Three-dimensional maps of the interstellar dust extinction curve within the Milky Way galaxy.

Interstellar dust grains cause extinction (absorption and scattering) of light from background astronomical sources. The spectral shape of the extinction curve depends on the dust composition. We used low-resolution optical spectra to measure the extinction curve of 130 million stars. By inverting these data, we mapped the extinction curve parameter R(V) within the Milky Way in three dimensions and within the Magellanic Clouds in two dimensions. These maps provide improved extinction corrections for astronomical observations. We find that R(V) varies with extinction, consistent with dust grains growing by accretion in low-extinction regions and by coagulation in higher-extinction regions. Star-forming regions have high R(V) values, indicating either preferential destruction of small dust grains or additional supply of large dust grains in those regions. Editor's summary: Interstellar dust grains scatter and absorb background light, an effect known as extinction, which is stronger at blue wavelengths than at red wavelengths. How much stronger is quantified by the parameter R(V), which depends on the dust composition and size distribution. Zhang et al. applied machine learning to low-resolution stellar spectra, photometry, and distances to determine R(V) for 130 million stars. They converted the individual R(V) measurements into a three-dimensional map of R(V) within the Milky Way galaxy and two-dimensional maps of the Magellanic Clouds. The results provide information on dust properties and improve extinction corrections for other observations. —Keith T. Smith [ABSTRACT FROM AUTHOR]