Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13

TL;DR

This study uses high-resolution JVLA and GBT observations to analyze the kinematic and density structure of the SDC13 infrared dark hub, revealing gravitational fragmentation and the role of filament junctions in core formation.

Contribution

It provides new insights into the gravitational processes driving filament fragmentation and core formation in the SDC13 hub, highlighting the importance of hub morphology and gravitational energy conversion.

Findings

All four filaments are thermally super-critical, indicating gravitational instability.

Fragmentation occurs with cores separated by ~0.37 pc, consistent with gravitational instabilities.

Massive cores are located at filament junctions with high velocity dispersions.

Abstract

Converging networks of interstellar filaments i.e. hubs, have been recently linked to the formation of stellar clusters and massive stars. The goal is to study the kinematic and density structure of the SDC13 hub at high angular resolution to determine what drives its evolution and fragmentation. We have mapped SDC13, a 1000Msun infrared dark hub, in NH3(1,1) and NH3(2,2) emission lines, with both the JVLA and GBT down to 0.07pc. The mass-per-unit-lengths of all four hub filaments are thermally super-critical, consistent with the presence of tens of gravitationally bound cores along them. These cores exhibit regular separation of 0.37 +/- 0.16 pc suggesting gravitational instabilities running along these super-critical filaments are responsible for their fragmentation. The observed local increase of the dense gas velocity dispersion towards starless cores is believed to be a consequence of such fragmentation process. We see velocity gradient peaks towards 63% of the cores as expected during the early stages of filament fragmentation. The most massive cores are located at the filament junctions, where the velocity dispersion is the largest. We interpret this as the result of the hub morphology generating the largest acceleration gradients near the hub centre. We propose a scenario for the evolution of the SDC13 hub in which filaments first form as post-shock structures in a supersonic turbulent flow. Then gravity takes over and starts shaping the evolution of the hub, both fragmenting filaments and pulling the gas towards the centre of the gravitational well. By doing so, gravitational energy is converted into kinetic energy in both local (cores) and global (hub centre) potential well minima. Furthermore, the generation of larger gravitational acceleration gradients at the filament junctions promotes the formation of more massive cores. [abridged]