A Warm Hot Intergalactic Medium towards 3c 120?

We observed the Seyfert I active galaxy/broad line radio galaxy 3C 120 with the Chandra high energy transmission gratings and present an analysis of the soft X-ray spectrum. We identify the strongest absorption feature (detected at > 99.9% confidence) with O VIII Lyα (FWHM = 1010+295 −265 km s −1), blueshifted by −5500± 140 km s−1 from systemic velocity. The absorption may be due to missing baryons in warm/hot intergalactic medium (WHIGM) along the line-of-sight to 3C 120 at z = 0.0147±0.0005, or it could be intrinsic to the jet of 3C 120. Assuming metallicites of ∼ 0.1Z⊙ , we estimate an ionic column density of NO viii > 3.4×1016cm−2 for WHIGM and a filament depth of < 19h−1 70 Mpc. We find a baryon overdensity > 56 relative to the critical density of a Λ-dominated cold dark matter universe, which is in reasonable agreement with WHIGM simulations. We detect, at marginal significance, absorption of O VIII Lyα at z ∼ 0 due to a hot medium in the Local Group. We also detect an unidentified absorption feature at ∼ 0.71 keV. Absorption features which might be expected along with O VIII Lyα, were not significant statistically. Relative abundances of metals in the WHIGM and local absorbers may therefore be considerably different from solar. Subject headings: galaxies: active – galaxies: individual (3C 120 ) – galaxies: Seyfert – techniques: spectroscopic – X-rays: galaxies – X-rays: galaxies