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Surprises from the hot circumgalactic medium (CGM) of the Milky Way (MW) and MW-like nearby star-forming galaxies

Presentation #107.05 in the session “ISM/Galaxies/Clusters (Poster)”.

Published onApr 01, 2022
Surprises from the hot circumgalactic medium (CGM) of the Milky Way (MW) and MW-like nearby star-forming galaxies

Observations of the hot circumgalactic medium (CGM) have taken a great stride in the last two decades thanks to the advent of X-ray facilities like Chandra, XMM-Newton, and Suzaku. With the upcoming missions in the current and the next decade, this field is going to take a giant leap and become one of the centers of scientific attraction in Galactic/extragalactic astronomy. In that context, I will talk about my dissertation on the hot CGM of the Milky Way and a nearby L* galaxy, NGC 3221.

By probing the hot CGM of the Milky Way using absorption lines of multiple metals (e.g., C, N, Ne, Mg, Si, and Fe) in addition to oxygen, we have discovered a 107 K phase coexisting with the well-known 106 K and 105.5K gas phases, with non-solar chemical composition and non-thermal line broadening. The emission analyses toward the same direction as the absorption analyses have revealed that the emitting and the absorbing gas are not probing the same temperature components, clearly ruling out the simplified picture of the single-temperature hot CGM. For a galaxy like the Milky Way, these are super exciting results, because theories of galaxy evolution have not sufficiently explored this parameter space.

The observations of the nearby L* spirals complement our observation of the Milky Way. By carefully choosing the right instrument, optimum target, and following a rigorous method, we have extracted the faint emission from the diffuse, extended (>150 kpc), massive hot CGM of NGC 3221, which can account for the missing galactic baryons of NGC 3221. There is evidence of super-virial temperature and a temperature gradient within 100 kpc of NGC 3221, suggesting an imprint of galactic feedback. This is the first external L* galaxy with such exciting findings.

These results provide insight into the impact of stellar feedback on the hot CGM. Also, these will set a benchmark for designing experiments with upcoming X-ray telescopes.

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