Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites

Abstract: We present the first Herschel PACS and SPIRE results of the Vela C molecular complex in the far-infrared and submillimetre regimes at 70, 160, 250, 350, and 500 um, spanning the peak of emission of cold prestellar or protostellar cores. Column density and multi-resolution analysis (MRA) differentiates the Vela C complex into five distinct sub-regions. Each sub-region displays differences in their column density and temperature probability distribution functions (PDFs), in particular, the PDFs of the Centre-Ridge' andSouth-Nest' sub-regions appear in stark contrast to each other. The Centre-Ridge displays a bimodal temperature PDF representative of hot gas surrounding the HII region RCW 36 and the cold neighbouring filaments, whilst the South-Nest is dominated by cold filamentary structure. The column density PDF of the Centre-Ridge is flatter than the South-Nest, with a high column density tail, consistent with formation through large-scale flows, and regulation by self-gravity. At small to intermediate scales MRA indicates the Centre-Ridge to be twice as concentrated as the South-Nest, whilst on larger scales, a greater portion of the gas in the South-Nest is dominated by turbulence than in the Centre-Ridge. In Vela C, high-mass stars appear to be preferentially forming in ridges, i.e., dominant high column density filaments.

Filaments and Ridges in the Vela C Molecular Complex: Insights from Herschel Observations

The paper under review provides an in-depth analysis of the Vela C molecular complex, utilizing data from the Herschel Space Observatory, with a focus on the formation of low-to-high mass stars. The study leverages observations in the far-infrared and submillimetre regimes to investigate the structural diversity within the complex, revealing distinct sub-regions with varying star-forming potential.

Observational Data and Methodology

The research employs the PACS and SPIRE instruments on board Herschel, covering wavebands at 70, 160, 250, 350, and 500 µm. The focus is on capturing emission from cold prestellar and protostellar cores across a 3 square degree field. The authors effectively employ multi-resolution analysis (MRA) and column density and temperature probability distribution functions (PDFs) to segregate Vela C into five sub-regions—North, Centre-Ridge, Centre-Nest, South-Ridge, and South-Nest. These regions exhibit distinct characteristics in terms of structure and star formation activity.

Key Findings

1. Sub-Region Characteristics:

   • The Centre-Ridge is notable for its bimodal temperature PDF, indicative of both hot gas around HII region RCW 36 and cool dense filaments.
   • In contrast, the South-Nest is characterized predominantly by cold filamentary structures.
   • The Centre-Ridge also displays a flatter column density PDF, suggesting its formation is influenced significantly by large-scale flows and is regulated by self-gravity.

2. Filamentary Structures:

   • Filaments play a central role in star formation within Vela C, with the study identifying dense filamentary ridges as potential sites for high-mass star formation.
   • The research spotlights two ridges, Centre-Ridge and South-Ridge, which demonstrate a higher concentration of matter and structural differences when compared to other filaments.

3. Massive Star Formation Preference:

   • High-mass stars in Vela C seem to preferentially form in ridges, particularly those with high column densities, such as Centre-Ridge. The authors discuss a potential column density threshold for high-mass star formation, aligning with the theoretical framework proposed by Krumholz and McKee, where only regions with column densities exceeding 1 g/cm² can host massive stars.

Implications and Future Directions

The study's findings enhance the understanding of the conditions and environments conducive to various modes of star formation within molecular clouds. By dissecting the sub-regions of Vela C, the paper contributes insights into the processes that contribute to the structural and functional differentiation in star-forming regions.

From a theoretical perspective, the results underscore the complexity of star formation mechanisms, suggesting that both turbulence and gravity play crucial roles at different scales. Practically, the study indicates the necessity of high-resolution observations across multiple wavelengths to accurately map molecular clouds and identify potential star formation sites.

Future research should continue to refine the understanding of threshold conditions necessary for high-mass star formation and further investigate the dynamics within filamentary structures. Additionally, integrating these observational results with numerical simulations could provide a more comprehensive model of star formation processes across varying environments and scales in the interstellar medium.