COINCIDENCES BETWEEN O VI AND O VII LINES: INSIGHTS FROM HIGH-RESOLUTION SIMULATIONS OF THE WARM-HOT INTERGALACTIC MEDIUM

摘要

With high-resolution (0.46 h –1?kpc), large-scale, adaptive mesh-refinement Eulerian cosmological hydrodynamic simulations we compute properties of O VI and O VII absorbers from the warm-hot intergalactic medium (WHIM) at z = 0. Our new simulations are in broad agreement with previous simulations with ~40% of the intergalactic medium being in the WHIM. Our simulations are in agreement with observed properties of O VI absorbers with respect to the line incidence rate and Doppler-width-column-density relation. It is found that the amount of gas in the WHIM below and above 106?K is roughly equal. Strong O VI absorbers are found to be predominantly collisionally ionized. It is found that (61%, 57%, 39%) of O VI absorbers of log N(O VI) cm2 = (12.5-13, 13-14, 14) have T 105?K. Cross correlations between galaxies and strong [N(O VI) 1014?cm–2] O VI absorbers on ~100-300?kpc scales are suggested as a potential differentiator between collisional ionization and photoionization models. Quantitative prediction is made for the presence of broad and shallow O VI lines that are largely missed by current observations but will be detectable by Cosmic Origins Spectrograph observations. The reported 3σ upper limit on the mean column density of coincidental O VII lines at the location of detected O VI lines by Yao et?al. is above our predicted value by a factor of 2.5-4. The claimed observational detection of O VII lines by Nicastro et?al., if true, is 2σ above what our simulations predict.