The THOR project is a northern Galactic plane survey (15 < l < 67deg and |b| < +-1deg) in HI, four OH, and 19 H alpha recombination lines as well as in the L-band continuum from 1 to 2GHz. The spatial resolution of the Very Large Array (VLA) in the C-array of about 20'' is essential for comparison with other Galactic plane surveys. This large multi-line and continuum Galactic plane survey addresses a plethora of scientific topics. Among them, we study the dynamics of the interstellar medium and cloud formation from the atomic to the molecular phase, and directly compare the results to theoretical cloud formation models. OH and HI absorption/emission line studies enable detailed investigations of the cold phases of the interstellar medium. Combining the data with Herschel/SOFIA C+ observations reveals the nature of photodissociation regions. The HII region recombination lines allow us to study, e.g., the dynamics of potentially triggered star formation, and to derive kinematic distances. In addition to that, unexpected exciting results will emerge from such a novel survey. The THOR survey provides a VLA legacy product available to a wide astronomical community.

The Jansky Very Large Array (VLA) where all THOR data are taken.