An X-ray Emission Study of the Milky Way Halo’s Clumpy Distribution

Surrounding the Milky Way (MW) is an extended region of hot X-ray emitting gas, generally referred to as the halo or circumgalactic medium (CGM). The CGM has a significant effect on the evolution of the MW. The balance of gas entering and exiting the CGM is unknown, as is the proportion of the gas entering the CGM that is ejected from the MW disk. Light can be shed on these processes by studying the distribution of the soft X-ray emitting hot gas in the CGM. The HaloSat CubeSat has completed an all-sky survey of soft X-ray emission appropriate for this sort of analysis. A previous study based on HaloSat observations has mapped the distribution of emission in the southern (<-30 degrees Galactic latitude) CGM. That study found the emission to be clumpy, a sign that the emission is dominated by gas ejected from the MW disk by feedback processes like OB stars or supernovae. The methods used in that study are now being refined and also applied to the northern CGM (>30 degrees Galactic latitude). The northern CGM is revealed to feature a clumpy distribution similar to the south. An additional hotter component (kT ~ 0.7 keV) of the CGM is strongly detected throughout the majority of the northern and southern CGM.