2012ApJ...753L..24L

We investigate the extinction, together with the radial velocity (RV) dispersion and distribution of red clump stars in the anticenter direction using spectra obtained with Hectospec on the MMT. We find that extinction peaks at Galactocentric radii of about 9.5 and 12.5 kpc, right in front of the locations of the Perseus and Outer arms and in line with the relative position of dust and stars in external spiral galaxies. The RV dispersion peaks around 10 kpc, which coincides with the location of the Perseus arm, yields an estimated arm-interarm density contrast of 1.3-1.5, and is in agreement with previous studies. Finally, we discover that the RV distribution bifurcates around 10-11 kpc into two peaks at +27 km/s and -4 km/s. This seems to be naturally explained by the presence of the outer Lindblad resonance of the Galactic bar, but further observations will be needed to understand if the corotation resonance of the spirals arms also plays a role.