The JCMT Gould Belt Survey: A First Look at Southern Orion A with SCUBA-2

TL;DR

This study presents initial results from the JCMT Gould Belt Survey on the southern Orion A cloud, analyzing its structure, star formation activity, and the relationship between dense gas and young stellar objects using SCUBA-2 data.

Contribution

It introduces a two-step structure identification process for subregions and provides new insights into the correlation between emission concentration and Jeans instability.

Findings

Strong correlation between emission concentration and Jeans instability.

Approximately 72% of YSOs coincide with dense 850 μm emission regions.

Identification of highly unstable subregions lacking star formation evidence.

Abstract

We present the JCMT Gould Belt Survey's first look results of the southern extent of the Orion A Molecular Cloud ($\delta \leq -5\mathrm{:}31\mathrm{:}27.5$). 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 $\mu$m continuum 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 $\sim$72\% of the YSOs defined as Class 0+I and flat-spectrum protostars coincide with dense 850 $\mu$m emission structures (column densities $>3.7\times10^{21}\mathrm{\:cm}^{-2}$). The remaining 28\% 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 young stellar objects such that sources which are more evolved are associated with higher velocities.