A new measurement of the intergalactic temperature at z ∼ 2.55–2.95

Abstract

We present two measurements of the temperature-density relationship (TDR) of the intergalactic medium (IGM) in the redshift range 2.55 < z < 2.95 using a sample of 13 high-quality quasar spectra and high resolution numerical simulations of the IGM. Our approach is based on fitting the neutral hydrogen column density N HI and the Doppler parameter b of the absorption lines in the Lyα forest. The first measurement is obtained using a novel Bayesian scheme which takes into account the statistical correlations between the parameters characterising the lower cut-off of the b − N HI distribution and the power-law parameters T 0 and γ describing the TDR. This approach yields T 0 /10 3 K = 15.6 ± 4.4 and γ = 1.45 ± 0.17 independent of the assumed pressure smoothing of the small scale density field. In order to explore the information contained in the overall b − N HI distribution rather than only the lower cut-off, we obtain a second measurement based on a similar Bayesian analysis of the median Doppler parameter for separate column-density ranges of the absorbers. In this case we obtain T 0 /10 3 K = 14.6 ± 3.7 and γ = 1.37 ± 0.17 in good agreement with the first measurement. Our Bayesian analysis reveals strong anti-correlations between the inferred T 0 and γ for both methods as well as an anti-correlation of the inferred T 0 and the pressure smoothing length for the second method, suggesting that the measurement accuracy can in the latter case be substantially increased if independent constraints on the smoothing are obtained. Our results are in good agreement with other recent measurements of the thermal state of the IGM probing similar (over-)density ranges.

A New Measurement of the Temperature–density Relation of the IGM from Voigt Profile Fitting

“…To test if the source of this discrepancy originates from the way in which the Voigtprofile algorithm was applied to the respective datasets, we plotted the line width distributions for both our line lists for two intervals of 1 dex in N HI within the cut- Figure 22. Comparison of T 0 and γ contours in Rorai et al (2018) and this work (LS method in green, LD method in purple) at z = 2.8. The contours correspond to the 68% and 95% confidence regions.…”

“…We present a detailed comparison of our measurements of p(T 0 , γ) at z = 2.8 with those of Rorai et al (2018) 1.8 Figure 17. Evolution of γ(z) and T 0 (z) compared to models.…”

“…Comparison of normalized log b-distributions of data inRorai et al (2018) in the redshift bin 2.55 ≤ z ≤ 2.95 and this work in the redshift bin 2.7 ≤ z < 2.9.Rorai et al 18 This work LS method(Hiss et al 18) This work LD method(Hiss et al 18) …”

Thermal State of the Intergalactic Medium at z ∼ 2–4

“…The simulations are carried out on a grid of the IGM thermal parameters (T 0 and γ) and extended to the inter-grid values by means of the Gaussian process interpolation of the principal components of the kernel-density smoothed (N, b) maps. This method is similar to various cutoff-fitting methods where the position of the cutoff (or other discrete measures, such as, e.g., a distribution median (Rorai et al 2018)) is calibrated trough the hydrodynamical simulations, however Hiss et al (2019) calibrate the whole lines parameters distribution instead. The main complication with this approach is that the simulations are actually computationally expensive, especially when the line sample size is large, so that the (T 0 , γ) grid resolution need to be small enough to obtain the robust inference of the thermal parameters which is free from the interpolation errors (Hiss et al 2019).…”

Three- and two-point spatial correlations of intergalactic medium at z ∼ 2 using projected quasar triplets

“…Using a group of background quasars, we can probe different physical processes at different scales: (i) The H i density and velocity fields at the scales of few 100 cKpc may have thermal memory of cosmic reionization in the form of pressure broadening (Peeples et al 2010;Rorai et al 2018); (ii) at the scale of ∼ 1 pMpc we can probe matter clustering around massive galaxies (quasar hosts and intervening metal systems) and various feedback processes connecting gas flows between galaxies and the IGM. At present these scales are best probed using quasar pairs (see for example, Prochaska et al 2013); (iii) at the scales of one to few Mpc, one is probing the cosmic structure of filaments and voids and the effect of radiative feed back from bright persistent objects like quasars (e.g Finley et al 2014;Lee et al 2018); and (iv) the Baryon Acoustic Oscillations (BAO) at ∼100 Mpc probes primordial density fluctuations at very large scales (Ata et al 2018).…”