GLOSTAR · A Global View of Star Formation in the Milky Way

Stars with more than about ten solar masses dominate galactic ecosystems and understanding the circumstances of their formation is one of the great challenges of modern astronomy. The spectacular HII regions they excite delineate the spiral arms of galaxies such as our own when seen face on making it clear that star formation and Galactic structure are intimately related. We propose to attain a Global View of Star Formation in the Milky Way in a powerful multi-pronged approach. Using VLBI observations of maser sources associated with young protostars, we will measure distances by trigonometric parallax to most of the dominant star forming regions in the Galaxy, which will reveal its spiral structure as well as faithfully represent the luminosity and masses of its constituents. A survey for submillimeter emission from dust, which we are presently pursuing, will deliver the locations of unseen deeply embedded protostars and protoclusters. We plan to combine this data with a comprehensive program to study the gaseous content of the protostellar regions and a very sensitive survey of the Galactic plane with the newly Expanded Very Large Array to find masers and hypercompact HII regions, pinpointing the very centers of the earliest star-forming activity. We also propose to study the infrared emission from more developed massive star clusters, deriving distance with the classic spectro-photometric method, properly calibrated with trigonometric parallaxes, and for the first time adapted to an extensive IR dataset. Our synoptic approach will utilize Europe s premier telescopes including ESO s VLT, the European VLBI Network, the APEX telescope, and ALMA to create a coherent, unique dataset with true legacy value for a global perspective on star formation in our Galaxy.