EPoS Contribution
EPoS Contribution
Gravity Drives the Evolution of Infrared Dark Hubs

Gwen Williams
U St. Andrews, St. Andrews, UK
It is now widely considered that interstellar filaments are the archetypal intermediate stage in the star formation process. The vast majority of cores (the direct progenitors of stars) sit on top of the densest filaments. Yet a number of questions remain regarding the physics that govern their formation and evolution. Studies of infrared dark clouds (IRDCs) help shed light on this, as they are thought to contain the pristine fingerprints of the initial conditions of star formation.
We present a multi-scale study of the SDC13 IRDC hub filament system. SDC13 contains 1000 Msun of material, resides 3.6kpc away in the galactic plane, and has a remarkable morphology, containing 4 parsec-long filaments that spatially converge on a central hub region. Overall, SDC13 is an ideal target to study how filaments form, fragment and dynamically interact with each other.
In combining NH3 emission data from the JVLA interferometer and the GBT single-dish telescope, we studied the evolution of SDC13 down to 0.07pc spatial scales. We propose a scenario for the evolution of the SDC13 hub in which the filaments first form as post-shock structures in a supersonic turbulent flow. As a result of the turbulent energy dissipation in the shock, the dense gas within the filaments is predominantly sub-sonic. Then gravity takes over and starts shaping the evolution of the hub, fragmenting filaments and pulling the gas towards the centre of the gravitational well. By doing so, gravitational energy is converted into kinetic energy in local cores (where we see the gas velocity dispersion increase towards 73% of starless cores) and global hub centre potential well minima. This generates more massive cores at the hub centre as a result of larger acceleration gradients due to the hub morphology itself.
We also studied C18O(1-0) and 13CO(1-0) data from the IRAM 30m, achieving 0.15km/s spectral resolution, to constrain the SDC13 filament formation process. In recent years, velocity-coherent sub-filaments (termed fibers) have been suggested to represent a specific turbulence-dominated mode of filament formation. Position-velocity slices along the SDC13 filaments do not reveal the presence of fibers. In conjunction with the NH3 data results, it is suggested that the dominance of gravity as a direct result of the hub morphology itself suppresses fiber formation. On the other hand, this may indicate that fibers are not archetypical constituents of the interstellar medium, and are unique to regions such as Taurus.
Caption: (a) The H2 column density map of SDC13, calculated from the integrated intensity of NH3 emission from the JVLA and GBT. The four distinct filaments converging on the central hub are clearly visible. (b) The mean velocity width at starless core positions (in km/s). The left panel plots the cores with peaks in velocity width, whilst the right panel plots the cores without velocity width peaks. This direct comparison of the two core types shows the velocity width in the peaked cores is on average 1.4 times greater than in the other, non-peaked cores. Overplotted contours are of the mean H2 column density.
Collaborators:
N. Peretto, Cardiff U, UK
A. Avison, U Manc., UK
A. Duarte-Cabral, Cardiff U, UK
G. Fuller, U Manchester, UK
Suggested Session: Filaments