Mapping the three-dimensional density of the Galactic bulge with VVV red clump stars

• Published in: Monthly notices of the Royal Astronomical Society 2013-11, Vol.435 (3), p.1874-1887
• Main Authors: Wegg, Christopher, Gerhard, Ortwin
• Format: Article
• Language: English
• Subjects: Density; Milky Way; Protoplanetary disks
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt1376

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 (2.2 × 1.4 × 1.1) kpc of the bulge/bar. Line-of-sight density distributions are estimated by deconvolving extinction- and completeness-corrected K s-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 ∼2 kpc 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.