The warm-hot, extended, massive circumgalactic medium of NGC 3221: an XMM-Newton discovery
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 2.0+0.2-0.3 × 106 K, but it is not isothermal. We find suggestive evidence for a declining temperature gradient out to 125 kpc and for super-virial temperature within 100 kpc. While a super-virial 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.