Supervirial hot phase in Milky Way circumgalactic medium: further evidences

Abstract

ABSTRACT Recent discoveries of a supervirial hot phase of the Milky Way circumgalactic medium (CGM) have launched new questions regarding the multiphase structure of the CGM around the Galaxy. We use 1.05 Ms of archival Chandra/high-energy transmission grating observations to characterize highly ionized metal absorption at z = 0 along the line of sight of the quasar NGC 3783. We detect two distinct temperature phases with T$_1 = 5.83^{+0.15}_{-0.07}$ K, warm–hot virial temperature, and T$_2=6.61^{+0.12}_{-0.06}$ K, hot supervirial temperature. The supervirial hot phase coexisting with the warm–hot virial phase has been detected in absorption along only two other sightlines and in one stacking analysis. There is scatter in temperature of the hot as well as warm–hot gas. Similar to previous observations, we detect supersolar abundance ratios of metals in the hot phase, with a Ne/O ratio 2σ above solar mixtures. These new detections continue the mystery of the mechanism behind the supervirial hot phase, but provide evidence that this is a true property of the CGM rather than an isolated observation. The supervirial CGM could hold the key to understanding the physical and chemical history of the Milky Way.