Using M Dwarf Spectra to Map Extinction in the Local Galaxy
Abstract
We use spectra of more than 56,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) to create a high-latitude extinction map of the local Galaxy. Our technique compares spectra from the stars in the SDSS Data Release 7 M dwarf sample in low-extinction lines of sight, as determined by Schlegel, Finkbeiner, & Davis, to other SDSS M dwarf spectra in order to derive improved distance estimates and accurate line-of-sight extinctions. Unlike most previous studies, which have used a two-color method to determine extinction, we fit extinction curves to fluxes across the entire spectral range from 5700 to 9200 for every star in our sample. Our result is an extinction map that extends from a few tens of pc to approximately 2 kpc away from the sun. We also use a similar technique to create a map of RV values within approximately 1 kpc of the sun, and find they are consistent with the widely accepted diffuse interstellar medium value of 3.1. Using our extinction data, we derive a dust scale height for the local galaxy of 11915 parsecs and find evidence for a local dust cavity.