Extinction law and stellar mass in the Nuclear Bulge from kinematically-selected red clump stars

TL;DR

This study measures the extinction law and stellar mass in the Milky Way's Nuclear Bulge using kinematically-selected red clump stars, providing high-resolution reddening maps and consistent mass estimates.

Contribution

Developed a method to determine the extinction law and stellar mass in the Nuclear Bulge using kinematic selection and red clump star counts.

Findings

Extinction ratios consistent with previous studies.

High-resolution reddening map reveals filamentary structures.

Estimated stellar mass of the Nuclear Bulge is approximately 1.2×10^9 solar masses.

Abstract

The Nuclear Bulge of the Milky Way harbors stellar populations that provide crucial insights into galaxy formation processes and serve as a nearby analog for understanding bulge formation in external galaxies. However, detailed studies of this region are severely hampered by extreme and highly variable interstellar extinction, which obscures the intrinsic stellar properties and impedes accurate stellar mass determinations. Our goal is to measure the extinction law towards the Nuclear Bulge and to estimate its stellar density. We developed a method to determine the extinction law towards the Nuclear Bulge by kinematically selecting red clump stars belonging to this region. We created a high-spatial resolution reddening map, and computed stellar mass with completeness-corrected red clump star counts, scaled from empirical measurements. We find a total-to-selective extinction ratio of $\mathrm{A_K/{E_{H-K}} = 1.259 \pm 0.074}$, and an extinction ratio of $\mathrm{A_H/A_K = 1.794 \pm 0.046}$, which are consistent with previous works. The high-spatial resolution reddening map shows clear filamentary structures, and a gradient in the extinction over the giant molecular cloud G0.253+0.016 (i.e., the Brick). From the star counts, we measured a stellar mass of $\mathrm{12.2~\pm2.6\times10^8~M_{\odot}}$ for the Nuclear Bulge, in agreement with other mass estimates.