Extreme Value Statistics of the Halo and Stellar Mass Distributions at High Redshift: are JWST Results in Tension with ΛCDM? (2208.10479v2)

Abstract: The distribution of dark matter halo masses can be accurately predicted in the $\Lambda$CDM cosmology. The presence of a single massive halo or galaxy at a particular redshift, assuming some baryon and stellar fraction for the latter, can therefore be used to test the underlying cosmological model. A number of recent measurements of very large galaxy stellar masses at high redshift ($z > 8$) motivate an investigation into whether any of these objects are in tension with $\Lambda$CDM. We use extreme value statistics to generate confidence regions in the mass-redshift plane for the most extreme mass haloes and galaxies. Tests against numerical models show no tension, neither in their dark matter halo masses nor their galaxy stellar masses. However, we find tentative $> 3\sigma$ tension with recent observational determinations of galaxy masses at high redshift from both HST & JWST, despite using conservative estimates for the stellar fraction ($f_{\star} \sim 1$). Either these galaxies are in tension with $\Lambda$CDM, or there are unaccounted for uncertainties in their stellar mass or redshift estimates.

• The paper applies extreme value statistics on simulation data to predict the most massive halos at high redshift (z > 5).
• It translates halo mass probability distributions into stellar mass estimates using a log-normal model for stellar fractions.
• The study finds tensions between certain JWST high-redshift candidates and ΛCDM predictions, prompting a re-evaluation of observational uncertainties.

An Analysis of High-Redshift Halo and Stellar Mass Distributions using Extreme Value Statistics

The paper "Extreme Value Statistics of the Halo and Stellar Mass Distributions at High Redshift: Are JWST Results in Tension with $\Lambda$CDM?" explores the application of Extreme Value Statistics (EVS) to evaluate whether recent high-redshift galaxy observations align with the predictions of the $\Lambda$CDM cosmological model. The authors, C.C. Lovell et al., address a pertinent question arising from recent data obtained from telescopes such as the James Webb Space Telescope (JWST), which has revealed massive galaxies at high redshifts, potentially challenging the standard cosmological paradigm.

Key Contributions

The authors utilize EVS to predict the mass of the most massive dark matter haloes and stellar masses of galaxies at high redshift ($z > 5$) within a $\Lambda$CDM framework. The method allows for evaluating whether individual extreme galaxies are consistent with theoretical predictions.

1. Halo Mass Distribution: The authors first employ EVS to compute the PDF of the most massive haloes at various fixed redshift hypersurfaces. Using simulations (EAGLE and FLARES), they find agreement between the predicted and the observed most massive halo masses, ensuring EVS robustness on this scale.
2. Transformation to Stellar Masses: The paper goes further to account for baryonic physics by converting halo mass PDFs into stellar mass PDFs, incorporating uncertainties such as stellar fraction distributions. The adoption of a log-normal distribution for the stellar fraction facilitates the translation of uncertainties into predicted stellar masses.
3. Comparison with Observations: EVS predictions are juxtaposed with high-redshift observational data from both pre-JWST studies and the early JWST findings. For instance, substantial tension is noted with some proposed high-redshift galaxies, including certain JWST candidates, potentially casting doubt on their high-mass, high-redshift nature.
4. Implications for Future Surveys: Predictions are proffered for several upcoming large-scale surveys, like those planned with JWST, Euclid, and Roman, providing a benchmark against which future discoveries can be tested for consistency with $\Lambda$CDM predictions.

Implications and Future Directions

The implications of this paper are manifold. Firstly, it highlights that some recent high-mass, high-redshift galaxy observations, if confirmed, might necessitate a re-evaluation of our current cosmological understanding. However, the authors also stress the significant margin for unaccounted errors in observational data, particularly in redshift and stellar mass estimations.

From a methodological standpoint, EVS offers a powerful approach for cosmologists to evaluate the statistical probability of extreme observations. The paper's robustness is underscored by its consistent handling of simulated data, providing confidence in the extension of these statistics to observational datasets.

Looking forward, as the observational capabilities expand with forthcoming surveys, EVS will play a critical role in discerning the alignment of observed cosmological structures against theoretical expectations. Moreover, enhancing the fidelity of observational data, especially regarding redshift determination and mass estimation, remains crucial for interpreting potential tensions with $\Lambda$CDM.

Conclusion

This paper forms a critical reflection on extreme cosmic structures within the framework of current cosmological models. By employing Extreme Value Statistics, the authors offer a nuanced perspective on galaxy formation and evolution, compelling the scientific community to re-assess the fidelity of both observations and theoretical models alike. Continued refinement in both these domains will further illuminate the early epochs of the universe and the theoretical frameworks we use to model them.