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The hot and the cold circumgalactic medium (CGM) of nearby MW-like galaxies and the Milky Way: a brief review of our recent accomplishments

Presentation #313.03 in the session “Gas in Galaxies”.

Published onJan 11, 2021
The hot and the cold circumgalactic medium (CGM) of nearby MW-like galaxies and the Milky Way: a brief review of our recent accomplishments

We study the thermal structure and the chemical composition of the hot CGM of the Milky Way using X-ray emission and absorption spectroscopy. Probing the hot CGM of the Milky Way using absorption lines of multiple metals (e.g., N, Ne and Fe) in addition to the strongest probes, i.e., OVII and OVIII transitions, we have discovered a 107 K gas coexisting with the well-known ~106 K gas, with alpha-enhancement and non-solar abundance ratios. The emission analysis toward the same direction as the absorption analysis has revealed that the emitting and the absorbing gas are not probing the same temperature components, clearly ruling out the simplified picture of the hot CGM at a single temperature. The observation of the nearby MW-like spirals complement our observation of the Milky Way. By carefully choosing the right instrument, optimum target and following a rigorous method, we have been able to extract the faint emission from the diffuse, extended (>150 kpc), massive (~1011 Msun) hot CGM of a MW-like galaxy, NGC 3221. The hot CGM can account for the missing galactic baryons of NGC 3221. There is also a suggestive evidence of super-virial temperature, and a temperature gradient within 125 kpc. This is the first external spiral galaxy with such exciting findings. We also look for neutral, diffuse CGM around nearby MW-like spirals by comparing the 21-cm emission from single-dishes vs. interferometers. By designing an approach complementary to the existing mapping techniques, we have detected the diffuse, extended (~100 kpc), massive (~108 Msun), quasi-static (vavg~ vsys) neutral CGM around NGC 891 and NGC 4565. Our observational results provide us insight into the impact of stellar feedback, mixing, depletion and hydrodynamics in the CGM, and the possible relation between accretion and star-formation. These results are useful information for upcoming X-ray and radio observations of the CGM.


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