ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way
Melissa Ness,Kenneth C. Freeman,E. Athanassoula,E. Wylie-de-Boer,Joss Bland-Hawthorn,Martin Asplund,Geraint F. Lewis,David Yong,Rebecca Lane,László L. Kiss,László L. Kiss,László L. Kiss +11 more
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In this article, the authors present the metallicity results from the ARGOS spectroscopic survey of the Galactic bulge and propose that the stars with [Fe/H] ≥ 0.5 are part of the boxy/peanut bar/bulge.Abstract:
We present the metallicity results from the ARGOS spectroscopic survey of the Galactic bulge. Our aim is to understand the formation of the Galactic bulge: did it form via mergers, as expected from Lambda cold dark matter theory, or from disc instabilities, as suggested by its boxy/peanut shape, or both? Our stars are mostly red clump giants, which have a well-defined absolute magnitude from which distances can be determined. We have obtained spectra for 28 000 stars at a spectral resolution of R = 11 000. From these spectra, we have determined stellar parameters and distances to an accuracy of \textless1.5 kpc. The stars in the inner Galaxy span a large range in [Fe/H], -2.8 \textless= [Fe/H] \textless= +0.6. From the spatial distribution of the red clump stars as a function of [Fe/H], we propose that the stars with [Fe/H] \textgreater -0.5 are part of the boxy/peanut bar/bulge. We associate the lower metallicity stars ([Fe/H] \textless -0.5) with the thick disc, which may be puffed up in the inner region, and with the inner regions of the metal-weak thick disc and inner halo. For the bulge stars with [Fe/H] \textgreater -0.5, we find two discrete populations: (i) stars with [Fe/H] approximate to -0.25 which provide a roughly constant fraction of the stars in the latitude interval b = -5 degrees to -10 degrees, and (ii) a kinematically colder, more metal-rich population with mean [Fe/H] approximate to +0.15 which is more prominent closer to the plane. The changing ratio of these components with latitude appears as a vertical abundance gradient of the bulge. We attribute both of these bulge components to instability-driven bar/bulge formation from the thin disc. We associate the thicker component with the stars of the early less metal-rich thin disc, and associate the more metal-rich population concentrated to the plane with the colder more metal-rich stars of the early thin disc, similar to the colder and younger more metal-rich stars seen in the thin disc in the solar neighbourhood today. We do not exclude a weak underlying classical merger-generated bulge component, but see no obvious kinematic association of any of our bulge stars with such a classical bulge component. The clear spatial and kinematic separation of the two bulge populations (i) and (ii) makes it unlikely that any significant merger event could have affected the inner regions of the Galaxy since the time when the bulge-forming instabilities occurred.read more
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The Galaxy in Context: Structural, Kinematic, and Integrated Properties
TL;DR: In this paper, the authors review the key integrated, structural and kinematic parameters of the Galaxy, and point to uncertainties as well as directions for future progress, and show that the Galaxy is a luminous (L⋆) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo.
Journal ArticleDOI
CHEMICAL CARTOGRAPHY with APOGEE: METALLICITY DISTRIBUTION FUNCTIONS and the CHEMICAL STRUCTURE of the MILKY WAY DISK
Michael R. Hayden,Jo Bovy,Jon A. Holtzman,David L. Nidever,Jonathan C. Bird,David H. Weinberg,Brett H. Andrews,Steven R. Majewski,Carlos Allende Prieto,Carlos Allende Prieto,Friedrich Anders,Timothy C. Beers,Dmitry Bizyaev,Cristina Chiappini,Katia Cunha,Peter M. Frinchaboy,D. A. García-Hernández,D. A. García-Hernández,Ana E. García Pérez,Ana E. García Pérez,Ana E. García Pérez,Léo Girardi,Paul Harding,Fred Hearty,Fred Hearty,Jennifer A. Johnson,Szabolcs Mészáros,Ivan Minchev,Robert W. O'Connell,Kaike Pan,Annie C. Robin,Ricardo P. Schiavon,Donald P. Schneider,Mathias Schultheis,Matthew Shetrone,Michael F. Skrutskie,Matthias Steinmetz,Verne V. Smith,John C. Wilson,Olga Zamora,Olga Zamora,Gail Zasowski +41 more
TL;DR: In this paper, the authors measured the distribution of stars in the [/Fe] versus [Fe/H] plane and the metallicity distribution functions (MDFs) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height kpc.
Journal ArticleDOI
Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
Michael R. Hayden,Jo Bovy,Jon A. Holtzman,David L. Nidever,Jonathan C. Bird,David H. Weinberg,Brett H. Andrews,Carlos Allende Prieto,Friedrich Anders,Timothy C. Beers,Dmitry Bizyaev,Cristina Chiappini,Katia Cunha,Peter M. Frinchaboy,D. A. García-Hernández,Ana G. Pérez,Léo Girardi,Paul Harding,Fred R. Hearty,Jennifer A. Johnson,Steven R. Majewski,Szabolcs Mészáros,Ivan Minchev,Robert W. O'Connell,Kaike Pan,Annie C. Robin,Ricardo P. Schiavon,Donald P. Schneider,Mathias Schultheis,Matthew Shetrone,Michael F. Skrutskie,Matthias Steinmetz,Verne V. Smith,Olga Zamora,Gail Zasowski +34 more
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Journal ArticleDOI
Near-Field Cosmology with Extremely Metal-Poor Stars
Anna Frebel,John E. Norris +1 more
TL;DR: The most metal-poor stars in the Galactic halo and satellite dwarf galaxies provide an opportunity to explore the chemical and physical conditions of the earliest star-forming environments in the Universe.
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