Abstract
In the next three years, surveys of the Northern and Southern skies using focal plane arrays on aperture synthesis radio telescopes will lead to a breakthrough in our knowledge of the warm and cool atomic phases of the interstellar medium and their relationship with the diffuse molecular gas. The sensitivity and resolution of these surveys will give an order of magnitude or more improvement over existing interstellar medium data. The GASKAP (South) and GAMES (North) projects together constitute a complete survey of the Milky Way plane and the Magellanic Clouds and Stream in both emission and absorption in the H I 21-cm line and the OH 18-cm lines. The overall goal of this project is to understand the mechanism of galaxy evolution, through a detailed tracing of the astrophysical processes that drive the cycle of star formation in very different environments. Comparison of 21-cm emission and absorption highlights the transition from the warm, diffuse medium to cool clouds. Tracing turbulence in the Magellanic Stream shows how extra-galactic gas makes the difficult passage through the halo to replenish the disk. Finally, high resolution images of OH masers trace outflows from evolved stars that enrich the medium with heavy elements. To understand how the Milky Way was assembled and how it has evolved since, the speed and efficiency of these processes must be measured, as functions of Galactic radius and height above the plane. Observations of similar processes in the Magellanic Clouds show how differently they might have worked in conditions typical of the early universe.
Highlights
In the three years, surveys of the Northern and Southern skies using focal plane arrays on aperture synthesis radio telescopes will lead to a breakthrough in our knowledge of the warm and cool atomic phases of the interstellar medium and their relationship with the diffuse molecular gas
The GASKAP (South) and GAMES (North) projects together constitute a complete survey of the Milky Way plane and the Magellanic Clouds and Stream in both emission and absorption in the H I 21-cm line and the OH 18-cm lines
The overall goal of this project is to understand the mechanism of galaxy evolution, through a detailed tracing of the astrophysical processes that drive the cycle of star formation in very different environments
Summary
Surveys of the 21-cm emission of the Milky Way were begun in the early 1950’s, Oort et al (1958) and made great progress through the 1960’s and 1970’s, (reviewed by Burton, 1988). The most comprehensive surveys of the sky that have been fully stray-radiation corrected are the LAB survey, Kalberla et al ( 2005) with resolution 35., and more recently the combined GASS and EBHIS surveys, McClure-Griffiths et al (2009); Kalberla et al (2010); Kerp et al (2011), which combine data from the Parkes (resolution 14.) and Effelsburg (10.) telescopes. These telescopes give the highest resolution possible for surveys of the entire sky, but the Arecibo telescope can give higher resolution over a significant portion of the sky (36◦ > > 4◦), and the GALFA survey has made very sensitive spectral line cubes of most of this area with beamwidth 3.5. The gas in the MCs has high enough column density that it shows brightness temperatures as high as 135 K, Kim et al (2003), but in the MS typical column densities are a factor ten to 100 lower, so high sensitivity is required to map the Stream (Trms < 0.5 K)
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