A new photometric model of the Galactic bar using red clump giants

We present a study of the luminosity density distribution of the Galactic bar using number counts of red clump giants from the Optical Gravitational Lensing Experiment (OGLE) III survey. The data were recently published by Nataf et al. for 9019 fields towards the bulge and have 2.94 x 10(6) RC stars over a viewing area of 90.25 deg(2). The data include the number counts, mean distance modulus (mu), dispersion in mu and full error matrix, from which we fit the data with several triaxial parametric models. We use the Markov Chain Monte Carlo method to explore the parameter space and find that the best-fitting model is the E-3 model, with the distance to the GC 8.13 kpc, the ratio of semimajor and semiminor bar axis scalelengths in the Galactic plane x(0), y(0) and vertical bar scalelength z(0) x(0): y(0): z(0) approximate to 1.00: 0.43: 0.40 (close to being prolate). The scalelength of the stellar density profile along the bar's major axis is similar to 0.67 kpc and has an angle of 29 degrees.4, slightly larger than the value obtained from a similar study based on OGLE-II data. The number of estimated RC stars within the field of view is 2.78 x 10(6), which is systematically lower than the observed value. We subtract the smooth parametric model from the observed counts and find that the residuals are consistent with the presence of an X-shaped structure in the Galactic Centre, the excess to the estimated mass content is similar to 5.8 per cent. We estimate that the total mass of the bar is similar to 1.8 x 10(10) M-circle dot. Our results can be used as a key ingredient to construct new density models of the Milky Way and will have implications on the predictions of the optical depth to gravitational microlensing and the patterns of hydrodynamical gas flow in the Milky Way.