Circumgalactic Medium in X-ray absorption

We report the first detection of nonthermal broadening of O VII lines in the warm-hot ≈1e6 K circumgalactic medium of the Milky Way (Das S., 2024, ApJL, 963, L48).  In addition to the main goal of studying the target quasars, the same data has been used before to study the density and mass distribution of the warm-hot CGM of our Galaxy and external galaxies, warm-hot intergalactic medium, and super-virial 1e7 K hot phase in the CGM of our Galaxy. Our paper opens up a new dimension to utilize the existing data that has not been explored before.

The temperature of the cool CGM is estimated from the velocity width of OVI absorption lines. Recently, some OVI lines were discovered showing unusually high velocity width. Does this "broad OVI" come from a hotter gas? We test this using 1.2 Ms Chandra data and detect OVII absorption in the same sky direction, and at a similar redshift of the "broad OVI" at >99.9% confidence, making it the first detection of hot CGM in X-ray absorption around an external galaxy. (Mathur, Das, et al. 2023, MNRASL, 525, L11) [Figure: The redshifted OVII absorption in the normalized spectrum] 

Simultaneous (and first) detection and characterization of super-virial (1e7.5 K), virial (1e6.2 K),  and sub-virial (1e5.5 K) phases of the CGM of the Milky Way probed in X-ray absorption: evidence for non-solar chemical composition and non-thermal line broadening (Das et al. 2021, ApJ, 918, 83). The CGM is multi-phase even in X-ray, and way more complex than is usually assumed!