Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry

By M. Zoccali, A. Renzini, Sergio Ortolani, L. Greggio, I. Saviane, Santi Cassisi, M. Rejkuba, B. Barbuy, R. Rich, E. Bica. 2002

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We present a new determination of the metallicity distribution, age, and luminosity function of the Galactic bulge stellar population. By combining near-IR data from the 2MASS survey, from the SOFI imager at ESO NTT and the NICMOS camera on board HST we were able to construct color-magnitude diagrams (CMD) and luminosity functions (LF) with large statistics and small photometric errors from the Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) tip down to ∼0.15 M� . This is the most extended and complete LF so far obtained for the galactic bulge. Similar near-IR data for a disk control field were used to decontaminate the bulge CMDs from foreground disk stars, and hence to set a stronger constraint on the bulge age, which we found to be as large as that of Galactic globular clusters, or >10 Gyr. No trace is found for any younger stellar population. Synthetic CMDs have been constructed to simulate the effect of photometric errors, blending, differential reddening, metallicity dispersion and depth effect in the comparison with the observational data. By combining the near-IR data with optical ones, from the Wide Field Imager at the ESO/MPG 2.2 m telescope, a disk-decontaminated (MK,V-K )C MD has been constructed and used to derive the bulge metallicity distribution, by comparison with empirical RGB templates. The bulge metallicity is found to peak at near solar value, with a sharp cutoff just above solar, and a tail towards lower metallicity that does not appreciably extend below (M/H) ∼− 1.5.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6fa24692c6587ce08aa1cd103d53117b87d1960c

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. T. Naab
4. O. Gerhard
5. A. Dekel
6. R. Dav'e
7. R. Genzel
8. Volker Springel

In Atomic and Molecular Physics, and Optics

1. T. Alexander
2. R. Genzel
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In Instrumentation

1. P. Hopkins
2. L. Hernquist
3. A. Renzini
4. T. Naab
5. A. Dekel
6. O. Gerhard
7. R. Genzel
8. R. Dav'e

Citations in the corpus

• Effects of supernova feedback on the formation of galaxy discs (2008, background): “The stellar halo is found to be the most metal-poor component, the thin disk and the bulge are the most metal-rich components (e.g. Ryan & Nories 1991; Chiba & Beers 2000; Zoccali et al. 2003; Nordström et al. 2004).”
• The evolution of isotope ratios in the Milky Way Galaxy (2011, background): “The observed MDF in the Galactic bulge was updated by Zoccali et al. (2008), where the peak metallicity is significantly higher than the previous MDF by Zoccali et al. (2003).”
• Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “The double clump is clearly visible in several color magnitude diagrams available in the literature (e.g. Zoccali et al. 2003; Rattenbury et al. 2007; McWilliam & Zoccali 2010; Nataf et al. 2010).”
• Abundances of Baade’s Window Giants from Keck HIRES Spectra. II. The Alpha and Light Odd Elements (2006, result): “Recent studies that confirm the old, metal rich nature of the bulge population (Kuijken & Rich 2002; Zoccali et al. 2003), and most recently, the revised bulge abundance scale (Paper I).”
• StarHorse : a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars (2017, positive): “If stellar ages are available as well, they can be used to probe the chemo-dynamical evolution of different Galactic components much more directly (e.g., Zoccali et al. 2003; Haywood et al. 2013; Mitschang et al. 2014; Anders et al. 2017; Mackereth et al. 2017).”
• The metallicity distribution of bulge clump giants in Baade’s window (2011, methodology): “This disagreement was expected given the differences between our bulge MD and the one of Zoccali et al. (2003) and Fulbright et al. (2006), which were used as references by Ballero et al. (2007b).”
• The 511 keV emission from positron annihilation in the Galaxy (2010, background): “By comparing colour-magnitude diagrams of stars in the bulge and in metal-rich globular clusters, Zoccali et al. (2003) find that the populations of the two systems are co-eval, with an age of ∼10 Gyr.”
• TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE (2010, methodology): “Thus, for double RCs due to age and metallicity, rather than distance, there should be large numbers of both young and old populations in the Zoccali et al. (2003) field; yet no significant 6 Gyr population is evident in the Zoccali et al. (2003) data.”
• The Adequacy of Stellar Evolution Models for the Interpretation of the Color-Magnitude Diagrams of Resolved Stellar Populations (2005, background): “…distribution of stars on the RGB for retrieving their metallicity distribution (e.g., Mould, Kristian & Da Costa 1983; Armandroff et al. 1993; Grillmair et al. 1996; Harris & Harris 2002; Bellazzini et al. 2003; Zoccali et al. 2003; Tiede, Sarajedini & Barker 2004; Durrell, Harris & Pritchet 2004).”
• An Extended Star Formation History for the Galactic Center from Hubble Space Telescope NICMOS Observations (2003, background): “Further, how can a galaxy with a bulge population well demonstrated to be as old as the oldest globular clusters (Ortolani et al. 1995; Kuijken & Rich 2002; Zoccali et al. 2003), have formed at early times without simultaneously forming the bulk of the stars presently seen in the nuclear population?”
• Gas physics, disk fragmentation, and bulge formation in young galaxies (2003, background): “On the other hand, results from Ramirez et al. (2000) and Zoccali et al. (2003) point to a more metal rich distribution.”
• Stellar Population Diagnostics of Elliptical Galaxy Formation (2006, background): “Looking near to us, HST and ground based photometry of individual stars in the Galactic bulge have shown that they are older than at least 10 Gyr, with no detectable trace of an intermediate age component (Ortolani et al. 1995, Kuijken & Rich 2002, Zoccali et al. 2003).”
• The Multiplicity of the Subgiant Branch of ω Centauri: Evidence for Prolonged Star Formation (2007, background): “13 in Zoccali et al. 2003) and are ignored here.”
• The Stellar Cusp around the Supermassive Black Hole in the Galactic Center (2003, methodology): “In the range 14 Ks 19, the overall KLF is similar to but somewhat flatter than the KLF of the bulge of the Milky Way several degrees from the center ( 0:3; Alexander & Sternberg 1999; Tiede, Frogel, & Terndrup 1995; Zoccali et al. 2003) and the KLF on 30 pc scales around the center (Figer 2003).”
• OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION (2010, background): “But those stars could have formed over a short period of time but long before the bar structure formed (Wyse 1999; Freeman 2008), their old age (Zoccali et al. 2003; Fulbright et al. 2007) is therefore not an argument against the internal secular evolu- tion model.”
• Stellar Proper Motions in the Galactic Bulge from Deep Hubble Space Telescope ACS WFC Photometry (2008, background): “…reinforced by a later study employing statistical subtraction to take off a scaled contamination from a comparison field in the foreground disk; globular cluster comparison suggested an old, metal-rich population to fit the bulge well, but without a precise age distribution (Zoccali et al. 2003).”