Dynamics of cluster-forming hub-filament systems. The case of the high-mass star-forming complex Monoceros R2

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. <BR /> Aims: We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. <BR /> Methods: We employed observations of the <SUP>13</SUP>CO and C<SUP>18</SUP>O 1 →0 and 2 →1 lines obtained with the IRAM-30 m telescope. We also used H<SUB>2</SUB> column density maps derived from Herschel dust emission observations. <BR /> 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<SUB>☉</SUB> pc<SUP>-1</SUP> and show signs of fragmentation, while the secondary filaments have line masses of 12-60 M<SUB>☉</SUB> pc<SUP>-1</SUP> 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<SUP>-4</SUP>-10<SUP>-3</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP> into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1-0.4 × 10<SUP>-4</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP>. 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.