A GLIMPSE of Abell S1063

Article reproduced from 2025 Transactions of La Société Guernesiaise

A GLIMPSE of Abell S1063

Galaxy clusters are the largest gravitationally bound structures in the Universe, and act as natural magnifying glasses, allowing us to observe distant, faint galaxies which we would otherwise never be able to see. As a consequence of Einstein’s theory of general relativity, the deep gravitational well formed by the collective mass of many galaxies and their associated dark matter haloes magnifies background galaxies through the distortion of space-time. This distortion causes light emitted from galaxies behind the cluster to be magnified and distorted. The amount of magnification depends on the relative location of the background galaxy, but small volumes of space close to the so-called ‘critical curve’, where the magnification diverges towards infinity, can result in magnification factors of several thousand, which is enough to allow us to observe individual stars ( see e.g. Godzilla [2] & Mothra [3]) at z > 2, which lived over 10 billion years ago!

The James Webb Space Telescope (JWST), launched in 2022, has continued the Hubble Space Telescope’s (HST) legacy of observing such lensing clusters. Indeed one of Hubble’s largest dedicated programs for any science goal was the Hubble Frontier Fields, which observed six clusters for a total of 630 hours of integration time, resulting in some of the deepest observations ever taken by HST.

In September 2024, JWST performed its own observations of one of the HFF clusters, Abell S1063, resulting in one of the deepest images taken by JWST during the almost week-long integration. This galaxy cluster, first identified by [1], is a gravitational lensing cluster at redshift z = 0.39. This means the light from the central object you see in Figure 1 has been travelling for around 4.3 billion years to reach us! The cluster dominates the center of the below image, and the majority of the white-coloured galaxies are members of the cluster, which contains thousands of individual galaxies. The diffuse yellow/green light comes from the intracluster medium, which is a superheated plasma of hydrogen and helium that reaches extreme temperatures of hundreds of millions of degrees. The red arcs are the lensed background galaxies themselves, which are actually normal looking galaxies which have been distorted by the gravitational lens. It is common to observe multiple images of the same lensed galaxy on opposite sides of the lens, and the time delay between the different images due to the different path lengths can be used to study cosmology and independently constrain measurements of e.g. the Hubble constant [4].

Figure 1: False-color RGB color image of Abell S1063 using JWST’s NIRCam instrument. Data courtesy of the GLIMPSE team (PI’s Hakim Atek & John Chisholm, proposal ID 3293). RGB created by Thomas Harvey.

The aim of the GLIMPSE survey is to take advantage of the lensing effect to look for galaxies in the extremely early Universe, which would otherwise be too intrinsically faint to detect. So far two studies have been published using these observations. The first claims to have found the first galaxies at z > 15, which if confirmed would break the record of JADES-GS-z14-0 at z = 14.32 [5]. The second has identified a candidate Population III galaxy, which is a theoretical galaxy containing the first generation of stars which formed directly out of primordial gas from the Big Bang, without any enrichment from the products of previous generations of stars [6]. However more evidence is needed to confirm these exciting claims, and there will be many more papers on Abell S1063 in the years to come! Future JWST programs such as SLICE and VENUS [7, 8] will observe over 75 new lensing clusters which will allow us to identify many more rare, highly magnified galaxies and stars, that are incredibly useful for studying both galaxy evolution and the fundamental cosmology of our universe.

References

[1] Abell G. O., Corwin Harold G. J., Olowin R. P., 1989, ApJS, 70, 1
[2] Diego, José María, et al. “Godzilla, a monster lurks in the Sunburst galaxy.” Astronomy & Astrophysics 665 (2022): A134.
[3] Diego, Jose M., et al. “JWST’s PEARLS: Mothra, a new kaiju star at z= 2.091 extremely magnified by MACS0416, and implications for dark matter models.” Astronomy & Astrophysics 679 (2023): A31.
[4] Pierel, J_D_R, et al. “JWST Photometric Time-delay and Magnification Measurements for the Triply Imaged Type Ia “SN H0pe” at z= 1.78.” The Astrophysical Journal 967.1 (2024): 5
[5] Kokorev, Vasily, et al. “A Glimpse at the New Redshift Frontier Through Abell S1063.” arXiv preprint arXiv:2411.13640 (2024)
[6] Fujimoto, Seiji, et al. “GLIMPSE: An ultra-faint $\simeq $10$^{5} $$ M_ {\odot} $ Pop III Galaxy Candidate and First Constraints on the Pop III UV Luminosity Function at $ z\simeq6-7$.” arXiv preprint arXiv:2501.11678 (2025)
[7] Cerny, Catherine, et al. “Strong LensIng and Cluster Evolution (SLICE) with JWST: Early Results, Lens Models, and High-Redshift Detections.” arXiv preprint arXiv:2503.17498 (2025)
[8] https://www.stsci.edu/jwst/science-execution/program-information?id=6882