Discovery of the hottest component of the Milky Way circumgalactic medium with non-solar abundance ratios
Abstract
I will present our discovery of a very hot (T ~107 K) circumgalactic medium (CGM) of the Milky Way using a deep XMM-Newton observation. It is arguably the hottest component found in the halo of any L* galaxy so far. Interestingly, this gas, coexisting with the warm-hot (T ~106 K) CGM, has a non-solar mixture of Nitrogen, Neon and Oxygen. The multiphase CGM, a huge reservoir of baryons and metals is potentially a key solution to the "missing baryons" and "missing metals" problems. It plays an instrumental role in the evolution of a galaxy by interfacing the pristine inflows and the metal-enriched outflows. However, studying the highly ionized warm-hot CGM has always been challenging because of its faint diffuse signals. Due to the paucity of strong (significantly detectable) metal lines in soft X-ray, Oxygen is used as the primary tracer element. The temperature is calculated using the relative abundance of OVIII and OVII, and the total baryonic and metallic masses are calculated assuming a solar chemical composition. Our results show that I) it is important to include other metals to correctly infer the temperature of the CGM, and II) the assumption of a solar chemistry may affect previous mass estimations of the >106 K CGM from the observations of Oxygen emission and absorption. This would provide insights on the heating and chemical enrichment of the Milky Way CGM, and provide important inputs to theoretical models of galaxy formation and evolution.
- Publication:
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AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1710801D