A Measurement of the Temperature-Density Relation in the Intergalactic Medium Using a New Lyα Absorption-Line Fitting Method

By P. Mcdonald, J. Miralda-Escudé, M. Rauch, W. Sargent, T. Barlow, Renyue Cen. 2000

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The evolution of the temperature in the intergalactic medium is related to the reionization of hydrogen and helium and has important consequences for our understanding of the Lyα forest and of galaxy formation. We measure the temperature-density relation of intergalactic gas from Lyα forest observations of eight quasar spectra, using a new line fitting technique to obtain a lower cutoff on the distribution of line widths from which the temperature is derived. Using a numerical simulation, we examine the details of this kind of measurement at different densities, finding that the temperature may be difficult to measure for gas with Δg ≲ 1 (Δg is the density of the gas in units of the mean density) because the velocities due to expansion always dominate the widths of the corresponding weak lines, and that the temperature measurement is increasingly ambiguous for gas with Δg ≳ 5 because the dispersion in temperature at fixed density is high. From our observed spectra, the temperature is most precisely determined at densities slightly above the mean: T* = (20,200 ± 2700, 20,200 ± 1300, 22,600 ± 1900) K (statistical error bars) for gas densities Δ* = (1.42 ± 0.08, 1.37 ± 0.11, 1.66 ± 0.11) at redshift z̄ = (3.9, 3.0, 2.4). Systematic errors in T* should be less than 2000 K. The power-law index of the temperature-density relation, defined by T = T*(Δg/Δ*)γ-1, is γ - 1 = (0.43 ± 0.45, 0.29 ± 0.30, 0.52 ± 0.14) for the same three redshifts. The temperature at fixed overdensity Δ = 1.4 is T1.4 = (20,100 ± 2800, 20,300 ± 1400, 20,700 ± 1900) K. This unchanging temperature is higher than expected for photoionized gas in ionization equilibrium with a cosmic background. If the heat from the He II reionization is responsible for the high measured temperature, then the temperature should not be constant but should have a maximum at the end of the reionization epoch. We update the lower limit to the baryon density implied by the observed mean flux decrement.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

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Citations in the corpus

Escape of Ionizing Radiation from High-Redshift Galaxies (2007, background): “…et al. 1999; Bolton et al. 2005), altering the thermal state of the IGM (Gnedin & Hui 1998; Gnedin 2000; Ricotti et al. 2000; Schaye et al. 2000; McDonald et al. 2001; Fechner & Reimers 2007), reducing gas accretion onto small dwarf galaxies (Efstathiou 1992; Thoul & Weinberg 1996; Dijkstra et…”
Primordial Black Holes as Dark Matter: The Power Spectrum and Evaporation of Early Structures (2003, methodology): “4 = 20500 ± 2600 K and γ − 1 = 0.4± 0.2 from McDonald et al. (2001).”
The physics of the intergalactic medium (2007, background): “No significant change in the temperature or polytropic index over the redshift range 2.4 < z < 3.9 is found by McDonald et al. (2001, 2003).”
He ii REIONIZATION AND ITS EFFECT ON THE INTERGALACTIC MEDIUM (2008, methodology): “Although, both McDonald et al. (2001) and Zaldarriaga et al. (2001) measured the temperature in three coarse bins centered at z = 2.4, 3.0 and 3.9, possibly obscuring a sudden temperature change.”
The Lyα Forest Power Spectrum from the Sloan Digital Sky Survey (2004, background): “4 = (20100± 3400, 20300± 2400, 20700± 2800)K and γ − 1 = (0.43 ± 0.45, 0.29 ± 0.3, 0.52 ± 0.14) at z = (3.9, 3.0, 2.4) (see McDonald et al. (2001) – we added 2000 K in quadrature to the temperature errors to allow for systematic errors).”
The Lyman-α forest in three dimensions: measurements of large scale flux correlations from BOSS 1st-year data (2011, background): “, Jeans smoothing, which is determined by the temperature history of the gas [42, 43].”
Toward a Precise Measurement of Matter Clustering: Lyα Forest Data at Redshifts 2-4 (2000, methodology): “The relatively high temperature (in CWPKH we used T0 = 5600K) is motivated by evidence that the high-z IGM is hotter than we previously assumed (Theuns et al. 1999; Bryan & Machacek 2000; Ricotti et al. 2000; Schaye et al. 2000; McDonald et al. 2001).”
The First Cosmic Structures and Their Effects (2004, background): “…(i) the value of the IGM temperature from the Lyα forest at z ≈ 2 − 4 (e.g. Bryan & Machacek 2000; Ricotti, Gnedin & Shull 2000; Schaye et al. 2000b; McDonald et al. 2001; Meiksin, Bryan & Machacek 2001; Zaldarriaga, Hui & Tegmark 2001); (ii) the abundance of neutral hydrogen at z > 6 from the…”
Detection of extended He II reionization in the temperature evolution of the intergalactic medium (2010, methodology): “The first has been to measure the distribution of Doppler parameters of individual absorption features (Schaye et al. 2000; Ricotti et al. 2000; McDonald et al. 2001).”
Toward a Measurement of the Cosmological Geometry at z ~ 2: Predicting Lyα Forest Correlation in Three Dimensions and the Potential of Future Data Sets (2001, methodology): “Of course, the change in PF ðkÞ caused by pressure differences for reasonable changes in the temperature near the measured value (see McDonald et al. 2001) is much smaller than the difference between PM and HPM simulations.”
The Linear Theory Power Spectrum from the Lyα Forest in the Sloan Digital Sky Survey (2004, methodology): “For coding simplicity, we use these measurements as rebinned by McDonald et al. (2001): for z ¼ (2:46; 3:12; 3:58), T1:4 ¼ (16;000 1300; 19;600 1200; 14; 900 1600) K and 1 ¼ (0:34 0:07; 0:06 0:07; 0:22 0:10).”
Lyα Radiation from Collapsing Protogalaxies. I. Characteristics of the Emergent Spectrum (2005, background): “The exact value of he i is a function of redshift and is well known from studies of the Ly forest (e.g., Songaila & Cowie 2002; Lidz et al. 2002; McDonald et al. 2001) and is tabulated in Table 1.”
THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z ∼ 2–3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY (2012, background): “And indeed, observed distributions of thermally broadened absorption lines exhibit higherbd for absorbers with higherNHI (Pettini et al. 1990; Schaye et al. 2000; Bryan & Machacek 2000; Ricotti et al. 2000; McDonald et al. 2001).”
The Evolution of the Intergalactic Medium (2015, background): “…et al. 2012; Rudie, Steidel & Pettini 2012; Bolton et al. 2014; Boera et al. 2014), following-up the seminal investigations from over a decade ago (Schaye et al. 2000; Ricotti, Gnedin & Shull 2000; McDonald et al. 2001; Zaldarriaga, Hui & Tegmark 2001; Theuns et al. 2002a; Hui & Haiman 2003).”
The Lyman alpha forest opacity and the metagalactic hydrogen ionization rate at z~ 2-4 (2004, background): “At present there are only weak observational constraints on the index γ of the temperature density relation and its dependence on redshift (Ricotti et al. 2000; Schaye et al. 2000; McDonald et al. 2001).”
The DESI Experiment Part I: Science,Targeting, and Survey Design (2016, background): “For broadband spectra constraints the bias and damping parameters depend on the amplitude and slope of the linear power spectrum, temperature-density relation [115], and mean level of absorption [116], all of which are varied in our Fisher matrix calculations.”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, methodology): “…= (2.10±0.45)× 104 K at z = 2.4, T0 = (2.3±0.35)×10 4 K at z = 3, and T0 = (2.2 ± 0.2) × 10 4 K at z = 3.9.5 We adopt the Zaldarriaga et al. (2001) values, consistent with those obtained by McDonald et al. (2001) from the same data set but with an independent line-fitting method, in our analysis.”
21-cm fluctuations from inhomogeneous X-ray heating before reionization (2006, background): “At low redshift, observations of the Lyα forest place constraints on the temperature of the IGM after reionization (Schaye et al. 2000; McDonald et al. 2001; Zaldarriaga, Hui & Tegmark 2001; Theuns et al. 2002; Hui & Haiman 2003).”