Observational research of fragmentation process in nearby star-forming regions

speaker: Kousuke Ishihara

In the star formation process, molecular clouds hierarchically form dense structures by collapsing and fragmentation, then eventually leading to protostars. The scale at which fragmentation occurs is considered to contribute to the formation of stellar systems such as clusters and multiples. The most basic case is thermal Jeans fragmentation, which is determined by the balance between self-gravity and the pressure gradient due to thermal motion, and the expected characteristic fragmentation scale is called thermal Jeans length. Comparing with the core separation distribution and Jeans length provides a clue to the fragmentation process from clumps to cores. We have analyzed ALMA data (spatial resolution: ∼ 1000 au at 3 kpc) for 30 high-mass star-forming regions. As a result, we found a characteristic peak at ∼ 6000 au, which is comparable to the Jeans length. We have also confirmed that the result is robust even if considering observational biases due to differences in spatial resolution and mass sensitivity. In this talk, I introduce preliminary results of a similar analysis applied to dense cores in nearby star-forming regions. I obtained separation distribution by applying a Minimum Spanning Tree to the core coordinates in core catalogs obtained from the Herschel Gould Belt Survey. The results show a variety of distribution shapes with peaks at >10000 au in each region. The peak separation was found to be about 0.1 times the Jeans length in all regions. This may indicate that dynamical processes such as cloud-scale gravitational instability are important in the core formation process.