2019ApJ...885..108D

We report a 3.4σ detection of the warm-hot, massive, extended circumgalactic medium (CGM) around an L^* star-forming spiral galaxy NGC 3221, using deep Suzaku observations. The temperature of the gas is 10^6.1 K, comparable to that of the Milky Way CGM. The spatial extent of the gas is at least 150 kpc. For a β-model of density profile with solar abundance, the central emission measure is EM = (3 ± 1) x 10^–5 cm^–6 kpc and the central electron density is n_eo = (4 ± 1) x 10^–4 cm^–3, with a slope of β = 0.56. We investigate a range of β values and find that the details of the density profile do not change our results significantly. The mass of the warm-hot gas, assuming a metallicity of 1/3 Z_☉, is (16 ± 3) x 10¹⁰ M_☉, which is the most massive baryon component of NGC 3221. The baryon fraction is f_b = 0.120 ± 0.036 (statistical)_–0.048^+0.104 (systematic), consistent with the cosmological mean value, closing the baryon budget of this galaxy. We also investigated the missing metals problem in conjunction with the missing baryons problem and conclude that metals are likely to be preferentially expelled from the galaxy. Ours is the first detection of an extended warm-hot CGM around an external L^* star-forming spiral galaxy, where the CGM likely accounts for the missing galactic baryons.