Fluctuations of the intergalactic ionization field at redshiftz~ 2

Abstract

Aims. To probe the spectral energy distribution (SED) of the ionizing background radiation at z 2 and to specify the sources contributing to the intergalactic radiation field. Methods. The spectrum of a bright quasar HS 1103+6416 (z em = 2.19) contains five successive metal-line absorption systems at z abs = 1.1923, 1.7193, 1.8873, 1.8916, and 1.9410. The systems are optically thin and reveal multiple lines of different metal ions with the ionization potentials lying in the extreme ultraviolet (EUV) range (∼1 Ryd to ∼0.2 keV). For each system, the EUV SED of the underlying ionization field is reconstructed by means of a special technique developed for solving the inverse problem in spectroscopy.For the z abs = 1.8916 system, the analysis also involves the He i resonance lines of the Lyman series and the He i λ504 Å continuum, which are seen for the first time in any cosmic object except the Sun. Results. From one system to another, the SED of the ionizing continuum changes significantly, indicating that the intergalactic ionization field at z 2 fluctuates at the scale of at least Δ z ∼ 0.004. This is consistent with Δ z 0.01 estimated from He ii and H i Lyman-α forest measurements between the redshifts 2 and 3. A radiation intensity break by approximately an order of magnitude at E = 4 Ryd in SEDs restored for the z abs = 1.1923, 1.8873, 1.8916, and 1.9410 systems points to quasars as the main sources of the ionizing radiation. The SED variability is mostly caused by a small number of objects contributing at any given redshift to the ionizing background; at scales Δ z 0.05, the influence of local radiation sources becomes significant. A remarkable SED restored for the z abs = 1.7193 system, with a sharp break shifted to E ∼ 3.5 Ryd and a subsequent intensity decrease by ∼1.5 dex, indicates a source with comparable inputs of both hard (active galactic nuclei, AGN) and soft (stellar) radiation components. Such a continuum can be emitted by (ultra) luminous infrared galaxies, many of which reveal both a strong AGN activity and intense star formation in the circumnuclear regions.

The UVES large program for testing fundamental physics – II. Constraints on a change in μ towards quasar HE 0027−1836★

“…The shortcomings of the ThAr wavelength calibration of quasar spectra taken with VLT/UVES have already been discussed by a number of authors (Chand et al 2006;Levshakov et al 2006;Molaro et al 2008;Thompson et al 2009a;Whitmore et al 2010;Agafonova et al 2011;Wendt & Molaro 2011;Rahmani et al 2012;Agafonova et al 2013). The availability of 19 independent spectra taken over a 3 year period allows us to investigate the presence of any velocity drift as a function of wavelength in our spectra and study its evolution with time before we embark on ∆µ/µ measurements.…”

HUBBLE SPACE TELESCOPE/COSMIC ORIGINS SPECTROGRAPH OBSERVATIONS OF THE QUASAR Q0302–003: PROBING THE He II REIONIZATION EPOCH AND QSO PROXIMITY EFFECTS

“…(We discuss this possible bias in detail in Appendix A.) Recently, significant η variations have been seen in the post-reionization epoch by looking at metal-line systems (Agafonova et al 2013). This debate aside, there is no question that large η fluctuations are expected prior to the completion of helium reionization, due to the patchy nature of the process and the rarity of the bright quasars responsible (e.g., Fardal et al 1998;Furlanetto 2009;Compostella et al 2013).…”

Microwave and submillimeter molecular transitions and their dependence on fundamental constants

“…At α/α ∼ 10 −5 , the required position accuracy should [12,[42][43][44]. At this level of the systematic errors an estimate of α/α from any individual absorption-line system must be considered as an upper limit but not a 'signal'.…”

“…Such a critical relationship between the 'signal' (expected velocity offset ∆v) and the error σ v hampers measuring ∆α/α at the level of ∼ 10 −5 from any absorption system taking into account all imperfections of the spectrograph and the data reduction procedure. Systematic errors exceeding 0.5 km s −1 are known to be typical for the wavelength calibration in both the VLT/UVES and Keck/HIRES spectrographs [12,[42][43][44]. At this level of the systematic errors an estimate of ∆α/α from any individual absorption-line system must be considered as an upper limit but not a 'signal'.…”