Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars

Chris Wegg & Ortwin Gerhard, 2013, MNRAS, 435, 1874 (to the paper)
In the center we show an image of the 3D iso-density contours of the measured bulge density. Three projections are shown as surrounding plots: From above (i.e. from the North Galactic pole), from the side (i.e. along the intermediate axis of the bar) and the re-projected surface density from the sun. The three projections show the surface density of bulge red clump stars with isophotes spaced by 0.5 mag.

Using red clump giant stars identified in the VVV survey we produced the most accurate and high resolution map of the inner regions of the Milky Way. Our density map covers the inner (2.2x1.4x1.1)kpc of the bulge/bar. Line-of-sight density distributions were estimated by deconvolving extinction and completeness corrected K-band magnitude distributions. In constructing our measurement, we assumed that the three-dimensional bulge is 8-fold mirror triaxially symmetric, but the map is otherwise completely non-parametric. 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. Our 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.

Anyone is welcome to use the movie we made to vizualize the measured 3D structure. Just reference the original paper if you use the movie (Creative Commons attribution share-alike license).

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