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Date and Time of the Query: 2019-04-25 T19:43:47 PDT
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For refcode 2007ApJ...666..139B:
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2007ApJ...666..139B The Search for Million Degree Gas through the N VII Hyperfine Line Joel N. Bregman and Jimmy A. Irwin Abstract. Gas in the million degree range occurs in a variety of astronomical environments, and it may be the main component of the elusive missing baryons at low redshift. The N VII ion is found in this material and has a hyperfine spin-flip transition with a rest frequency of 53.042 GHz, which can be observed for z>0.1, when it is shifted into a suitably transparent radio band. We used the 42 -- 48 GHz spectrometer on the Green Bank Telescope to search for both emission and absorption from this N VII transmission. For absorption studies, 3C 273, 3C 279, 3C 345, and 4C +39.25 were observed, but no features were seen above the 5 {sigma} level. For emission line studies, we observed Abell 1835, Abell 2390, and the star-forming galaxy PKS 1345+12, but no features were seen exceeding 5 {sigma}. We examine whether the strongest emission feature, in Abell 2390 (3.7 {sigma}), and the strongest absorption feature, toward 4C +39.25 (3.8 {sigma}), might be expected from theoretical models. The emission feature would require ~10^10^ M_sun_ of 10^6^ K gas, which is inconsistent with X-ray limits for the O VII K{alpha} line, so it is unlikely to be real. The N VII absorption feature requires a N VII column of 6x10^16^ cm^-2^, higher than model predictions by at least an order of magnitude, which makes it inconsistent with model expectations. The individual observations were less than 1 hr in length, so for lengthy observations, we show that N VII absorption line observations can begin to be useful in the search for hot intergalactic gas. Key words: Galaxies: Cooling Flows, galaxies: clusters: individual (Abell 1835), Galaxies: Clusters: Individual: Name: Abell 2390, Galaxies: Starburst, Galaxies: Quasars: Absorption Lines, Radio Lines: General
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