The HASHTAG Project: the first submillimeter images of the Andromeda galaxy from the ground
Bureau, M, Williams, TG, Smith, WL, Rigopoulou, D, Eales, SA
Abstract
Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges.\nFirst, 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\natmospheric noise on large angular scales, which has the unwelcome by-product of also removing the\ngalaxy’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\nsmall-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\nout the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an\ninternational Large Program on the James Clerk Maxwell Telescope, with one aim being to produce\nthe first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe\nthe survey, the method we have developed for combining the space-based and ground-based data, and\npresent the first HASHTAG images of Andromeda at 450 and 850 µm. We also have created a method\nto predict the CO(J=3–2) line flux across M 31, which contaminates the 850 µm band. We find that\nwhile normally the contamination is below our sensitivity limit, the contamination can be significant\n(up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with\nthe predicted line emission removed.