Widespread Detection of Two Components in the Hot Circumgalactic Medium of the Milky Way

Abstract

Surrounding the Milky Way (MW) is the circumgalactic medium (CGM), an extended reservoir of hot gas that has significant implications for the evolution of the MW. We used the HaloSat all-sky survey to study the CGM's soft X-ray emission in order to better define its distribution and structure. We extend a previous HaloSat study of the southern CGM (Galactic latitude b < −30 • ) to include the northern CGM (b > 30 • ) and find evidence that at least two hot gas model components at different temperatures are required to produce the observed emission. The cooler component has a typical temperature of kT ∼ 0.18 keV, while the hotter component has a typical temperature of kT ∼ 0.7 keV. The emission measure in both the warm and hot components has a wide range (∼ 0.005 − 0.03, ∼ 0.0005 − 0.004 cm −6 pc respectively), indicating that the CGM is clumpy. A patch of relatively consistent CGM was found in the north, allowing for the CGM spectrum to be studied in finer detail using a stacked spectrum. The stacked spectrum is well described with a model including two hot gas components at temperatures of kT = 0.166 ± 0.005 keV and kT = 0.69 +0.04 −0.05 keV. As an alternative to adding a hot component, a neon-enhanced single-temperature model of the CGM was also tested and found to have worse fit statistics and poor residuals.

The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- I: Halo Gas Properties and the Role of SMBH Feedback

“…Observations of the Milky Way halo report a temperature component around ∼ 10 6.3 K (Bluem et al 2022), which is roughly consistent with the second peak observed in the TNG50 temperature distributions. In addition, observational studies infer gas phases as hot as ∼ 10 6.5 K (southern galactic sky Kaaret et al 2020) and ∼ 10 6.9 K (northern galactic sky Bluem et al 2022) in the Milky Way halo, albeit the abundance of these phases is uncertain.…”

“…Observations of the Milky Way halo report a temperature component around ∼ 10 6.3 K (Bluem et al 2022), which is roughly consistent with the second peak observed in the TNG50 temperature distributions. In addition, observational studies infer gas phases as hot as ∼ 10 6.5 K (southern galactic sky Kaaret et al 2020) and ∼ 10 6.9 K (northern galactic sky Bluem et al 2022) in the Milky Way halo, albeit the abundance of these phases is uncertain. The temperature of gas within the eROSITA bubble(s) (see Introduction) has been inferred to be about 10 6.5 K with Suzaku (Kataoka et al 2013) and 10 6.6−6.7 K from the modelling of OVII and OVIII emission lines (Miller et al 2016).…”

Chandra measurements of gas homogeneity and turbulence at intermediate radii in the Perseus Cluster

“…The abundance Z and the galactic absorption 𝑁 𝐻 were fixed, following Mantz et al (2022). A fit with a third thermal component of ∼ 0.6𝑘𝑒𝑉 was also attempted (Urban et al 2014;Bluem et al 2022, see e.g. ), but this did not result in an improved fit.…”