TUNA Lunch Talk:

I-Jen (Katherine) Lee

University of Illinois

Fragmentation and Kinematics of the Starless Cores in Orion

November 27

12:10PM, Room 230, NRAO, Edgemont Road


We study the structure and kinematics of nine starless cores (0.1 pc) in Orion with the IRAM 30-m telescope and CARMA using CS(2-1) as the main tracer. The sample are chosen from the 850 micron survey with the JCMT (Nutter & Ward-Thompson 2007), with the dust masses ranging from 1 to 50 solar masses. The starless cores mostly show single-peaked emission with the IRAM observations. However, with the high angular resolution CARMA provides, substructures are observed in a majority of the cores with the resolution of 5 arcsecs. This result suggests that hierarchical fragmentation from clouds to cores continues to take place inside the starless cores. By morphologically comparing the structures between the data from IRAM, CARMA and Herschel 500 micron images, it is shown that the starless cores and their fragments are formed along the ambient filamentary structures, implying the importance of filamentary structures in the star formation process.

For most of the sources, systematic velocity gradients are observed. While the velocity gradients can be interpreted as infall, rotation or relative motions from sub-cores, the kinematics study shows that the velocity components are best interpreted as convergent flows. We performed a detailed radiative transfer modeling of the velocity structure to one of the sources using the program LIME (Brinch & Hogerheijde 2010), and the result shows consistency with the picture of convergent flows inflowing along the filamentary structure. All together, our study suggests that gravo-turbulent fragmentation occurs at the stagnation of the convergent flows. These cores may be seeds for future massive star formation through competitive accretion. However, as the number of fragments is less than the prediction from the theory, magnetic fields, which have the ability to suppress fragmentation, may play a role in the core-forming process.