Title: A new technique for mapping non-axisymmetric structure in the Milky Way's stellar disk
Author: Robert Benjamin
Institution: University of Wisconsin-Whitewater/Madison 

Abstract:  Using data from the Spitzer Space Telescope GLIMPSE/Legacy project and the UKIDSS 
Galactic plane survey, I present a new diagnostic diagram for identifying large scale stellar structures in the 
Milky Way Galaxy, analogous to the well-used longitude-velocity diagram used for HI/CO surveys. For a 
given latitude slice, one plots the slopes of point source histogram as a function of longitude and magnitude. 
Because most of the sources brighter than mag=12 are giants, common classes of giants, such as red 
clump giants,  asymptotic giant branch bump, and the tip of red giant branch produce detectable changes of 
slope in the source histograms. (This is only true because of the greatly reduced extinction in near and 
mid-infrared wavelengths.)  The apparent magnitude of the inflections in these histograms changes with 
longitude, allowing one to map regions of stellar over-density in the Galaxy. The Long Bar was first mapped 
this way by Benjamin et al (2005, see Figure 4). We show an update of this work, with constraints on the 
3-D structure of the triaxial bulge and Long Bar. We also show that a lower amplitude stellar overdensity in 
the inner Galaxy is plausibly identified at the Scutum-Crux (or Scutum-Centaurus) arm, at a distance that 
agrees better with the extinction distance of Marshall et al (2010) than kinematic distances. The amplitude 
of the stellar arm is constrained using both TRILEGAL (Girardi et al 2005) and Besancon (Robin et al 2003) 
models.  I present some additional (surprising) results on Galactic structure using this technique, discuss 
some of the principal limitations, and outline future directions.