Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red
  Clump Stars
  The inner Milky Way is dominated by a boxy, triaxial bulge which is believed
to have formed through disk instability processes. Despite its proximity, its
large-scale properties are still not very well known, due to our position in
the obscuring Galactic disk. Here we make a measurement of the
three-dimensional density distribution of the Galactic bulge using red clump
giants identified in DR1 of the VVV 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 K-band
magnitude distributions. In constructing our measurement, we assume that the
three-dimensional bulge is 8-fold mirror triaxially symmetric. In doing so we
measure the angle of the bar-bulge to the line-of-sight to be (27+- 2)deg,
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 scale-lengths
(0.70:0.44:0.18)kpc. From about 400pc 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.
