The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations

Abstract

We present XMM-Newton observations around the sight line of Mrk 421. The emission spectrum of the Milky Way (MW) circumgalactic medium (CGM) shows that a two-phase model is a better fit to the data compared to a single-phase model; in addition to the warm-hot virial phase at log (T/K) = 6.30 ± 0.02, a hot super-virial phase at log (T/K) = 6.88 − 0.06 + 0.07 is required. Furthermore, we present observations of five fields within 5 degrees of the primary field. Their spectra also require a two-phase model at warm-hot and hot temperatures. The hot phase, which was first discovered in Das et al. in 2019, appears to be widespread. By chemical tagging, we show that the emission from the supevirial phase comes from the L-shell transitions of Fe xviii–Fe xxii, and that the range of temperatures probed in emission is distinct from that in absorption. We detect scatter in temperature and emission measure in both the phases, and deduce that there is small-scale density inhomogeneity in the MW CGM. The emitting gas likely has higher density, possibly from regions close to the disk of the MW, while the absorption in the virial phase may arise from low-density gas extended out to the virial radius of the MW. The presence of the super-virial phase far from the regions around the Galactic center implicates physical processes unrelated to the activity at the Galactic center. Hot outflows resulting from star formation activity throughout the Galactic disk are likely to be responsible for producing this phase.

The XMM-Newton Line Emission Analysis Program (X-LEAP). II. The Multiscale Temperature Structures in the Milky Way Hot Gas

“…More recently, the hotter gas surrounding the FBs has been found to form larger X-ray bubbles, the eROSITA bubbles (Predehl et al 2020, Sarkar 2024. Besides the spatial variation of the temperature, a supervirial hot phase with a temperature of ≈5-10 × 10 6 K has been reported by recent studies (e.g., Das et al 2019aDas et al , 2019bGupta et al 2021;Bluem et al 2022;Bhattacharyya et al 2023;Ponti et al 2023). This extremely hot phase is supported by the enhanced emission feature at » -T log K 6.7 7.0 or absorption features of highly ionized species (e.g., Ne IX and Ne X; Das et al 2019a).…”

Mapping the Imprints of Stellar and Active Galactic Nucleus Feedback in the Circumgalactic Medium with X-Ray Microcalorimeters

“…Following these detections, the CGM of other disk galaxies was also explored, albeit to a much lesser extent, due to the lower signal-to-noise ratios (S/ Ns) of these galaxies (e.g., Anderson & Bregman 2011;Anderson et al 2012;Dai et al 2012;Bogdán et al 2013bBogdán et al , 2015Li et al 2017). Despite these successes, however, it is important to realize that all these detections explored massive galaxies (a few ×10 11 M e in stellar mass), while X-ray observations could not detect the CGM emission around MWtype galaxies, with the exception of our own Galaxy (Das et al 2019a(Das et al , 2019b(Das et al , 2021Bhattacharyya et al 2023).…”

Gas Morphology of Milky Way–like Galaxies in the TNG50 Simulation: Signals of Twisting and Stretching

“…The boundary between the warm and hot gas is defined with respect to the virial temperature (many collaborations define the temperature of the hot gas to be equal to, or some fraction of, the virial temperature). For example, see Appleby et al (2021), who define hot gas to have temperatures above 0.5T vir , and Bhattacharyya et al (2023), who define their hot gas to be at the virial temperature (∼10 6 K). Hereafter, we refer to the virial temperature as T vir , which is adapted from Li et al (2017) and is defined below:…”