The JCMT Gould Belt Survey: a first look at Southern Orion A with SCUBA-2

Abstract

We present the JCMT Gould Belt Survey’s first look results of the southern extent of the Orion A Molecular Cloud (δ ≤ −5:31:27.5). Employing a two-step structure identification process, we construct individual catalogues for large-scale regions of significant emission labelled as islands and smaller-scale subregions called fragments using the 850 µm contin- uum maps obtained using SCUBA-2. We calculate object masses, sizes, column densities, and concentrations. We discuss fragmentation in terms of a Jeans instability analysis and highlight interesting structures as candidates for follow-up studies. Furthermore, we associate the detected emission with young stellar objects (YSOs) identified by Spitzer and Herschel. We find that although the population of active star-forming regions contains a wide variety of sizes and morphologies, there is a strong positive correlation between the concentration of an emission region and its calculated Jeans instability. There are, however, a number of highly unstable subregions in dense areas of the map that show no evidence of star formation. We find that only ∼72 per cent of the YSOs defined as Class 0+I and flat-spectrum protostars
coincide with dense 850 µm emission structures (column densities >3.7 × 1021 cm−2). The remaining 28 per cent of these objects, which are expected to be embedded in dust and gas,
may be misclassified. Finally, we suggest that there is an evolution in the velocity dispersion of YSOs such that sources which are more evolved are associated with higher velocities.