Dynamics of cluster-forming hub-filament systems. The case of the high-mass star-forming complex Monoceros R2
Schneider, N.; Tremblin, P.; Didelon, P.; García-Burillo, S.; Goicoechea, J. R.; Luna, A.; Kramer, C.; Pilleri, P.; Fuente, A.; Hennebelle, P.; Kainulainen, J.; Sánchez-Monge, Á.; Suri, S.; Ballesteros-Paredes, J.; Geen, S.; González-García, M.; Treviño-Morales, S. P.; Lee, Y. -N.
Sweden, Spain, Germany, France, Mexico
Abstract
Context. High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest of these systems, making it an excellent target for case studies.
Aims: We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system.
Methods: We employed observations of the 13CO and C18O 1 →0 and 2 →1 lines obtained with the IRAM-30 m telescope. We also used H2 column density maps derived from Herschel dust emission observations.
Results: We identified the filamentary network in Mon R2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament). The main filaments have line masses of 30-100 M⊙ pc-1 and show signs of fragmentation, while the secondary filaments have line masses of 12-60 M⊙ pc-1 and show fragmentation only sporadically. In the context of Ostriker's hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are transcritical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10-4-10-3 M⊙ yr-1 into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1-0.4 × 10-4 M⊙ yr-1. The main filaments extend into the central hub. Their velocity gradients increase toward the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is 2.5 Myr, ten times longer than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring- or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.