This dust extinction technique provides us with gas surface density maps at an unprecedented resolution for full disc coverage studies of nearby galaxies. When assuming the same dust opacity law, our technique produces surface densities that are consistent with independent studies. We find that discrepancies between our estimates of surface density and other studies stem primarily from the choice of dust model (i.e. Our dust (and gas) surface density map is consistent with independent dust- and CO-based studies at lower resolution. Here, we apply this technique to M51 (NGC 5194) as a proof-of-concept, obtaining a resolution of 0.14 arcsec (5 pc). The contribution of foreground light along the line-of-sight is calibrated using dust emission observations, assuming that the dust sits in a layer close to the mid-plane of the face-on galaxy. The method measures the dust attenuation in optical bands on a pixel-by-pixel basis against a smoothed, reconstructed stellar distribution. We present a new dust extinction technique with which we are able to retrieve parsec-scale gas surface density maps for entire nearby galaxies.
