High-resolution ALMA observations and TIGRESS simulation as probes of the multiphase ISM evolution

Choi, Woorak ; Bureau, Martin ; Liu, Lijie ; Kim, Chang-Goo ; Chung, Aeree

In this study, we present the ISM properties on a GMC scale based on both high-resolution ALMA observations and MHD simulation. We first investigate the GMCs of two barred spiral galaxies (NGC~5806 and NGC~613) using the ALMA CO data with a ~20~pc resolution. We identify GMCs within the 1~kpc centers of the targets, and characterize their properties. We find that the GMCs in the nuclear ring and its vicinity of both galaxies are similar in size to those in the Milky Way disk, but have larger masses, linewidths, and surface densities. GMCs in both systems also have a much steeper size — linewidth relation than in the MW disk or in other galaxies. We suggest that the large linewidths and unusually steep size — linewidth relation are primarily due to gas inflowing toward the center through the bar. In addition, the feedback of star formation, SN, and AGN or cloud-cloud collisions is found to play some roles. These results suggest that the substructures of galaxies such as a bar and a nuclear ring can strongly influence the physical properties and evolution of GMCs. We also utilize the TIGRESS simulations of 4 pc-resolution to probe the impact of environments on multiphase ISM. In particular, we investigate how the external pressure of other medium such as ram pressure due to the ICM affects the ISM. Our simulations reveal that the workings of ram pressure stripping are not only direct acceleration of the ISM but also mixing-driven momentum transfer involving phase transition and radiative cooling. The hot ICM passes through the low-density channels of the porous, multiphase ISM and shreds the cool ISM, creating mixing layers. The ICM momentum is transferred through those mixing layers while populating the intermediate-temperature gas and radiating thermal energy away. The mixing-driven momentum transfer predicts that the more ICM mixes in, the faster the ISM moves, resulting in the anticorrelation of outflow velocity and gas metallicity of the stripped ISM. The compression of the ISM disks due to the ICM ram pressure enhances star formation rates up to 50% compared to the model without ICM. With the ICM ram pressure higher than the disk anchoring pressure, star formation is quenched within ~100 Myr.

https://ui.adsabs.harvard.edu/abs/2024AAS...24344801C/abstract