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28 March 2024
 
  » arxiv » arxiv.0706.1214

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A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers
Todd M. Tripp ; Kenneth R. Sembach ; David V. Bowen ; Blair D. Savage ; Edward B. Jenkins ; Nicolas Lehner ; Philipp Richter ;
Date 8 Jun 2007
Abstract(Abridged) Using high-resolution ultraviolet spectra of 16 low-z QSOs, we study the physical conditions and statistics of O VI absorption systems in the intergalactic medium (IGM) at z < 0.5. We identify 53 intervening [z(abs) < z(QSO)] O VI systems comprised of 78 individual components, and we find 14 associated systems [within 5000 km/s of z(QSO)] containing 34 components. For intervening systems [components] with rest-frame equivalent width W(r) > 30 mA, the number of O VI absorbers per unit redshift dN/dz = 18.3(+3.0/-2.6) [24.8(+3.5/-3.1)], and this decreases to dN/dz = 0.9(+1.0/-0.5) [0.3(+0.7/-0.3)] for W(r) > 300 mA. The number per redshift increases steeply as z(abs) approaches z(QSO), and some associated systems have substantially lower H I/O VI ratios. Many of the intervening absorbers have similar O VI and H I profiles, which suggests a single-phase origin. Moreover, these well-aligned single-phase absorbers are relatively cold. Based on the O VI and H I b-values, we find that 37% of the intervening components have T < 10^{5} K, i.e., cooler than than expected in the "warm-hot" IGM. We show that the cool O VI absorbers are inconsistent with available equilibrium and non-equilibrium collisional ionization models but are easily understood if photoionized. However, we find that 47% of the intervening O VI systems are more complex multiphase absorbers, and we show that these complex absorbers can accomodate warm-hot gas with T > 10^{5} K and lower metallicity.
Source arXiv, arxiv.0706.1214
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