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 spectral range from 5700 to 9200 Å for every star in our sample .
Our result is an A _ { V } 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 R _ { V } 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 119 \pm 15 parsecs and find evidence for a local dust cavity .