JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: II. SCUBA-2 850$mu$m data reduction and dust flux density catalogues

We present the SCUBA-2 850 mu m component of JINGLE, the new JCMT large survey for dust and gas in nearby galaxies, which with 193 galaxies is the largest targeted survey of nearby galaxies at 850 mu m. We provide details of our SCUBA-2 data reduction pipeline, optimized for slightly extended sources, and including a calibration model adjusted to match conventions used in other far-infrared (FIR) data. We measure total integrated fluxes for the entire JINGLE sample in 10 infrared/submillimetre bands, including all WISE, Herschel-PACS, Herschel-SPIRE, and SCUBA-2 850 mu m maps, statistically accounting for the contamination by CO(J = 3-2) in the 850 mu m band. Of our initial sample of 193 galaxies, 191 are detected at 250 mu m with a >= 5 sigma significance. In the SCUBA-2 850 mu m band we detect 126 galaxies with >= 3 sigma significance. The distribution of the JINGLE galaxies in FIR/sub-millimetre colour-colour plots reveals that the sample is not well fit by single modified-blackbody models that assume a single dust-emissivity index (beta). Instead, our new 850 mu m data suggest either that a large fraction of our objects require beta < 1.5, or that a model allowing for an excess of sub-mm emission (e.g. a broken dust emissivity law, or a very cold dust component less than or similar to 10 K) is required. We provide relations to convert FIR colours to dust temperature and beta for JINGLE-like galaxies. For JINGLE the FIR colours correlate more strongly with star-formation rate surface-density rather than the stellar surface-density, suggesting heating of dust is greater due to younger rather than older stellar-populations, consistent with the low proportion of early-type galaxies in the sample.