Burton, M. G. et al., 2006, IAU Special Session, 7, 20 | View on ADS (2006IAUSS...7E..20B)
The proposed High Elevation Antarctic Terahertz Telescope (HEAT) is an instrument designed for the measurement of sub-mm spectral lines over regions several square degrees in size toward the Milky Way and Magellanic Clouds. By mapping as a function of Galactic position the size and mass distribution and internal velocity dispersion of interstellar clouds in the Galaxy in both atomic and molecular lines, HEAT will construct the first barometric map of the Galactic Plane. HEAT will also map the gas heating rate, the star formation rate and produce the first large scale Galactic images of the dominant cooling atomic cooling lines of carbon and nitrogen. balance, and evolution of molecular clouds in the Milky Way and distant star-forming galaxies. Since the ionisation potential of nitrogen is 14.5eV, the 1461.1319 GHz = 205.176µm line of [NII] arises from regions where hydrogen is ionised, and thus serves as an extinction-free probe of the Warm Ionised Medium (WIM). There is an observed nonlinear relationship between [CII] and [NII] emission (Bennett et al. 1994) on large scales. By observing a variety of UV-illuminated giant molecula clouds, compact and diffuse HII regions, and planetary nebulae in the 1461 GHz [NII] line at 700 times the spectral and angular resolution of satellite data, the [CII]/[NII] intensity ratio can be used as a probe to determine how much of the Galaxy's [CII] emission arises in ionised gas.