Discovery of a Hot, Multiphase Ne VIII/O VI Absorber in the Low-Redshift IGM

Details Discovery of a Hot, Multiphase Ne VIII/O VI Absorber in the Low-Redshift IGM Discovery of a Hot, Multiphase Ne VIII/O VI Absorber in the Low-Redshift IGM

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aspc..348..363s&link_type=abstract

Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE ASP Conference Series, Vol. 348, Proceedings of the Confe

Astronomy and Astrophysics

Astrophysics

1

Scientific paper

High resolution FUSE and STIS observations of the bright QSO HE 0226--4110 (zem = 0.495) reveal the presence of a multi-phase absorption line system at zabs(O VI) = 0.20701 containing absorption from H I (Ly α to Ly θ), C III, O III, O IV, O VI, N III, Ne VIII, Si III, and S VI. This represents the first detection of intergalactic Ne VIII, a diagnostic of gas with T ˜ 7× 105 K. Single component fits to the Ne VIII and O VI absorption yield log N(Ne VIII) = 13.89± 0.11, v = -7± 6 km s-1 and log N(O VI) = 14.37± 0.03, v = 0± 2 km s-1. Through the entire absorber, N(Ne VIII)/N(O VI) = 0.33± 0.10. The O VI and Ne VIII are not likely created in a low density medium photoionized solely by the extragalactic background at z = 0.2; the required path length for [Z/H] = -0.5 of ˜11 Mpc implies the Hubble flow absorption line broadening would be ˜10 times greater than the observed line widths. With [Ne/H] and [O/H] = -0.5, the value N(Ne VIII)/N(O VI) = 0.33± 0.10 is consistent with gas in collisional ionization equilibrium near T=5.4× 105 K with log N(H)= 19.9 and N(H)/N(H I) = 1.7 × 106. The observations of O VI and Ne VIII in the z = 0.20701 system support the basic idea that a substantial fraction of the baryonic matter at low redshift exists in hot very highly ionized gaseous structures. Absorption by the moderately ionized gas (including O IV and S VI) is well modeled by gas in photoionization equilibrium with [Z/H] = -0.5± 0.2, T = 2.1× 104 K, nH= 2.6× 10-5 cm-3, P/k ˜ 0.5 cm-3 K, and path length of ˜60 kpc. These values suggest the moderately ionized absorber may be associated with the modestly enriched photoionized gas in a galaxy group or the outermost regions of a galaxy halo.

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