Early Fragmentation in Infrared Dark Clouds
Speaker: Kaho Morii
Abstract:
The study of infrared dark clouds (IRDCs) sheds light on the initial conditions governing the formation of high-mass stars and stellar clusters. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, mosaicked by the Atacama Large Millimeter/submillimeter Array. These clumps, characterized by their darkness at 70 μm, as well as their density and low temperature, are thought to be the ideal sites as the birthplace of high-mass stars. We succeeded in identifying an unprecedented number of 839 cores, with masses between 0.05 and 81 Msun. With this large sample, we investigated the fragmentation properties in the very early stage of high-mass star formation. By employing the minimum spanning tree method, we calculated core separations ranging from 0.1 pc to 0.4 pc. To discern the dominant mechanism behind early fragmentation, as well as the hierarchical nature of the process, we compared these observed core separations and masses with those expected from Jeans length and masses, respectively. Our analysis implies that thermal Jeans fragmentation of clumps is the dominant mechanism deriving the observed properties especially for the formation of gravitationally bound cores. Additionally, we find that some clumps exhibit a wide dynamic range of core masses, spanning from low to high masses while others show a narrower range. Clumps with a higher protostellar core fraction tend to display a wider range. Furthermore, our sample highlights the complex nature of fragmentation, characterized by various patterns such as aligned, spread, and concentrated distributions. These findings provide valuable insights into the mechanisms deriving high-mass star formation.