Protostars and Planets VI, Heidelberg, July 15-20, 2013
CO gas kinematics and excitation in a filamentary IRDC: Filament-filament interaction and accretion processes.
Jimenez-Serra, Izaskun (European Southern Observatory, Germany)
Caselli, Paola (University of Leeds, UK)
Fontani, Francesco (Osservatorio Astrofisico di Arcetri, Italy)
Tan, Jonathan C. (University of Florida, USA)
Henshaw, Jonathan D. (Universiity of Leeds, UK)
Kainulainen, Jouni (Max-Planck-Institute for Astronomy, Germany)
Hernandez, Audra K. (University of Wisconsin-Madison, USA)
Some theories of molecular cloud formation propose that molecular clouds form in highly dynamical environments characterized by the interaction of converging gas flows or cloud-cloud collisions. The determination of the dynamics and physical conditions of the molecular gas in clouds at the early stages of their evolution is thus essential to establish the dynamical imprints of such collisions, and to infer the physical processes involved in their formation. We present large-scale (~1.7pc x 3.4 pc) multi-transition 13CO and C18O on-the-fly maps carried out with the IRAM 30m and JCMT telescopes toward the Infrared-Dark Cloud G035.39-00.33. This cloud shows a very filamentary structure and relatively little star formation activity, suggestive of its youth, and where evidence for a flow-flow collision has recently been reported. Consistent with previous studies, the 13CO and C18O line maps toward G035.39-00.33 reveal that the molecular gas in this cloud is distributed in three different filaments separated in velocity space by ~3 kms-1 (Filaments 1, 2 and 3). The massive dense cores in this IRDC are preferentially found at the intersecting regions between Filaments 1 and 3, where most of the CO gas is accumulated. The analysis of the 13CO and C18O lines show that the three filaments have a similar kinematic structure with relatively smooth velocity gradients (of ~0.4-0.8 kms-1pc-1) that seem to converge onto core H6, the most massive core in the region located in the center of the IRDC. Several possible scenarios are proposed to explain this velocity gradient, including rotation, global gas accretion along the filaments and large-scale turbulence motions with a steep turbulent power spetrum. The 13CO and C18O gas motions are supersonic across G035.39-00.33 with the line emission showing broader linewidths toward the edges of the IRDC. This may indicate energy dissipation at the densest regions in the IRDC as a consequence of the filament-filament interaction. The excitation analysis of the 13CO gas provides average H2 densities of ~5000-7000 cm-3 for the filaments, with Filaments 2 and 3 being denser and more massive than Filament 1. The C18O J=3-2 and J=2-1 line emission unveils three regions in the IRDC with high CO depletion factors (f_D~5-12), similar to those found in massive starless cores.
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