Release and Analysis of the Galactic Ring Survey

Trustees Of Boston University, Boston

Investigators

Abstract

AST 0507657 Jackson The Milky Way's dominant star-forming structure, the 5 kpc ring, remains largely unexplored. New advances in mm-wave array technology permit a fresh examination of the 5 kpc ring. Using the new SEQUOIA multipixel array receiver on the FCRAO 14 m telescope, Dr. James Jackson and colleagues are conducting a new molecular line survey of the inner Galaxy, the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (GRS). The GRS is an ambitious survey designed to map the inner Galaxy and especially the 5 kpc ring in 13CO. When the data-taking is complete in April 2005, they will have mapped over 72 square degrees of the Inner Galaxy. They have established efficient mapping strategies, automated the data reduction, and begun the scientific analysis. This award will be used to prepare and release the data to the community and to conduct scientific investigations. A particularly exciting GRS discovery was the identification of Infrared Dark Clouds as the cold, dense precursors to massive star-forming regions. Compared with previous molecular line surveys of the inner Galaxy, the GRS offers excellent sensitivity (0.4 K), better spectral resolution (0.21 km/s), the same or better angular resolution (46"), better sampling (22"), and the use of 13CO (1-0), a better column density tracer than 12CO. All GRS data will be made available to the astronomical community. By minimizing velocity-crowding through the use of 13CO, they can isolate, identify, and catalog molecular clouds and cloud cores throughout the 5 kpc ring. Because the 22" sampling rate is so fine, they will better determine the structures of these clouds. Moreover, they have found that 21 cm H I selfabsorption features toward GRS molecular clouds allow one to resolve the long-standing near/far kinematic distance ambiguity. Because they can measure the distances to clouds and their embedded infrared young stellar objects and star clusters, they can for the first time establish their masses, sizes, distributions, and luminosities. With the new MSX and Spitzer infrared surveys, the research team can determine the luminosities, distances, and distribution of embedded young stellar objects throughout the inner Galaxy. They will complete five key science projects in this funding period: o Cataloging molecular clouds and cloud cores discovered by the GRS. o Establishing kinematic distances to molecular clouds and their embedded infrared star-forming regions. o Determining the structure of the inner Milky Way, and especially that of the 5 kpc ring. o Quantifying and testing models of the internal structure of molecular clouds. o Probing the internal structure of Infrared Dark Clouds to study the very earliest phases of cluster formation. When complete in 2005, the GRS will be the definitive map of the molecular gas distribution in the Inner Galaxy. Because the GRS team will consist of postdocs, graduate students, and undergraduates, the GRS will help train the next generation of astronomers and programmers. It is unlikely that the GRS will be surpassed in either sensitivity or areal coverage in the next 20 years, since it will be technically infeasible to conduct large-area surveys with the new suite of planned large-aperture single dish telescopes or interferometers. Like the Palomar and Sloan Surveys, the GRS will be a vital, unique resource for generations of Galactic astronomers. Its panoramic 13CO map will be the finding chart for an enormous amount of future Milky Way research.