Cosmological observational tests in the JWST Era. I: angular size - redshift

TL;DR

This study leverages the ASTRODEEP-JWST galaxy catalog to test the angular size–redshift relation under two cosmologies: the standard expanding ΛCDM model and a static tired-light model. By deriving angular and linear sizes for thousands of galaxies (spec-z and photo-z) and employing a fixed standard ruler (D = 10 kpc), the authors quantify galaxy-size evolution via D ∝ (1+z)^{α}. They find a pronounced size evolution in ΛCDM with α ≈ −1, consistent with cosmic expansion, whereas the tired-light model shows little to no evolution, highlighting a tension with a static universe picture. Volume-limited subsamples and multiple statistical approaches reinforce the ΛCDM trend and reduce selection biases, underscoring the utility of JWST data for cosmological tests and the need for cosmology-independent size estimators in galaxy evolution studies.

Abstract

This study is devoted to the cosmological "angular size - redshift" test. An analysis is performed of the angular and linear sizes of galaxies from the new ASTRODEEP-JWST catalogue, which contains over 500,000 objects at high redshifts (up to ~20 photometrically determined and up to ~14 spectroscopically determined). For the calculations, 6 860 galaxies with reliably determined spectroscopic redshifts and 319,771 galaxies with known photometric redshifts were used. The linear sizes of galaxies were computed within the framework of two cosmological models - the standard (ΛCDM) model and one of the static models (the so-called "tired light" model). We have shown that within the framework of the ΛCDM model, a significant evolution of the linear sizes of galaxies is observed, with the rate of the evolution closely matching the rate of the cosmic expansion. In contrast, in the static model, the characteristic linear sizes of galaxies exhibit almost no evolution with increasing z.

Figures (6)

• Figure 1: Angular size as a function of redshift. Observational data (galaxies) are shown as points: black for spectroscopic $z$, grey for photometric $z$. Theoretical curves for a linear size of $D = 10$ kpc are shown as solid lines for the $\Lambda$CDM model (red), the "tired light" model (blue), and the linear Hubble law (green). Angular sizes of galaxies were taken as twice the catalogue value of the effective radius.
• Figure 2: Linear sizes (effective diameters) of galaxies as a function of redshift. Top panel: only galaxies with the spectroscopic redshifts; bottom panel: galaxies with the photometric $z$. Red points correspond to calculations based on the $\Lambda$CDM model; blue points to those based on the "tired light" model.
• Figure 3: Evolution of the linear sizes (effective diameters) of galaxies within the $\Lambda$CDM model. Data points represent individual galaxies; the curves show best-fit regression lines for subsamples with different minimum redshifts. Shaded regions indicate the $3\sigma$ uncertainty of the fit. Top panel: spectroscopic redshifts; bottom panel: photometric redshifts.
• Figure 4: Evolution of galaxy linear sizes (effective diameters) in the $\Lambda$CDM model, statistics for 50 redshift bins. Points show the mean galaxy sizes in each bin with their standard errors of the mean (grey points denote bins excluded due to low redshift or insufficient number of objects). Lines indicate the best-fit curves; shaded areas show the $3\sigma$ formal fitting uncertainty. Top: spectroscopic redshifts, bottom: photometric redshifts.
• Figure 5: $z$ vs. $M_{UV}$ diagram and volume-limited samples in the $\Lambda$CDM model. Top panel: spectroscopic redshifts; bottom panel: photometric redshifts. Volume-limited samples are shown in colour.