The SCUBA HAlf degree extragalactic survey -: VI.: 350-μm mapping of submillimetre galaxies

A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 mu m has been carried out to map the regions around several 850-mu m-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-mu m flux densities for 24 850-mu m sources, seven of which are detected at >= 2.5 sigma within a 10 arcsec search radius of the 850-mu m positions. When results from the literature are included the total number of 350-mu m flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich (M(dust) similar or equal to 9 x 10(8) M(circle dot)), luminous (L(FIR) similar or equal to 2 x 10(12) L(circle dot)) star-forming galaxies with intrinsic dust temperatures of similar or equal to 35 K and star formation rates of similar or equal to 400 M(circle dot) yr(-1). We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-mu m source counts, N(350)(> 25 mJy) similar to 200-500 deg(-2).