3D outer bulge structure from near infrared star counts

Abstract

We attempt to study the characteristics of the different stellar populations present in the Galactic central region. A Monte Carlo method is used to simultaneously fit 11 thin disc and triaxial outer bulge density parameters on (Ks,J-Ks) star count data in almost 100 windows from the DENIS near infrared large scale survey at -8 deg < l< 12 deg and -4 deg < b < 4 deg. Various bulge density profiles and luminosity functions were tested uing a population synthesis scheme. The best models, selected by a maximum likelihood test, give the following description: the outer bulge is proxy, prolate, and oriented 10.6+/-3 deg with respect to the Sun-center direction. It seems that the main bulge population is not older than 10 Gyr, but this preliminary result needs further work to be confirmed. A significant central hole is found in the middle of the thin disc. We discuss these results in regard to previous findings and the scenario of bulge formation.

17 pages, 12 figures, accepted for publication by A&A

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