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

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

Corresponding author: M. Zoccali, mzoccali@eso.org

Received: 25 June 2002
Accepted: 22 October 2002

Abstract

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 ~. 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 (M_K,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] .