First-generation Science Cases for Ground-based Terahertz Telescopes
  Ground-based observations at terahertz (THz) frequencies are a newly
explorable area of astronomy for the next ten years. We discuss science cases
for a first-generation 10-m class THz telescope, focusing on the Greenland
Telescope as an example of such a facility. We propose science cases and
provide quantitative estimates for each case. The largest advantage of
ground-based THz telescopes is their higher angular resolution (~ 4 arcsec for
a 10-m dish), as compared to space or airborne THz telescopes. Thus,
high-resolution mapping is an important scientific argument. In particular, we
can isolate zones of interest for Galactic and extragalactic star-forming
regions. The THz windows are suitable for observations of high-excitation CO
lines and [N II] 205 um lines, which are scientifically relevant tracers of
star formation and stellar feedback. Those lines are the brightest lines in the
THz windows, so that they are suitable for the initiation of ground-based THz
observations. THz polarization of star-forming regions can also be explored
since it traces the dust population contributing to the THz spectral peak. For
survey-type observations, we focus on ``sub-THz'' extragalactic surveys, whose
uniqueness is to detect galaxies at redshifts z ~ 1--2, where the dust emission
per comoving volume is the largest in the history of the Universe. Finally we
explore possibilities of flexible time scheduling, which enables us to monitor
active galactic nuclei, and to target gamma-ray burst afterglows. For these
objects, THz and submillimeter wavelength ranges have not yet been explored.
