Spectral shape of the UV ionizing background and HeII absorption at redshifts 1.8 < z < 2.9

Abstract

The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE2347-4342, Q1157+3143, and HS1700+6416 in the redshift interval 1.8 < z < 2.9. The systems are analyzed by means of the Monte Carlo Inversion method completed with the spectral shape recovering procedure. The UVB spectral shape fluctuates at 2.4 < z < 2.9 mostly due to radiative transfer processes in the clumpy IGM. At z < 1.8, the IGM becomes almost transparent both in the HI and HeII Lyman continua and the variability of the spectral shape comes from diversity of spectral indices describing the QSO/AGN intrinsic radiation. At z > 2.4, the recovered spectral shapes show intensity depression between 3 and 4 Ryd due to HeII Ly-alpha absorption in the IGM clouds (line blanketing) and continuous medium (true Gunn-Petersen effect). The mean HeII Ly-alpha opacity estimated from the depth of this depression corresponds within 1-2sigma to the values directly measured from the HI/HeII Ly-alpha forest towards the quasars studied. The observed scatter in eta = N(HeII)/N(HI) and anti-correlation between N(HI) and eta can be explained by the combined action of variable spectral softness and differences in the mean gas density between the absorbing clouds. Neither of the recovered spectral shapes show features which can be attributed to the putative input of radiation from soft sources like starburst galaxies.

20 pages, 20 figures. Accepted for publication in A&A

References in corpus (4)

• The UV spectrum of HS1700+6416 II. FUSE observations of the HeII Lyman alpha forest
• The most metal-poor damped Ly alpha system at z<3: constraints on early nucleosynthesis
• Fluctuations of the intergalactic UV background towards two lines of sight
• The UV spectrum of HS1700+6416 I. Predicting the metal line content of the far UV spectrum

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• The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra
• The History and Morphology of Helium Reionization
• Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies
• The evolution of the helium-ionizing background at z ~ 2-3
• Fluctuations in the Ionizing Background During and After Helium Reionization
• The nature of NV absorbers at high redshift
• Probing Large-scale UV Background Inhomogeneity Associated with Quasars using Metal Absorption