Event

Most observations of the Milky Way's gas and dust are limited to two dimensions; their angular distribution is precisely measured, but their distribution in distance is much more uncertain.  Large surveys of stars can be used to resolve this uncertainty.  Because light from stars is absorbed and scattered by intervening material before observation on earth, the Galaxy's stars can be used as a dense network of lighthouses to illuminate the structure and properties of the Milky Way's interstellar medium.  In this talk, I'll describe our ongoing program to use large surveys to map the interstellar medium in three dimensions.  We have mapped the dust column over the nearest ~5 kpc at unprecedented resolution, highlighting complex networks of diffuse voids and dense star-forming regions.  We have also been able to measure the size distribution of dust grains throughout the Milky Way, revealing kiloparsec-scale structures that may track variations in the Galactic star-formation rate and gas density.  Numerous other projects are possible, for example studying the 3D kinematics of the Milky Way's gas (through diffuse interstellar bands) and the structure of the Galaxy's magnetic field (through starlight and dust emission polarization).  Dust also has important applications to cosmology through its reddening of supernovae and its thermal emission at microwave frequencies.  Upcoming surveys and instruments like Gaia, SDSS-V, LSST, and JWST promise a bright future for 3D studies of the interstellar medium, offering incredibly accurate distance measurements, order-of-magnitude larger samples of stars, and unrivalled sensitivity.