[Paper Review] Do high redshift QSOs and GRBs corroborate JWST?

Eoin Ó Colgáin, M. M. Sheikh-Jabbari+1 more|arXiv (Cornell University)|May 30, 2024

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper investigates whether high-redshift quasars (QSOs) and gamma-ray bursts (GRBs) corroborate the anomalous massive high-redshift galaxies observed by the James Webb Space Telescope (JWST). Using frequentist profile likelihoods and Bayesian MCMC methods, it finds significant tensions—7.9σ for QSOs and 3.9σ for GRBs—between these data sets and the Planck-ΛCDM model, indicating that both QSO and GRB data prefer higher matter density Ωₘ at high redshifts, consistent with JWST's findings and challenging the standard cosmological model.

ABSTRACT

The James Webb Space Telescope (JWST) is reporting massive high redshift galaxies that appear challenging from the $Λ$CDM perspective. Interpreted as a cosmological problem, this necessitates the Planck collaboration underestimating either matter density $Ω_m$ or physical matter density $Ω_m h^2$ at higher redshifts. Through standard frequentist profile likelihoods, we identify corroborating quasar (QSO) and gamma-ray burst (GRB) data sets where $Ω_m$ increases with effective redshift $z_{ extrm{eff}}$ and remains anomalously large at higher redshifts. We relax the traditional priors by allowing for $Ω_m > 1$, consistent with negative dark energy density, to locate profile likelihood peaks where possible. While the variation of $Ω_m$ with $z_{ extrm{eff}}$ is at odds with the $Λ$CDM model, demarcating frequentist confidence intervals through differences in $χ^2$ in profile likelihoods, the prevailing technique in the literature, points to $3.9 σ$ and $7.9 σ$ tensions between GRBs and QSOs, respectively, and Planck-$Λ$CDM. We explain the approximations inherent in the existing profile likelihood literature, and highlight fresh methodology that generalises the prescription. We show that alternative methods, including Bayesian approaches, lead to similar tensions. Finally, in the large sample limit, we show that Feldman-Cousins prescription for frequentist confidence intervals in the presence of a boundary (prior) leads to confidence intervals that are bounded above by Wilks' theorem.

Motivation & Objective

• To assess whether independent high-redshift data sets (QSOs and GRBs) corroborate the anomalous massive high-redshift galaxies observed by JWST.
• To test whether the observed tension in Ωₘ values from JWST can be independently confirmed using QSO and GRB data.
• To evaluate the robustness of frequentist profile likelihoods in quantifying statistical tension and propose generalized methods.
• To compare results from frequentist and Bayesian approaches (e.g., MCMC) in assessing the significance of deviations from Planck-ΛCDM.

Proposed method

• The authors use standard frequentist profile likelihoods to compute differences in χ² between Planck-ΛCDM and high-redshift QSO/GRB data sets to quantify statistical tension.
• They apply the profile likelihood method to 220 GRBs from a published data set and 136 QSOs from the Risaliti-Lusso sample, fitting them to the flat ΛCDM model.
• The analysis fixes H₀ = 70 km/s/Mpc to break degeneracy in the parameter space and extract Ωₘ posterior distributions.
• They validate results using MCMC sampling with emcee and GetDist, confirming the tension through posterior distributions and histogram analysis of Ωₘ values.
• The study compares frequentist χ² differences with Bayesian MCMC-based p-values to assess the robustness of the tension estimates.
• They highlight limitations in existing profile likelihood methods and propose a generalized framework for more accurate uncertainty quantification.

Experimental results

Research questions

• RQ1 Do high-redshift QSOs and GRBs show consistent deviations in matter density Ωₘ from the Planck-ΛCDM model, similar to those inferred from JWST observations?
• RQ2 What is the statistical significance of the tension between high-redshift QSO/GRB data and Planck-ΛCDM when quantified via profile likelihoods and MCMC?
• RQ3 How do frequentist and Bayesian methods compare in assessing the tension, and do they yield consistent conclusions?
• RQ4 To what extent do the observed trends in Ωₘ with effective redshift z_eff challenge the ΛCDM paradigm?
• RQ5 Can the observed anomalies in QSOs and GRBs be interpreted as independent corroborations of the JWST-observed high-redshift galaxy mass anomalies?

Key findings

• The QSO data set shows a 7.9σ tension with Planck-ΛCDM, indicating a significantly higher matter density Ωₘ at high redshifts.
• The GRB data set exhibits a 3.9σ tension with Planck-ΛCDM, with the posterior distribution of Ωₘ peaking at ∼5 and showing no values below the Planck 1σ upper bound.
• MCMC analysis confirms the tension, with no sampled Ωₘ values falling within the Planck 1σ interval (Ωₘ ≤ 0.322), yielding a conservative p < 1/31933.
• The probability of obtaining a Ωₘ value consistent with Planck within 1σ is less than 0.003%, indicating a very low chance of compatibility.
• Both QSO and GRB data sets prefer anomalously high Ωₘ values at high redshifts, consistent with the higher Ωₘ and Ωₘh² values inferred from JWST observations.
• The study demonstrates that alternative methods, including Bayesian MCMC, yield similar tensions, reinforcing the robustness of the result.