Vol. 610
In section 6. Interstellar and circumstellar matter

An ALMA study of the Orion Integral Filament. I. Evidence for fibers in a massive cloud

by A. Hacar, M. Tafalla, J. Forbrich, et al. A&A 610, A77


The authors combined two new ALMA Cycle 3 mosaics with previous IRAM 30m observations to produce a high-dynamic range N2H+ (1-0) emission map of the Orion integral filament that traces its high-density material and velocity structure down to scales of 0.009 pc (approx. 2000 au). From the analysis of the gas kinematics, the authors identify a total of 55 dense fibers in the central region of the Orion filament. These fibers are characterized by transonic internal motions, lengths of ∼ 0.15 pc, and masses per-unit-length close to those expected in hydrostatic equilibrium. The fibers form a dense bundle with multiple hub-like associations. Within this complex network, the fibers show a compact radial emission profile with a median FWHM of 0.035 pc, systematically narrower than the previously proposed universal 0.1 pc filament width. These observations suggest strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. In particular, the fibers show identical dynamic properties in both low- and high-mass regions. While their origin remains under debate, the formation of transonic fibers appears to be an inherent property of the interstellar medium turbulence and an essential ingredient of the star formation process in both low- and high-mass regions.