Using M Dwarf Spectra to Map Extinction in the Local Galaxy

TL;DR

This study uses spectra from over 56,000 M dwarfs in SDSS to create detailed extinction and R_V maps of the local Galaxy, improving distance estimates and revealing dust structure.

Contribution

It introduces a spectral fitting method across the full optical range to map extinction and R_V, providing higher resolution and accuracy than previous two-color methods.

Findings

Extinction map extends to ~2 kpc from the Sun.

R_V values are consistent with the diffuse ISM value of 3.1.

Dust scale height is estimated at 119±15 parsecs.

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 {\AA} 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 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\pm15 parsecs and find evidence for a local dust cavity.