Absorption signatures of warm-hot gas at low redshift: NeVIII

Abstract

At z<1 a large fraction of the baryons is thought to reside in diffuse gas that has been shock-heated to high temperatures (log T=5-6). Absorption by the 770.41, 780.32 Å doublet of NeVIII in quasar spectra represents a unique tool to study this elusive warm-hot phase. We have developed an analytic model for the properties of NeVIII absorbers that allows for an inhomogeneous metal distribution. Our model agrees with the predictions of a simulation from the OWLS project indicating that the average line-of-sight metal-filling fraction within the absorbing gas is low (c_L~0.1). Most of the NeVIII in our model is produced in low-density, collisionally ionized gas (log n=-6 to -4 cm^-3, log T=5-6). Strong NeVIII absorbers (log N(NeVIII)>14), like those recently detected by HST/COS, are found to arise in higher density gas (log n>-4, log T=5.75). NeVIII cloudlets harbour only 1 per cent of the cosmic baryon budget. The baryon content of the surrounding gas (which has similar densities and temperatures as the NeVIII cloudlets) is a factor 1/c_L higher. We conclude that NeVIII absorbers are robust probes of shock-heated diffuse gas, but that spectra with signal-to-noise ratios S/N>100 would be required to detect the bulk of the baryons in warm-hot gas.

19 pages, 10 figures; MNRAS in press; minor changes with respect to v1

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Cited by in corpus (17)

• The Properties of Low Redshift Intergalactic O VI Absorbers Determined from High S/N Observations of 14 QSOs with the Cosmic Origins Spectrograph
• The COS Absorption Survey of Baryon Harbors (CASBaH): Warm-hot Circumgalactic Gas Reservoirs Traced by Ne VIII Absorption
• AGN proximity zone fossils and the delayed recombination of metal lines
• The abundance and physical properties of O VII and O VIII X-ray absorption systems in the EAGLE simulations
• HST/COS detection of a Ne VIII absorber towards PG 1407+265: An unambiguous tracer of collisionally ionized hot gas?
• An HST/COS legacy survey of intervening SiIII absorption in the extended gaseous halos of low-redshift galaxies
• A Pair of O VI and Broad Ly-alpha Absorbers Probing Warm Gas in a Galaxy Group Environment at z ~ 0.4
• Probing Feedback via IGM tomography and Ly$\alpha$ forest with Subaru PFS, TMT/ELT, and JWST
• Implications of an updated ultraviolet background for the ionization mechanisms of intervening Ne VIII absorbers
• The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray line emission
• Detection of Two Intervening Ne VIII Absorbers Probing Warm Gas at z~0.6
• On the connection between the metal-enriched intergalactic medium and galaxies: an OVI-galaxy cross-correlation study at $z<1$
• A hot gaseous galaxy halo candidate with Mg X absorption
• Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the NeVIII Population
• Role of ionizing background on the statistics of metal absorbers in hydrodynamical simulations
• Role of ionizing background on the non-thermal broadening inferred for the aligned absorbers
• Ultraviolet Perspectives on Diffuse Gas in the Largest Cosmic Structures