The HASHTAG Project: the first submillimeter images of the Andromeda galaxy from the ground
Astrophysical Journal Supplement IOP Science 257 (2021) 52
Authors:
Martin Bureau, Dimitra Rigopoulou
Abstract:
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 850 µm. We also have created a method
to predict the CO(J=3–2) line flux across M 31, which contaminates the 850 µm 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.
