The metallicity distribution of bulge clump giants in Baade’s window

By V. Hill, A. Lecureur, A. Gómez, M. Zoccali, M. Schultheis, C. Babusiaux, F. Royer, B. Barbuy, Frédéric Arenou, D. Minniti and 1 more. 2011

174 citations recorded by the source corpus.

Aims. We seek to constrain the formation of the Galactic bulge by analysing the detailed chemical composition of a large sample of red clump stars in Baade’s window. These stars were selected to minimise the contamination by other Galactic components, so they are good tracers of the bulge metallicity distribution in Baade’s window, at least for stars more metal-rich than ∼−1.5. Methods. We used an automatic procedure to measure [Fe/H] differentially with respect to the metal-rich star μLeo in a sample of 219 bulge red clump stars from R = 20 000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT. For a subsample of 162 stars, we also derived [Mg/H] from spectral synthesis around the Mg i triplet at λ 6319 A. Results. The Fe and Mg metallicity distributions are both asymmetric with median values of +0.16 and +0.21, respectively. They show only a small proportion of stars at low metallicities, extending down to [Fe/H] = −1. 1o r [Mg/H] = −0.7. The iron distribution is clearly bimodal, as revealed both by a deconvolution (from observational errors) and a Gaussian decomposition. The decomposition of the observed Fe and Mg metallicity distributions into Gaussian components yields two populations of equal sizes (50% each): a metal-poor component centred on [Fe/H] = −0.30 and [Mg/H] = −0.06 with a large dispersion and a narrow metal-rich component centred on [Fe/H] =+ 0.32 and [Mg/H] =+ 0.35. The metal-poor component shows high [Mg/Fe] ratios (around 0.3), while stars in the metal-rich component are found to have nearly solar ratios. Kinematical differences between the two components have also been found: the metal-poor component shows kinematics compatible with an old spheroid, while the metal-rich component is consistent with a population supporting a bar. In view of their chemical and kinematical properties, we suggest different formation scenarii for the two populations: a rapid formation time scale as an old spheroid for the metal-poor component (old bulge) and for the metal-rich component, a formation on a longer time scale driven by the evolution of the bar (pseudo-bulge). The observations are described well by a simple model consisting of two components: a simple closed box model to predict the metal-poor population contribution and a local thin disc metallicity distribution, shifted in metallicity, to represent the metal-rich population. The pseudo-bulge is compatible with its being formed from the inner thin disc, assuming high (but plausible) values of the gradients in the early Galactic disc.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/621fd4f7fde125a0f90b7abeca38fc52ad58b50e

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way (2012, methodology): “This is similar to the components identified by Hill et al. (2011) and by Babusiaux et al. (2010) in theirb = −4◦ field.”
REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S RV ∼ 2.5 EXTINCTION CURVE (2012, methodology): “It could be due to a difference in the mean metallicity of sightlines studied by Bensby et al. (2011) and that studied by Hill et al. (2011).”
Nucleosynthesis in Stars and the Chemical Enrichment of Galaxies (2013, background): “Recent observational data suggest two populations in the Galactic bulge: a metal-rich bar and a metalpoor classical bulge (Babusiaux et al. 2010, Hill et al. 2011, Uttenthaler et al. 2012; but see Ness & Freeman 2012).”
Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data (2011, methodology): “…and radial velocity distribution from the RGB, Gonzalez et al. (2011) completed the data with the abundances of alpha abundances, Babusiaux et al (2010) studied the correlation between metallicity and kinematics and Hill et al (2011) computed the MDF from the red clump giants for Baade’s window.”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “…et al. 2010; Ness et al. 2013a,b; Rojas-Arriagada et al. 2014) or perhaps even a classical c© 2015 RAS spheroidal bulge (e.g., Babusiaux et al. 2010; Hill et al. 2011), although the existence of the latter has been called into question by model fits to stellar counts in the 2MASS and SDSS catalogs…”
Gaia FGK benchmark stars: Effective temperatures and surface gravities (2015, background): “Hill et al. (2011) studied the formation of the Galactic bulge by determining metallicities for clump giants in Baade’s window relative to the metal-rich giant µ Leo.”
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Galactic bulge studies (2012, background): “…to the population associated with the bar, there are hints of a second chemically and kinematically distinct component (Babusiaux et al. 2010; Hill et al. 2011; Gonzalez et al. 2011b; Bensby et al. 2011); and iv) the GB is dominated by old stars (Zoccali et al. 2003; Brown et al. 2010;…”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “…disk, the thick disk and bulge are more difficult to disentangle because they share kinematic and abundance characteristics, as observed in red giants (Alves-Brito et al. 2010, Ryde et al. 2010, Gonzalez et al. 2011b, Hill et al. 2011) and microlensed dwarf stars (Bensby et al. 2009, 2013).”
LSST: From Science Drivers to Reference Design and Anticipated Data Products (2008, background): “31 • Detailed constraints on the formation and evolution of the populations within the Galactic Bulge, as traced by the spatial distribution, motion, and chemistry of ∼107−8 of its stars (e.g., Hill et al. 2011; Ness et al. 2014).”