Abstract
Abstract Using Suzaku data, we had found a 3.4σ evidence for the X-ray emitting warm–hot circumgalactic medium (CGM) in the L ⋆ galaxy NGC 3221. Here we present XMM-Newton data and outline an efficient, rigorous, and well-defined method to extract the faint CGM signal. We confirm the CGM detection at 4σ significance within 30–200 kpc of the galaxy. We claim with 99.62% confidence that the CGM is extended beyond 150 kpc. The average temperature of the CGM is K, but it is not isothermal. We find suggestive evidence for a declining temperature gradient out to 125 kpc and for supervirial temperature within 100 kpc. While a supervirial temperature component has been detected in the Milky Way CGM, this is the first time a temperature gradient has been observed in the warm–hot CGM of any spiral galaxy. The emission measure profile is well-fit with either a β-model or a constant-density profile. Deeper data are required to constrain the temperature and density profiles. We also confirm the Suzaku result that the warm–hot CGM is one of the most massive baryon components of NGC 3221 and can account for the missing galactic baryons.
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