Strong z~0.5 O VI Absorption Toward PKS 0405-123: Implications for Ionization and Metallicity of the Cosmic Web - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: We present observations of the O VI system at z abs = 0.495096 toward PKS0405-123 z em = 0.5726 obtained with FUSE and STIS. In addition to strong OVI, with log NO VI = 14.47+-0.02, and moderate H I this absorber shows CIII, N IV, O IV, and O V, with upper limits for another seven ions. The largenumber of available ions allows us to test ionization models usually adoptedwith far less contraints. We find the ionic column densities cannot be matchedby collisional ionization models, in or out of equilibrium. Photoionizationmodels can match the observed column densities, including O VI. If one assumesphotoionization by a UV background dominated by QSOs, the metallicity of thegas is O-H = -0.15, while a model for the UV background with contributionsfrom ionizing photons escaping from galaxies gives O-H = -0.62. Both giveN-O ~ -0.6 and C-H ~ -0.2 to -0.1. The choice of ionizing spectrum ispoorly constrained. Multiphase models with a contribution from bothphotoionized gas at T~10^4 K and collisionally ionized gas at T~1-3x10^5K can also match the observations giving very similar metallicities. The O VIin this system is not necessarily a reliable tracer of WHIM matter. We do notdetect Ne VIII or Mg X absorption. The limit on Ne VIII-O VI < 0.21 3 sigma,the lowest yet observed. Thus this absorber shows no firm evidence of the-warm-hot intergalactic medium- at T~0.5-3x10^6 K thought to contain asignificant fraction of the baryons at low redshift. We present limits on thetotal column of warm-hot gas in this absorber as a function of temperature.This system would be unlikely to provide detectable X-ray absorption in theions O VII or O VIII even if it resided in front of the brighter X-ray sourcesin the sky.



Autor: J.Christopher Howk, Joseph S. Ribaudo, Nicolas Lehner Univ. of Notre Dame, J. Xavier Prochaska UC Santa Cruz, Hsiao-Wen Chen Univ

Fuente: https://arxiv.org/







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