A Direct Precision Measurement of the Intergalactic Lyα Opacity at 2 ≤ z ≤ 4.2

By C. Faucher-Giguére, J. Xavier Prochaska, A. Lidz, L. Hernquist, M. Zaldarriaga. 2007

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We measure the evolution of the intergalactic Lyα effective optical depth, τeff, over the redshift range 2 ⩽ z⩽ 4.2 from a sample of 86 high-resolution, high-S/N quasar spectra obtained with the ESI and HIRES spectrographs on Keck and with the MIKE spectrograph on Magellan. This represents an improvement over previous analyses of the Lyα forest from high-resolution spectra in this redshift interval of a factor of 2 in the size of the data set alone. We pay particular attention to robust error estimation and extensively test for systematic effects. We find that our estimates of the quasar continuum levels in the Lyα forest obtained by spline fitting are systematically biased low, with the magnitude of the bias increasing with redshift, but that this bias can be accounted for using mock spectra. The mean fractional error ⟨ Δ C/Ctrue⟩ is <1% at z = 2, 4% at z = 3, and 12% at z = 4. Previous measurements of τeff at z≳ 3 based on directly fitting the quasar continua in the Lyα forest, which have generally neglected this effect, are therefore likely biased low. We provide estimates of the level of absorption arising from metals in the Lyα forest based on both direct and statistical metal removal results in the literature, finding that this contribution is ≈6%-9% at z = 3 and decreases monotonically with redshift. The high precision of our measurement, attaining 3% in redshift bins of width Δ z = 0.2 around z = 3, indicates significant departures from the best-fit power-law redshift evolution [τeff = 0.0018(1 + z)3.92, when metals are left in], particularly near z = 3.2. The observed downward departure is statistically consistent with a similar feature detected in a precision statistical measurement using SDSS spectra by Bernardi and coworkers using an independent approach.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/35ddb11ab70275cea7afc50a07a029ba76e7b1bd

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Citations in the corpus

The Evolution of the Intergalactic Medium (2015, methodology): “The consensus model is that galaxies drove the reionization of intergalactic hydrogen (e.g. Shapiro, Giroux & Babul 1994; Madau, Haardt & Rees 1999; Faucher-Giguère et al. 2008b; Becker & Bolton 2013).”
GeV gamma-ray attenuation and the high-redshift UV background (2009, methodology): “The high-peaked model, which has a star-formation rate that increases until redshift 5, does produce a somewhat flatter ionization rate, as suggested by Faucher-Giguère et al. (2008).”
The physics of the intergalactic medium (2007, background): “Using a sample of 86 high-resolution high signal-to-noise ratio spectra, however, Faucher-Giguère et al. (2008b) find a feature similar to that reported by Bernardi et al. (2003).”
Probing Galactic Halos with Fast Radio Bursts (2019, background): “Indeed, researchers now invert the experiment to leverage Lyα forest observation and cosmological simulation to assess the EUVB and other cosmological parameters (e.g. Faucher-Giguère et al. 2008b; Palanque-Delabrouille et al. 2013).”
New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization (2013, methodology): “This is primarily because the Songaila & Cowie (2010) values are calculated using an expression that assumes z0 ≃ z (their equation (7); see also Madau et al. (1999), Faucher-Giguère et al. (2008a) equation (22)).”
Lyman-alpha constraints on warm and on warm-plus-cold dark matter models (2008, background): “Part of the physics entering into the Ly-�analysis is not fully understood (for a recent review see [52]), and can be significantly influenced by DM particles (see e.g. [53, 54, 55, 56, 57, 58 ]).”
He ii REIONIZATION AND ITS EFFECT ON THE INTERGALACTIC MEDIUM (2008, methodology): “Bolton et al. (2005), Becker et al. (2007), and especially Faucher-Giguère et al. (2008b) measured the hydrogen photoionization rate (ΓHI) to be flat as a function of redshift using the flux decrement method on 2 < z < 4 HI Lyα forest data and to within a factor of ∼ 2 given by ΓHI(z) = 10 −12 s−1.”
A DEFINITIVE SURVEY FOR LYMAN LIMIT SYSTEMS AT z ∼ 3.5 WITH THE SLOAN DIGITAL SKY SURVEY (2009, methodology): “…constrained cosmological parameters such as the primordial power spectrum and the baryonic mass density and astrophysical parameters like the amplitude of the ionizing background (e.g. Rauch 1998; Croft et al. 2002; McDonald et al. 2005; Tytler et al. 2004; Faucher-Giguère et al. 2008b).”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, methodology): “The main observational constraint we use is our measurement of the Lyα forest effective optical depth between z = 2 and z = 4.2 (Faucher-Giguère et al. 2008c).”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, background): “At z = 3, for example, the diffuse IGM transmits only ≈ 67% of photons immediately blueward of Lyα and this fraction decreases rapidly with increasing redshift (e.g., Faucher-Giguère et al. 2008d).”
A strong redshift dependence of the broad absorption line quasar fraction (2010, methodology): “The implementation employed here incorporates a refined parametrization of the Ly-α forest opacity based on the work of Faucher-Giguère et al. (2008).”
Lyα blobs as an observational signature of cold accretion streams into galaxies (2009, background): “…the flux of photons that was emitted blueward of the Lyα resonance (e.g Fig 3 of Madau 1995), At z = 2, z = 3 and z = 4, the mean transmitted fraction of photons emitted blueward of the Lyα resonance is 〈Tα〉 ∼ 0.8, 〈Tα〉 ∼ 0.7, and 〈Tα〉 ∼ 0.4, respectively (e.g. Faucher-Giguère et al. 2008b).”
A refined measurement of the mean transmitted flux in the Lyα forest over 2 < z < 5 using composite quasar spectra (2012, methodology): “Indeed, Faucher-Giguère et al. (2008) emphasized that the significance of their feature may have been exaggerated by the assumption of an underlying power law evolution in τeff .”
RADIATIVE TRANSFER IN A CLUMPY UNIVERSE. IV. NEW SYNTHESIS MODELS OF THE COSMIC UV/X-RAY BACKGROUND (2011, background): “This trend is consistent with the conclusions reached by Bolton & Haehnelt (2007) and Faucher-Giguère et al. (2008a) from empirical measurements of the Lyα forest opacity.”
Concordance models of reionization: implications for faint galaxies and escape fraction evolution (2012, methodology): “Models of the ionizing background at intermediate redshifts indicate that star-forming galaxies dominate at z & 3 (Haehnelt et al. 2001; Bolton et al. 2005; Faucher-Giguère et al. 2008a, 2009).”
A model for cosmological simulations of galaxy formation physics: multi-epoch validation (2013, methodology): “…luminosity functions, the model was calibrated to satisfy the measured mean transmission of the Ly-alpha forest at intermediate redshifts z = 2−4.2 (Faucher-Giguère et al. 2008a,b), published HeII to HI column density ratios, HeII reionisation by z ∼ 3 (McQuinn et al. 2009), and complete HI…”
Detection of extended He II reionization in the temperature evolution of the intergalactic medium (2010, methodology): “We also plot τeff from Faucher-Giguère et al. (2008), which agrees well with our measurements, particularly at z < 3, where our method is most sensitive to the mean flux (see Section 5.2).”
Extended Lyman-alpha emission from cold accretion streams (2011, methodology): “We adopt in this paper a value of fα = 0.66 based on the work of Faucher-Giguère et al. (2008).”