mock sample (equivalent to the RAVE sample) created by using the GALAXIA code, which is based on the Besançon model. The three samples were analysed by using the very same method for comparison purposes. We integrated the Galactic orbits and obtained the guiding radii (R g ) and the maximum distances from the Galactic plane reached by the stars along their orbits (Z max ). We measured the chemical gradients as functions of R g at different Z max . Results. We found that the chemical gradients of the RAVE and GCS samples are negative and show consistent trends, although they are not equal: at Z max < 0.4 kpc and 4.5 < R g (kpc) < 9.5, the iron gradient for the RAVE sample is d[Fe/H]/dR g = −0.065 dex kpc −1 , whereas for the GCS sample it is d[Fe/H]/dR g = −0.043 dex kpc −1 with internal errors of ±0.002 and ±0.004 dex kpc −1 , respectively. The gradients of the RAVE and GCS samples become flatter at larger Z max . Conversely, the mock sample has a positive iron gradient of d[Fe/H]/dR g = +0.053 ± 0.003 dex kpc −1 at Z max < 0.4 kpc and remains positive at any Z max . These positive and unrealistic values originate from the lack of correlation between metallicity and tangential velocity in the Besançon model. In addition, the low metallicity and asymmetric drift of the thick disc causes a shift of the stars towards lower R g and metallicity which, together with the thin-disc stars with a higher metallicity and R g , generates a fictitious positive gradient of the full sample. The flatter gradient at larger Z max found in the RAVE and the GCS samples may therefore be due to the superposition of thin-and thick-disc stars, which mimicks a flatter or positive gradient. This does not exclude the possibility that the thick disc has no chemical gradient. The discrepancies between the observational samples and the mock sample can be reduced by i) decreasing the density; ii) decreasing the vertical velocity; and iii) increasing the metallicity of the thick disc in the Besançon model.

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“…Soubiran, Bienaymé & Siebert (2003) introduced this concept to determine the atmospheric parameters and absolute magnitude of a star by computing a likelihood function of the difference between its spectrum and a grid of observed spectra of stars with parallaxes. The reported distances errors are less than 30% for when compared with Hipparcos parallaxes of FGK stars (Katz et al 2011) and less than 12% when red clump stars are considered (Soubiran et al 2008). This compares well with other methods but in this case the distances rely on interpolations in the parameter space to compute the likelihood function and not on stellar evolution and atmosphere models.…”

Section: Introductionsupporting

confidence: 56%

Climbing the cosmic ladder with stellar twins

Jofré

Mädler

Gilmore

et al. 2015

Mon. Not. R. Astron. Soc.

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Distances to stars are key to revealing a three-dimensional view of the Milky Way, yet their determination is a major challenge in astronomy. Whilst the brightest nearby stars benefit from direct parallax measurements, fainter stars are subject of indirect determinations with uncertainties exceeding 30%. We present an alternative approach to measuring distances using spectroscopically-identified twin stars. Given a star with known parallax, the distance to its twin is assumed to be directly related to the difference in their apparent magnitudes. We found 175 twin pairs from the ESO public HARPS archives and report excellent agreement with Hipparcos parallaxes within 7.5%. Most importantly, the accuracy of our results does not degrade with increasing stellar distance. With the ongoing collection of high-resolution stellar spectra, our method is well-suited to complement Gaia.

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Probing the Galactic thick disc vertical properties and interfaces

Cited by 63 publications

References 68 publications

Chemodynamical evolution of the Milky Way disk

Chemodynamical evolution of the Milky Way disk

Chemical gradients in the Milky Way from the RAVE data

Climbing the cosmic ladder with stellar twins

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