Stellar populations in the Galactic bulge. Modelling the Galactic bulge with TRILEGAL

Aims: The aim of this paper is to study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge. We study the entire stellar population, but also retrieve information using only the red clump stars.
Methods: To study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge, we compared the output of the galaxy model TRILEGAL, which implements the Binney et al. (1997, MNRAS, 288, 365) bulge model, with observations from 2MASS and OGLE-II. A minimisation procedure has been set up to retrieve the best fitting model with different stellar populations and metallicity distributions.
Results: Using the TRILEGAL code we find that the best model resembling the characteristics of the Galactic bulge is a model with the distance to the Galactic centre R₀ = 8.7± ^0.57_0.43 kpc, the major axis ratios of the bar 1{:}η {:}zeta = 1{:}0.68±_0.19^0.05{:} 0.31±_0.04^0.06, and the angle between the Sun-centre line and the bar φ = 15^circ ± _12.7^13.3. Using these parameters the best model is found for a burst of 8 Gyr, although it is almost indistinguishable from models with ages of 9 and 10 Gyr. The metallicity distribution found is consistent with metallicity distributions in the literature based on spectroscopic results.