Abstract
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 side effect 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 we 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 M31, which contaminates the 850 μm band. We find that while normally the contamination is below our sensitivity limit, it 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.
Highlights
The Andromeda galaxy (Messier 31) is possibly the most frequently observed galaxy in the sky
We found a = 0, b = 1.04, showing the SCUBA-2 data-reduction pipeline had slightly underestimated the random errors in the fluxes, and that f = 0.12, showing that there is a systematic error that depends on the brightness of the emission, confirming the qualitative impression produced by Figure 11
We have presented submillimeter images of the Andromeda galaxy obtained at 450 and 850 μm, the first images made from the ground that properly represent the structure of the galaxy on all spatial scales
Summary
The Andromeda galaxy (Messier 31) is possibly the most frequently observed galaxy in the sky. Andromeda has a larger bulge (Yin et al 2009), less obvious spiral arms (Gordon et al 2006; Kirk et al 2015), and much of the star formation in the galaxy is occurring in a large ring (Ford et al 2013) The cause of this ring is unknown. One interesting suggestion is that the ring may be the result of the dwarf galaxy M32 passing through the center of the disk, generating a density wave, and a wave of star birth that propagates outward through the disk (Block et al 2006) This seems unlikely since the star formation history in the disk has no obvious radial gradient (Lewis et al 2015), and the cause of the ring remains a mystery
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