Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars From Sloan Digital Sky Survey Dr7

Carollo, D.; Beers, Timothy C.; Chiba, Masashi; Norris, John E.; Freeman, K. C.; Lee, Young Sun; Ivezić, Željko; Rockosi, Constance M.; Yanny, B.

doi:10.1088/0004-637x/712/1/692

Cited by 482 publications

(829 citation statements)

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“…In addition, a second peak around −2.1 is observed. This is very close to the median metallicity value associated with the outer-halo region (Carollo et al 2010;Allende Prieto et al 2014;FA15).…”

Section: [X/h] Vs Rsupporting

confidence: 78%

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Chemical trends in the Galactic halo from APOGEE data

Fernández-Alvar

Carigi

Prieto

et al. 2016

Mon. Not. R. Astron. Soc.

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The galaxy formation process in the Λ-Cold Dark Matter scenario can be constrained from the analysis of stars in the Milky Way's halo system. We examine the variation of chemical abundances in distant halo stars observed by the Apache Point Galactic Evolution Experiment (APOGEE), as a function of distance from the Galactic center (r) and iron abundance ([M/H]), in the range 5 r 30 kpc and −2.5 < [M/H] < 0.0. We perform a statistical analysis of the abundance ratios derived by the APOGEE pipeline (ASPCAP) and distances calculated by several approaches. Our analysis reveals signatures of a different chemical enrichment between the inner and outer regions of the halo, with a transition at about 15 kpc. The derived metallicity distribution function exhibits two peaks, at [M/H] ∼ −1.5 and ∼ −2.1, consistent with previously reported halo metallicity distributions. We obtain a difference of ∼ 0.1 dex for α-element-to-iron ratios for stars at r > 15 kpc and [M/H] > −1.1 (larger in the case of O, Mg and S) with respect to the nearest halo stars. This result confirms previous claims for low-α stars found at larger distances. Chemical differences in elements with other nucleosynthetic origins (Ni, K, Na, and Al) are also detected. C and N do not provide reliable information about the interstellar medium from which stars formed because our sample comprises RGB and AGB stars and can experience mixing of material to their surfaces.

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Section: [X/h] Vs Rsupporting

confidence: 78%

“…The derived MDF from [M/H] also shows a second peak at [M/H] ∼ −2.1, which resembles the median metallicity value associated with the outer-halo population (Carollo et al 2007(Carollo et al , 2010Beers et al 2012).…”

Section: Discussionmentioning

confidence: 65%

Chemical trends in the Galactic halo from APOGEE data

Fernández-Alvar

Carigi

Prieto

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The break in the stellar density profile could also be an indication that the Milky Way has a "dual stellar halo," containing populations of different origins (Carollo et al 2007(Carollo et al , 2010Beers et al 2012). Simulations predict that the stellar halo is composed both of accreted stars and stars that form in situ (e.g., Zolotov et al 2009;Font et al 2011;McCarthy et al 2012;Tissera et al 2012;Cooper et al 2015).…”

Section: Dual Stellar Halo: In Situ Star Formationmentioning

confidence: 99%

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

Cunningham

Deason

Guhathakurta

et al. 2016

ApJ

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We present the line-of-sight (LOS) velocities for 13 distant main sequence Milky Way halo stars with published proper motions (PMs). The PMs were measured using long baseline (5-7 years) multi-epoch Hubble Space Telescope/Advanced Camera for Surveys photometry, and the LOS velocities were extracted from deep (5-6 hr integrations) Keck II/DEIMOS spectra. We estimate the parameters of the velocity ellipsoid of the stellar halo using a Markov chain Monte Carlo ensembler sampler method. The velocity second moments in the directions of the Galactic (l, b, LOS) coordinate system are v 138 We use these ellipsoid parameters to constrain the velocity anisotropy of the stellar halo. Ours is the first measurement of the anisotropy parameter β using 3D kinematics outside of the solar neighborhood. We find 0.3 0.9 0.4 b = --+ , consistent with isotropy and lower than solar neighborhood β measurements by 2σ (β SN ∼0.5-0.7). We identify two stars in our sample that are likely members of the known TriAnd substructure, and excluding these objects from our sample increases our estimate of the anisotropy to 0.1 1.0which is still lower than solar neighborhood measurements by 1σ. The potential decrease in β with Galactocentric radius is inconsistent with theoretical predictions, though consistent with recent observational studies, and may indicate the presence of large, shell-type structure (or structures) at r∼25 kpc. The methods described in this paper will be applied to a much larger sample of stars with 3D kinematics observed through the ongoing HALO7D program.

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“…Hartwick (1987) showed that the metal-poor RR Lyrae stars delineate a two-component halo, with a flattened inner component and a spherical outer component. Carollo et al (2010) identified a two-component halo and the thick disk in a sample of 17,000 SDSS stars, mostly with [Fe/H] < −0.5. They described the kinematics well with these three components:…”

Section: The Galactic Stellar Halomentioning

confidence: 99%

Structure and Evolution of the Milky Way

Freeman

2011

Astrophysics and Space Science Proceedings

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This review discusses the structure and evolution of the Milky Way, in the context of opportunities provided by asteroseismology of red giants. The review is structured according to the main Galactic components: the thin disk, thick disk, stellar halo, and the Galactic bar/bulge. The review concludes with an overview of Galactic archaeology and chemical tagging, and a brief account of the upcoming HERMES survey with the AAT. The Thin Disk: Formation and EvolutionHere are some of the issues related to the formation and evolution of the Galactic thin disk:• Building the thin disk: its exponential radial structure, and the role of mergers.• The star formation history: chemical evolution and continued gas accretion.• Evolutionary processes in the disk: disk heating, radial mixing.• The outer disk: chemical properties and chemical gradients.Many of the basic observational constraints on the properties of the Galactic disk are still uncertain. At this time, we do not have reliable information about the star formation history of the disk. We do not know how the metallicity distribution and the stellar velocity dispersions in the disk have evolved with time. One might have expected that these observational questions were well understood by now, but this is not yet so. The basic observational problem is the difficulty of measuring ages for individual stars.The younger stars of the Galactic disk show a clear abundance gradient of about 0.07 dex kpc −1 , outlined nicely by the cepheids (Luck et al., 2006). In the outer disk, for the older stars, the abundance gradient appears to be even stronger: the

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Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars From Sloan Digital Sky Survey Dr7

Cited by 482 publications

References 124 publications

Chemical trends in the Galactic halo from APOGEE data

Chemical trends in the Galactic halo from APOGEE data

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

Structure and Evolution of the Milky Way

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