Toward a More Complete Picture of Dust Extinction

The extinction curve in a given line of sight represents the amount of light lost due to dust as a function of wavelength. In the Milky Way, a single average curve is used in a wide range of applications. In reality, the shape of this curve varies among sightlines; it is non-universal. This non-universality has impacts in several areas. Usually, dust is represented in the gas-to-dust ratio by E(B-V), the reddening. However, there is no reason that E(B-V) is most closely associated with gas density. In fact, using full extinction curves within the Milky Way, we find that extinction in the UV (specifically, at 2900 Å) better correlates with hydrogen column density, and is thus a better physical measure of dust than E(B-V). In the near-infrared, extinction has been found to follow a simple power-law form (e.g., Rieke & Lebofsky 1985). Fixed values for the exponent of the power law are usually taken. In a second study, we analyze a large sample of MW sightlines with data from SDSS and 2MASS to examine the potential variance of the power-law form of the near-IR extinction curve with dust column density. We also investigate power-law variance in the optical, and extend into the UV using similar methods. In all three of these wavelength regions, we particularly focus on the less-well-studied regime of low dust column densities.