The Bones of the Milky Way

The Milky Way is typically thought of as a spiral galaxy, but our understanding of its detailed structure remains vague thanks to our observational vantage point within its disk. Most of what we do know about the Milky Way's three-dimensional geometry comes from velocity-resolved observations of gas and stars. But, recently, it has become possible to combine exquisitely sensitive observations of dust with more traditional kinematically-resolved observations of gas to reveal totally new structures within the Milky Way. In this talk, I will explain why we now believe that some extraordinarily long so-called "infrared dark clouds" are in fact the "bones" of the Galaxy, marking out the true mid-plane of its disk to within less than a few parsecs. We call the long features "bones" thanks to recent numerical simulations of spiral galaxies that show a network of over-dense filaments within and between the arms that resemble an endoskeleton for a galaxy. The talk will highlight how both large surveys and new visualization tools have been critical in this investigation. By way of example, I will argue that the "Nessie" Infrared Dark Cloud is a nearly-continuous, many-hundreds-of-pc-long, ~pc-thick, structure, lying within a few pc of the mid-plane of the MIlky Way.