A refined measurement of the mean transmitted flux in the Lyα forest over 2 < z < 5 using composite quasar spectra

By George D. Becker, Paul Hewett, G. Worseck, J. X. P. KICCIoA, Cambridge, U. Observatory, University of California Santa Cruz. 2012

137 citations recorded by the source corpus.

We present new measurements of the mean transmitted flux in the Lyα forest over 2 < z < 5 made using 6065 quasar spectra from the Sloan Digital Sky Survey data release 7 (SDSS DR7). We exploit the general lack of evolution in the mean quasar continuum to avoid the bias introduced by continuum fitting over the Lyα forest at high redshifts, which has been the primary systematic uncertainty in previous measurements of the mean Lyα transmission. The individual spectra are first combined into 26 composites with mean redshifts spanning 2.25 ≤ zcomp ≤ 5.08. The flux ratios of separate composites at the same rest wavelength are then used, without continuum fitting, to infer the mean transmitted flux, F(z), as a fraction of its value at z ∼ 2. Absolute values for F(z) are found by scaling our relative values to measurements made from high-resolution data by Faucher-Gigu` ere et al. at z ≤ 2.5, where continuum uncertainties are minimal. We find thatF(z) evolves smoothly with redshift, with no evidence of a previously reported feature at z � 3.2. This trend is consistent with a gradual evolution of the ionization and thermal state of the intergalactic medium over 2 < z < 5. Our results generally agree with the most careful measurements to date made from high-resolution data, but offer much greater precision and extend to higher redshifts. This work also improves upon previous efforts using SDSS spectra by significantly reducing the level of systematic errors.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b6c8edfde4a39fd2316a259e15a2c7f72b501823

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Citations in the corpus

New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization (2013, methodology): “The effective optical depths from Becker et al. (2013) consist of twenty-eight ταeff values over 2.15 6 zα 6 4.85 in bins of ∆zα = 0.1, while the temperature measurements consist of eight T (∆̄) measurements over 2.0 < zT < 4.8 in bins of ∆zT = 0.4.”
The Giant Gemini GMOS survey of zem > 4.4 quasars – I. Measuring the mean free path across cosmic time (2014, background): “For our fiducial models, we set δαT = 0 and γ τ = 2.5, where the latter is motivated by observed redshift evolution in the Lyman series effective optical depth of the IGM (Becker et al. 2013; Prochaska et al. 2014).”
Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six (2014, methodology): “The Lyβ and Lyα spectra were drawn randomly, with the optical depths in the foreground Lyα sample collectively scaled to reproduce the mean Lyα opacity at zfg measured by Becker et al. (2013).”
The Neutral Hydrogen Cosmological Mass Density at z = 5 (2015, methodology): “The number of clumps was set such that the mean transmission in the Lyα forest matches the effective optical depth at z = 4.5 derived by Becker et al. (2013).”
DISCOVERY OF THREE z > 6.5 QUASARS IN THE VISTA KILO-DEGREE INFRARED GALAXY (VIKING) SURVEY (2013, methodology): “The only difference between the procedure of Willott et al. (2005) and our procedure is that we have updated the transmission–redshift relation to reflect new measurements recently published by Becker et al. (2013) for redshifts up to z 5.”