EDP Sciences
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Volume 399, Number 3, March I 2003
Page(s) 931 - 956
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021604

A&A 399, 931-956 (2003)
DOI: 10.1051/0004-6361:20021604

Age and metallicity distribution of the Galactic bulge from extensive optical and near-IR stellar photometry

M. Zoccali1, A. Renzini1, S. Ortolani2, L. Greggio3, I. Saviane4, S. Cassisi5, M. Rejkuba1, B. Barbuy6, R. M. Rich7 and E. Bica8

1  European Southern Observatory, Karl Schwarzschild Strasse 2, 85748, Garching bei München, Germany
    e-mail: arenzini@eso.org; mrejkuba@eso.org
2  Università di Padova, Dipart. di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: ortolani@pd.astro.it
3  INAF, Osservatorio Astronomico di Padova, Padova, Italy
    e-mail: greggio@pd.astro.it
4  European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
    e-mail: isaviane@eso.org
5  INAF, Osservatorio Astronomico Collurania, 64100, Teramo, Italy
    e-mail: cassisi@te.astro.it
6  Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil
    e-mail: barbuy@astro.iag.usp.br
7  Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562
    e-mail: rmr@astro.ucla.edu
8  Universidade Federal do Rio Grande do Sul, Dept. de Astronomia, CP 15051, Porto Alegre 91501-970, Brazil
    e-mail: bica@if.ufrgs.br

(Received 25 June 2002 / Accepted 22 October 2002 )

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 ~ $0.15~M_\odot$. 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 $\ga$ 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) CMD 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]  $\sim-1.5$.

Key words: Galaxy: bulge -- stars: Hertzsprung-Russell (H-R) and C-M diagrams -- stars: luminosity function, mass function

Offprint request: M. Zoccali, mzoccali@eso.org

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