The HASHTAG project: The First Submillimeter Images of the Andromeda
  Galaxy from the Ground
  Observing nearby galaxies with submillimeter telescopes on the ground has two
major challenges. First, the brightness is significantly reduced at long
submillimeter wavelengths compared to the brightness at the peak of the dust
emission. Second, it is necessary to use a high-pass spatial filter to remove
atmospheric noise on large angular scales, which has the unwelcome by-product
of also removing the galaxy's large-scale structure. We have developed a
technique for producing high-resolution submillimeter images of galaxies of
large angular size by using the telescope on the ground to determine the
small-scale structure (the large Fourier components) and a space telescope
(Herschel or Planck) to determine the large-scale structure (the small Fourier
components). Using this technique, we are carrying out the HARP and SCUBA-2
High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international
Large Program on the James Clerk Maxwell Telescope, with one aim being to
produce the first high-fidelity high-resolution submillimeter images of
Andromeda. In this paper, we describe the survey, the method we have developed
for combining the space-based and ground-based data, and present the first
HASHTAG images of Andromeda at 450 and 850um. We also have created a method to
predict the CO(J=3-2) line flux across M31, which contaminates the 850um band.
We find that while normally the contamination is below our sensitivity limit,
the contamination can be significant (up to 28%) in a few of the brightest
regions of the 10 kpc ring. We therefore also provide images with the predicted
line emission removed.
