The combination of extinction and scattering (i.e., attenuation) due to dust grains remain a critical uncertainty; for nearly all astronomical measurements, one needs to account for the dust in space. A technique to obtain extra-galactic spatially resolved attenuation measurements is to use partially overlapping -occulting- galaxy pairs: an astrophysical experiment in the optical properties of the interstellar medium that models the light of both galaxies and infers the missing light in the regions of overlap. In this talk, I present attenuation, reddening slope (RV) and color excess ratio (Eλ-V/EB-V) measurements mapped pixel-by-pixel from optical to near infrared wavelengths within the overlap of geometrically ideal occulting galaxy pair VV191. I will discuss what we learn about the dust properties of this galaxy pair and show that attenuation inferred from the Balmer decrement is twice that of the total average attenuation through the disk, decreasing with galactic radius.

Speaker: Clayton Robertson, Univ. of Louisville