Mg X is a good tracer for the hot gaseous halo of isolated galaxies, tracing gas around one million Kelvin. Against continuum of the background QSO LBQS 1435-0134, we discovered the first Mg X candiate (5.8 sigma) associated with the galaxy halo. The Ne VIII at the same velocities increases the confidence for this detection (Qu & Bregman 2016).
By stacking 12 nearby spiral galaxies, we detected the extended hot gas halo (log M~10.9) around L* galaxies (>4 sigma) (Bregman et al. 2020). This detection indicates that the hot halo around L* galaxies can extend to at least 180 kpc, about twice of the previous boundary determined by X-ray imaging.
We develop a semi-analytic gaseous halo model connecting the galaxy disk and the gaseous halo by assuming that the star formation rate on the disk is balanced by the radiative cooling rate of the gaseous halo, including stellar feedback. This model enable us to study gaseous halos in a larger parameter space than simulations (Qu & Bregman 2018a).
Adopting our gaseous halo model, we calculate the gaseous halo contribution to the observed column density distributions for hot ions by convolving the gaseous halo model with the stellar mass function. This plot is our prediction for the 2-D distribution of O VI and Ne VIII, showing a positive correlation between these two ions (Qu & Bregman 2018b).
The MW disk and CGM is traced by absorptions (e. g., Si IV) against stellar or AGN continuum. However, there is a significant disagreement between the stellar sample and the AGN sample ( Zheng19; SW09). This tension is alleviated by Qu & Bregman (2019) by introducing a 2-D model accounting for the radial profile of the disk component.
The column density line shape encodes both the gas spatial distribution and the velocity field. Qu et al. (2020a) developed a kinematical model to extract the gas distribution and velocity. There is a north-south asymmetry -- the north sky has a net infall (red lines), while the yellow lines do not have radial velocity. Also, the north sky has more gases.
Qu et al. (2020b) reported the discovery of a hot bridge (log T ~ 6.3) connecting the MW with M31, which is detected in both X-ray (O VII and O VIII emission lines) and SZ. The plateau shape is explained by a cylinder with a length of 420 kpc and a radius of 120 kpc. This bridge accounts for logM ~ 11-11.7 of the total baryonic mass.