Milky Way demographics with the VVV Survey III. Evidence for a Great Dark Lane in the 157 Million Star Bulge Color-Magnitude Diagram

TL;DR

This paper uses near-infrared data from the VVV Survey to identify a large, optically thick dust lane in the Milky Way bulge, called the 'Great Dark Lane', which influences galactic models and stellar observations.

Contribution

It provides the first evidence for a significant dark dust lane in the Galactic bulge using color-magnitude diagram analysis of 157 million stars.

Findings

Identification of the Great Dark Lane in the bulge

The lane causes a 0.55 magnitude color split in the red giant clump

The lane is located in front of the bulge, spanning several degrees in longitude

Abstract

The new generation of IR surveys are revealing and quantifying Galactic features, providing an improved 3-D interpretation of our own Galaxy. We present an analysis of the global distribution of dust clouds in the bulge using the near-IR photometry of 157 million stars from the VVV Survey. We investigate the color magnitude diagram of the Milky Way bulge which shows a red giant clump of core He burning stars that is split in two color components, with a mean color difference of (Z-Ks)=0.55 magnitudes equivalent to A_V=2.0 magnitudes. We conclude that there is an optically thick dust lane at intermediate latitudes above and below the plane, that runs across several square degrees from l=-10 deg to l=+10 deg. We call this feature the "Great Dark Lane". Although its exact distance is uncertain, it is located in front of the bulge. The evidence for a large-scale great dark lane within the Galactic bulge is important in order to constrain models of the barred Milky Way bulge and to compare our galaxy with external barred galaxies, where these kinds of features are prominent. We discuss two other potential implications of the presence of the Great Dark Lane for microlensing and bulge stellar populations studies.