Poster Presentation
Properites of giant molecular clouds in the starburst galaxy NGC 1808
Presenter: Yoshiyuki Yajima (Hokkaido University)
Since stars form in deep and dense parts in giant molecular clouds (GMCs), to reveal properties of them and their dependence on galactic environments are important. Previous studies find the similar scaling relations and properties of GMCs in the Galaxy and galaxies in the local universe including the Local Group. These results suggest that GMCs are rather uniform objects across galaxies. However, GMCs found in more extreme environments such as centers of starburst galaxies deviate from those found in normal star-forming or quiescent galaxies. Accordingly, we investigate GMC properties using the 12CO(J=1-0) data obtained with ALMA for the starburst barred spiral galaxy NGC 1808. We found the fraction of missing flux increases toward the center in the bar. It suggests that GMCs are shredded or converted into small clouds due to strong shear and velocity gradient along the bar. We identify GMCs with a clump finding algorithm and derive their representative properties. Virial parameter of GMCs in the bar is significantly higher than those in arms. Moreover, we can trace the evolutionary sequence of GMCs that it is difficult for them to contribute to star formation as falling along the bar and in the upstream of the central ring, whereas GMCs rapidly glow up, are compressed, and become gravitationally unbound in the downstream of the ring and the nucleus. It is perhaps a cause of starburst in the center of NGC 1808. The dependence of GMC properties on galactic structures is conserved even when ACA data is excluded. Namely, differences of GMC properties among structures are also conserved for GMCs with a high degree of cloud-like structures (excluding diffuse component). The high pressure (surface density) environment in NGC 1808 may be a key to set properties of GMCs.
asiaa.sinica.edu.tw