Multiple temperature components of the hot circumgalactic medium of the Milky Way

TL;DR

This study reveals that the Milky Way's circumgalactic medium contains multiple discrete temperature components, challenging previous models of a single-temperature halo, through detailed X-ray emission and absorption analysis.

Contribution

It provides the first detailed modeling showing multiple temperature components in the Milky Way's circumgalactic medium using combined emission and absorption spectra.

Findings

Identification of two distinct temperature components from emission spectra.

Discrepancy between emission and absorption temperature measurements.

Evidence for 3 to 4 discrete temperature phases in the CGM.

Abstract

We present a deep XMM-Newton observation of the Galactic halo emission in the direction of the blazar 1ES 1553+113. In order to extract the Galactic halo component from the diffuse soft X-ray emission spectrum, accurately modeling the foreground components is crucial. Here we present complex modeling of the foregrounds with unprecedented details. A careful analysis of the spectrum yields two temperature components of the halo gas (T$^{em}_1$= 10$^{6.25-6.42}$K, T$^{em}_2$= 10$^{6.68-6.92}$K). We find that these temperatures obtained from the emission spectrum are not consistent with those from the absorption spectrum (T$^{ab}_1$= 10$^{6.07-6.13}$K, T$^{ab}_2$= 10$^{6.96-7.15}$K), unlike the previous studies that found only one temperature component of the Milky Way circumgalactic medium. This provides us with interesting insights into the nature of emitting and absorbing systems. We discuss several possibilities objectively, and conclude that most likely we are observing multiple (3 to 4) discrete temperatures between 10$^{5.5}$K and $\geqslant$10$^7$K in the Milky Way circumgalactic medium.