The JCMT Gould Belt Survey: A Quantitative Comparison Between SCUBA-2 Data Reduction Methods

TL;DR

This study compares two data reduction methods for SCUBA-2 submillimetre observations, highlighting their suitability for different astrophysical analyses and emphasizing the importance of parameter choices in data processing.

Contribution

It provides a quantitative comparison of two reduction methods, demonstrating how parameter tuning affects the recovery of compact and extended astronomical structures.

Findings

GBS LR1 recovers compact sources at low brightness levels

JCMT LR1 is better for detecting compact emission presence

Extended structures require careful boundary setting to avoid errors

Abstract

Performing ground-based submillimetre observations is a difficult task as the measurements are subject to absorption and emission from water vapour in the Earth's atmosphere and time variation in weather and instrument stability. Removing these features and other artifacts from the data is a vital process which affects the characteristics of the recovered astronomical structure we seek to study. In this paper, we explore two data reduction methods for data taken with the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) at the James Clerk Maxwell Telescope (JCMT). The JCMT Legacy Reduction 1 (JCMT LR1) and The Gould Belt Legacy Survey Legacy Release 1 (GBS LR1) reduction both use the same software, Starlink, but differ in their choice of data reduction parameters. We find that the JCMT LR1 reduction is suitable for determining whether or not compact emission is present in a given region and the GBS LR1 reduction is tuned in a robust way to uncover more extended emission, which better serves more in-depth physical analyses of star-forming regions. Using the GBS LR1 method, we find that compact sources are recovered well, even at a peak brightness of only 3 times the noise, whereas the reconstruction of larger objects requires much care when drawing boundaries around the expected astronomical signal in the data reduction process. Incorrect boundaries can lead to false structure identification or it can cause structure to be missed. In the JCMT LR1 reduction, the extent of the true structure of objects larger than a point source is never fully recovered.