http://arxiv.org/abs/2106.13243
For the first time, we present the simultaneous detection and characterization of three distinct phases at $>10^5$ K in $z=0$ absorption, using deep $\it{Chandra}$ observations toward Mrk 421. The extraordinarily high signal-to-noise ratio ($\geqslant60$) of the spectra has allowed us to detect a $\it{hot}$ phase of the Milky Way circumgalactic medium (CGM) at 3.2$^{+1.5}_{-0.5}\times$ 10$^7$ K, coexisting with a $\textit{warm-hot}$ phase at 1.5$\pm$0.1$\times$10$^6$ K and a $\textit{warm}$ phase at 3.0$\pm$0.4$\times$10$^5$ K. The $\textit{warm-hot}$ phase is at the virial temperature of the Galaxy, and the $\textit{warm}$ phase may have cooled from the $\textit{warm-hot}$ phase, but the super-virial $\textit{hot}$ phase remains a mystery. We find that [C/O] in the $\textit{warm}$ and $\textit{warm-hot}$ phases, [Mg/O] in the $\textit{warm-hot}$ phase and [Ne/O] in the $\textit{hot}$ phase are super-solar, and the $\textit{hot}$ and the $\textit{warm-hot}$ phases are $\alpha-$enhanced. Non-thermal line broadening is evident in the $\textit{warm-hot}$ and the $\textit{hot}$ phases and it dominates the total line broadening. Our results indicate that the $>10^5$ K CGM is a complex ecosystem. It provides insights on the thermal and chemical history of the Milky Way CGM, and theories of galaxy evolution.
S. Das, S. Mathur, A. Gupta, et. al.
Mon, 28 Jun 21
7/51
Comments: 18 pages, 2 tables, 5 figures, 2 appendices (with 1 figure), accepted for publication in ApJ (main)