THE DISTRIBUTION OF THE ELEMENTS IN THE GALACTIC DISK. III. A RECONSIDERATION OF CEPHEIDS FROM<i>l</i>= 30° TO 250°

Luck, R. E.; Lambert, David L.

doi:10.1088/0004-6256/142/4/136

Cited by 214 publications

(332 citation statements)

References 79 publications

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“…Both Cheng et al (2012) and Hayden et al (2014) have measured a steep radial gradients of about −0.06 dex kpc −1 (0.15 < | z| < 0.5 kpc) and −0.087±0.002 dex kpc −1 (0.0 < | z| < 0.25 kpc), respectively, close to the plane and have confirmed that the radial gradients become flatter as one moves away from the Galactic midplane in the vertical range 0.5 < | z| < 2 kpc. Again the sample of Cepheids used in measuring the radial abundance gradients is concentrated close to the Galactic plane within | z| < 0.5 kpc (Luck & Lambert 2011). At R gc > 12 kpc and away from the midplane, the mean metallicity of about −0.3 dex and the flat radial gradient observed for the present sample of OCs is consistent with very similar values reported for field dwarfs (Cheng et al 2012) and field giants (Hayden et al 2014).…”

Section: Radial Abundance Distribution Of Ocs and The Field Starssupporting

confidence: 90%

“…As a result, the initial and the present-day gradient derived for the younger populations are very similar out to 12 kpc. This fairly explains the similarity in the radial gradients observed for the younger tracers such as OCs of age less than 2 Gyr ( Figure 4 and figure 5), field stars (Cheng et al 2012;Hayden et al 2014) and Cepheids (Luck & Lambert 2011;Genovali et al 2014) for Rgc < 12 kpc. The steep gradient of slope −0.058 dex kpc −1 for stars younger than 2 Gyr in the radial range 6−11 kpc and a shallow gradient of old stellar populations predicted after taking the radial migration into account is in fair agreement with our values of gradient measured for respective age groups.…”

Section: Comparison With Chemodynamical Modelssupporting

confidence: 73%

“…Another fascinating result, in common for both the field stars and OCs at large radii, is the evidence for enhanced [α/Fe] ratios in the outer Galactic disc (Yong et al 2005;Bensby et al 2011;Luck & Lambert 2011). The fact that the α-enriched clusters older than 4−5 Gyr, reminiscent of rapid star formation history, have populated the Galactic disc beyond 12 kpc, where the star formation is slow due to low surface density of gas, is a puzzle in conflict with the inside-out formation scenarios of the Milky Way (Bovy et al 2012;Roškar et al 2013).…”

Section: Introductionmentioning

confidence: 98%

“…It is especially puzzling that the flattening of the metallicity distribution of OCs at large radii is not shown by the Galactic field stars (Cheng et al 2012;Hayden et al 2014) including Cepheids (Luck & Lambert 2011;Genovali et al 2014) where field stars suggest a constant steep decline of metallicity out to Rgc of 18 kpc. Another fascinating result, in common for both the field stars and OCs at large radii, is the evidence for enhanced [α/Fe] ratios in the outer Galactic disc (Yong et al 2005;Bensby et al 2011;Luck & Lambert 2011).…”

Section: Introductionmentioning

confidence: 99%

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The evolution of the Milky Way: new insights from open clusters

Reddy¹,

Lambert²,

Giridhar³

2016

Mon. Not. R. Astron. Soc.

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We have collected high-dispersion echelle spectra of red giant members in the twelve open clusters (OCs) and derived stellar parameters and chemical abundances for 26 species by either line equivalent widths or synthetic spectrum analyses. We confirm the lack of an age−metallicity relation for OCs but argue that such a lack of trend for OCs arise from the limited coverage in metallicity compared to that of field stars which span a wide range in metallicity and age. We confirm that the radial metallicity gradient of OCs is steeper (flatter) for R gc < 12 kpc (>12 kpc). We demonstrate that the sample of clusters constituting a steep radial metallicity gradient of slope −0.052±0.011 dex kpc −1 at R gc < 12 kpc are younger than 1.5 Gyr and located close to the Galactic midplane (| z| < 0.5 kpc) with kinematics typical of the thin disc. Whereas the clusters describing a shallow slope of −0.015±0.007 dex kpc −1 at R gc > 12 kpc are relatively old, thick disc members with a striking spread in age and height above the midplane (0.5 < | z| < 2.5 kpc). Our investigation reveals that the OCs and field stars yield consistent radial metallicity gradients if the comparison is limited to samples drawn from the similar vertical heights. We argue via the computation of Galactic orbits that all the outer disc clusters were actually born inward of 12 kpc but the orbital eccentricity has taken them to present locations very far from their birthplaces.

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Section: Radial Abundance Distribution Of Ocs and The Field Starssupporting

confidence: 90%

Section: Comparison With Chemodynamical Modelssupporting

confidence: 73%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The evolution of the Milky Way: new insights from open clusters

Reddy¹,

Lambert²,

Giridhar³

2016

Mon. Not. R. Astron. Soc.

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“…Several previous studies (Costa et al 2004;Jacobson et al 2011b;Yong et al 2012) have shown evidence for a transition to a flat radial gradient at large Galactocentric radii in the plane, with the transition occurring between 10 and 14 kpc. This flattening of the radial gradient is not observed with Cepheids Luck & Lambert 2011;Lemasle et al 2013). There is some question about whether the apparent flattening might arise if one does not consider vertical gradients when the radial gradients are measured (Cheng et al 2012b).…”

Section: Intermediate Radiimentioning

confidence: 89%

Chemical Cartography With Apogee: Large-Scale Mean Metallicity Maps of the Milky Way Disk

Hayden¹,

Holtzman²,

Bovy³

et al. 2014

171

195

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We present Galactic mean metallicity maps derived from the first year of the SDSS-III APOGEE experiment. Mean abundances in different zones of projected Galactocentric radius (0 < R < 15 kpc) at a range of heights above the plane (0 < |z| < 3 kpc), are derived from a sample of nearly 20,000 giant stars with unprecedented coverage, including stars in the Galactic mid-plane at large distances. We also split the sample into subsamples of stars with low-and high-[α/M] abundance ratios. We assess possible biases in deriving the mean abundances, and find that they are likely to be small except in the inner regions of the Galaxy. A negative radial metallicity gradient exists over much of the Galaxy; however, the gradient appears to flatten for R < 6 kpc, in particular near the Galactic mid-plane and for low-[α/M] stars. At R > 6 kpc, the gradient flattens as one moves off the plane, and is flatter at all heights for high-[α/M] stars than for low-[α/M] stars. Alternatively, these gradients can be described as vertical gradients that flatten at larger Galactocentric radius; these vertical gradients are similar for both low-and high-[α/M] populations. Stars with higher [α/M] appear to have a flatter radial gradient than stars with lower [α/M]. This could suggest that the metallicity gradient has grown steeper with time or, alternatively, that gradients are washed out over time by migration of stars.

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Gas Accretion via Condensation and Fountains

Fraternali

2017

Gas Accretion Onto Galaxies

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For most of their lives, galaxies are surrounded by large and massive coronae of hot gas, which constitute vast reservoirs for gas accretion. This Chapter describes a mechanism that allows star-forming disc galaxies to extract gas from their coronae. Stellar feedback powers a continuous circulation (galactic fountain) of gas from the disc into the halo, producing mixing between metal-rich disc material and metal-poor coronal gas. This mixing causes a dramatic reduction of the cooling time of the corona making it condense and accrete onto the disc. This fountain- driven accretion model makes clear predictions for the kinematics of the extraplanar cold/warm gas in disc galaxies, which are in good agreement with a number of independent observations. The amount of gas accretion predicted by the model is of the order of what is needed to sustain star formation. Accretion is expected to occur preferentially in the outer parts of discs and its efficiency drops for higher coronal temperatures. Thus galaxies are able to gather new gas as long as they do not become too massive nor fall into large halos and maintain their star-forming gaseous discs.Comment: 30 pages, 13 figures; invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

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THE DISTRIBUTION OF THE ELEMENTS IN THE GALACTIC DISK. III. A RECONSIDERATION OF CEPHEIDS FROMl= 30° TO 250°

Cited by 214 publications

References 79 publications

The evolution of the Milky Way: new insights from open clusters

The evolution of the Milky Way: new insights from open clusters

Chemical Cartography With Apogee: Large-Scale Mean Metallicity Maps of the Milky Way Disk

Gas Accretion via Condensation and Fountains

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