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Article overview
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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 | Services: | Forum | Review | PDF | Favorites |
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