Star Formation in the NE-Circinus Molecular Cloud Complex

Abstract

This paper presents the first dedicated characterisation of the NE-Circinus Complex (TGU H1984, DCld 320.7−03.6), a previously unstudied star-forming dark cloud complex serendipitously identified in archival Herschel SPIRE observations targeting the foreground Bok globules BHR 99 and BHR 100. Using Herschel SPIRE photometry, Planck Galactic Cold Clumps data, near-infrared 2MASS colour excess mapping, AllWISE photometry, Gaia DR3 photometry, and a three-dimensional dust extinction map, the complex and its embedded YSO population are characterised for the first time. Two independent photometric methods place the complex at 750 ± 50 pc. Three morphologically distinct components are identified: a dense main cloud body, a diffuse eastern component, and a northern filamentary extension. The main cloud body has a SPIRE-derived dust temperature of 14.5 ± 0.5 K. Near-infrared H − K colour excess mapping yields a core gas mass of ∼277 M⊙ and a total gas mass of ∼439 M⊙, consistent with the Planck PGCC column density. An AllWISE YSO census identifies 39 candidates across all three components, confirming active star formation throughout the complex. Multi-epoch NEOWISE-R photometry reveals three significantly variable sources, including one aperiodic dipper — a previously uncatalogued YSO exhibiting dimming consistent with inner-disc occultation. Two previously uncatalogued compact Bok globules are identified on the western edge of the northern extension, both detected in SPIRE continuum emission. That this complex went uncharacterised despite Herschel data being publicly available since 2013 underscores the scientific value of archival examination and the incomplete state of southern sky molecular cloud inventories.