Optimal 1D Ly α forest power spectrum estimation – II. KODIAQ, SQUAD, and XQ-100

Abstract

We measure the 1D Ly α power spectrum P1Dfrom Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ), The Spectral Quasar Absorption Database (SQUAD) and XQ-100 quasars using the optimal quadratic estimator. We combine KODIAQ and SQUAD at the spectrum level, but perform a separate XQ-100 estimation to control its large resolution corrections in check. Our final analysis measures P1Dat scales k < 0.1 s km−1between redshifts z = 2.0–4.6 using 538 quasars. This sample provides the largest number of high-resolution, high-S/N observations; and combined with the power of optimal estimator it provides exceptional precision at small scales. These small-scale modes (k ≳ 0.02 s km−1), unavailable in Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) analyses, are sensitive to the thermal state and reionization history of the intergalactic medium, as well as the nature of dark matter. As an example, a simple Fisher forecast analysis estimates that our results can improve small-scale cut off sensitivity by more than a factor of 2.

Possible evidence for a large-scale enhancement in the Lyman-$α$ forest power spectrum at redshift $\mathbf{\textit{z}\geq 4}$

“…We now apply our updated analysis framework to the observational measurements of the 1D Ly𝛼 forest power spectrum at 4 ≤ 𝑧 ≤ 4.6 presented recently by Karaçaylı et al (2022). The Karaçaylı et al (2022) 2017)).…”

“…We now apply our updated analysis framework to the observational measurements of the 1D Ly𝛼 forest power spectrum at 4 ≤ 𝑧 ≤ 4.6 presented recently by Karaçaylı et al (2022). The Karaçaylı et al (2022) 2017)). The flux power spectrum measurements are made in a total of 15 redshift bins, in the range of 𝑧 = 1.8−4.6 with bin size Δ𝑧 = 0.2.…”

“…Canonically, the ionization state of the IGM is determined by the UV photons emitted by stars and active galactic nuclei. As a result, intergalactic Ly𝛼 absorption is also a key probe of the final stages of the reionization era at 𝑧 > 5 (Fan et al 2006;Becker et al 2015;Eilers et al 2018;Bosman et al 2022) A widely used statistic for characterising the Ly𝛼 forest is the 1D power spectrum of the transmitted flux (McDonald et al 2000;Palanque-Delabrouille et al 2013;Iršič et al 2017b;Walther et al 2018;Boera et al 2019;Karaçaylı et al 2022). When studying the IGM approaching the reionization era, the 1D power spectrum is useful in several different ways.…”

“…In this work we will build on M22 by investigating the possibility of detecting inhomogeneous reionization using the 1D Ly𝛼 forest power spectrum on large scales. For this purpose we will make use of the recent 1D power spectrum measurements presented by Karaçaylı et al (2022) using data from the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) (O'Meara et al 2017), the Spectral Quasar Absorption Database (SQUAD) (Murphy et al 2019) and the XQ-100 survey (López et al 2016). Importantly, these data extend to larger scales, log 10 (𝑘/km −1 s) −3, compared to Boera et al (2019), although the precision is still rather modest, with relative uncertainties in the power spectrum of 10-20 per cent.…”

“…In Section 3 we consider the effect of patchy reionization on the Ly𝛼 power spectrum, and introduce a new parameterisation that allows the power spectrum template presented by M22 to be implemented within our Markov Chain Monte Carlo analysis in a more general, model independent way. In Section 4, we apply our framework to the data presented by Karaçaylı et al (2022) and discuss the possible evidence for an enhancement in power on large scales. We furthermore consider the possibility of applying our analysis to future, higher precision data before concluding in Section 5.…”