2013MNRAS.435.1874W

The inner Milky Way is dominated by a boxy, triaxial bulge which is believed to have formed through disc instability processes. Despite its proximity, its large-scale properties are still not very well known, due to our position in the obscuring Galactic disc. Here, we make a measurement of the three-dimensional density distribution of the Galactic bulge using red clump giants identified in DR1 of the Vista Variables in the Via Lactea survey. Our density map covers the inner (2.2x1.4x1.1)kpc of the bulge/bar. Line-of-sight density distributions are estimated by deconvolving extinction- and completeness-corrected Ks-band magnitude distributions. In constructing our measurement, we assume that the three-dimensional bulge is eightfold mirror triaxially symmetric. In doing so, we measure the angle of the bar-bulge to the line of sight to be (27±2)°, where the dominant error is systematic arising from the details of the deconvolution process. The resulting density distribution shows a highly elongated bar with projected axis ratios ~(1:2.1) for isophotes reaching ∼ 2kpc along the major axis. Along the bar axes the density falls off roughly exponentially, with axis ratios (10:6.3:2.6) and exponential scalelengths (0.70:0.44:0.18)kpc. From about 400 pc above the Galactic plane, the bulge density distribution displays a prominent X-structure. Overall, the density distribution of the Galactic bulge is characteristic for a strongly boxy/peanut-shaped bulge within a barred galaxy.