A Tale of Two Dust Disks in Our Milky Way

TL;DR

This study reveals the existence of two distinct dust disks in the Milky Way, detailing their structure, scale lengths, and correlation with hydrogen gas, based on extensive stellar measurements.

Contribution

First detection and characterization of separate thin and thick dust disks in the Milky Way using multi-faceted stellar data.

Findings

Identified two dust disk components at 5-14 kpc Galactocentric distance.

Measured scale heights and lengths for both dust disks.

Found a radial gradient in the gas-to-dust ratio.

Abstract

Cosmic dust plays a vital role in stellar and galactic formation and evolution, but its three-dimensional structure in the Milky Way has remained unclear due to insufficient precise reddening and distance measurements. Although early studies typically adopted a single-disk model, we detect two distinct components at Galactocentric distances of 5-14 kpc, enabled by photometric, spectroscopic, and astrometric measurements of over 5 million stars. The thin dust disk's scale height increases radially from 60 to 200 pc, while the thick disk grows from 300 to 800 pc. For the first time, we find the thin and thick dust disk correlates spatially with molecular and atomic hydrogen disk, respectively. The thin, thick, and combined disks have scale lengths of 9.6+1.2-1.1 kpc, 4.2+0.4-0.3 kpc, and 6.6+0.3-0.3 kpc, respectively. The gas-to-dust ratio shows an exponential radial gradient, increasing from around 60 at 5 kpc to around 470 at 14 kpc. These findings provide new insights into dust morphology in the Galaxy and raise fundamental questions that require further investigation.