Maximum Entropy Estimation of the Galactic Bulge Morphology via the VVV Red Clump

TL;DR

This paper uses maximum entropy deconvolution of Red Clump star data from the VVV survey to create a detailed 3D model of the Galactic bulge, improving understanding of its structure and relation to gamma-ray excess.

Contribution

It introduces a non-parametric, maximum entropy based method to reconstruct the Galactic bulge's 3D density from star counts, extending previous parametric models.

Findings

Estimated bulge mass between 13-17 billion solar masses.

Bulge X-component constitutes 18-25% of total mass.

Bulge angle with Sun-Galactic center line is 18-32 degrees.

Abstract

The abundance and narrow magnitude dispersion of Red Clump (RC) stars make them a popular candidate for mapping the morphology of the bulge region of the Milky Way. Using an estimate of the RC's intrinsic luminosity function, we extracted the three-dimensional density distribution of the RC from deep photometric catalogues of the VISTA Variables in the Via Lactea (VVV) survey. We used maximum entropy based deconvolution to extract the spatial distribution of the bulge from Ks-band star counts. We obtained our extrapolated non-parametric model of the bulge over the inner 40 by 40 degrees squared region of the Galactic centre. Our reconstruction also naturally matches onto a parametric fit to the bulge outside the VVV region and inpaints overcrowded and high extinction regions. We found a range of bulge properties consistent with other recent investigations based on the VVV data. In particular, we estimated the bulge mass to be in the range 13 to 17 billion solar masses, the X-component to be between 18% and 25% of the bulge mass, and the bulge angle with respect to the Sun-Galactic centre line to be between 18 and 32 degrees. Studies of the Fermi Large Area Telescope (LAT) gamma-ray Galactic centre excess suggests that the excess may be traced by Galactic bulge distributed sources. We applied our deconvolved density in a template fitting analysis of this Fermi-LAT GeV excess and found an improvement in the fit compared to previous parametric based templates.