What is controlling the fragmentation process in the Infrared Dark Cloud G14.225-0.506? Differet level of fragmentation in twin hubs

TL;DR

This study investigates the fragmentation process in the infrared dark cloud G14.225-0.506, revealing different fragmentation levels in twin hubs and analyzing the roles of density, turbulence, magnetic fields, and external radiation.

Contribution

It provides a comparative analysis of two hubs within the same IRDC, highlighting that density structure alone does not determine fragmentation levels and suggesting external factors influence fragmentation.

Findings

Hub-S is more fragmented than hub-N.

Density structure is similar in both hubs.

Thermal Jeans fragmentation explains observed fragmentation.

Abstract

We present observations of the 1.3 mm continuum emission toward hub-N and hub-S of the infrared dark cloud G14.225-0.506 carried out with the Submillimeter Array, together with observations of the dust emission at 870 and 350 microns obtained with APEX and CSO telescopes. The large scale dust emission of both hubs consists of a single peaked clump elongated in the direction of the associated filament. At small scales, the SMA images reveal that both hubs fragment into several dust condensations. The fragmentation level was assessed under the same conditions and we found that hub-N presents 4 fragments while hub-S is more fragmented, with 13 fragments identified. We studied the density structure by means of a simultaneous fit of the radial intensity profile at 870 and 350 microns and the spectral energy distribution adopting a Plummer-like function to describe the density structure. The parameters inferred from the model are remarkably similar in both hubs, suggesting that density structure could not be responsible in determining the fragmentation level. We estimated several physical parameters such as the level of turbulence and the magnetic field strength, and we found no significant differences between these hubs. The Jeans analysis indicates that the observed fragmentation is more consistent with thermal Jeans fragmentation compared with a scenario that turbulent support is included. The lower fragmentation level observed in hub-N could be explained in terms of stronger UV radiation effects from a nearby HII region, evolutionary effects, and/or stronger magnetic fields at small scales, a scenario that should be further investigated.