Constraints on the Pop III Sky Surface Brightness from High-Redshift Caustic Transients in MACS0416
Abstract
Population III (Pop III) stars are hypothetical zero-metallicity stellar structures formed from primordial hydrogen and helium. They are theorized to span a wide mass range, extending to several 100 solar masses, and may have played important roles in nucleosynthesis and reionization. Their expected fluxes are far below JWST NIRCam detection limits, making direct observation unlikely. However, extreme magnification near the caustics of massive foreground galaxy clusters may enable their detection. We search for overlooked high-redshift (7 <= z <= 17) caustic transits in the lensing cluster MACS J0416.1-2403. Using three observations spanning 126 days, we create difference images to identify potential candidates. Critical curves for sources at 7 <= z <= 17, derived from a strong-lensing model, guided visual inspection of three difference-images. No additional transits were found. The longer caustics in our model sweep a larger source-plane area, increasing the probability of detecting an event. Combining this increased statistical sensitivity with deeper imaging, we establish a fainter limit for the unresolved stellar population at z >= 7. From this null result, we constrain the 100 solar mass 2 micron Pop III sky surface brightness to >= 32.8 +/- 0.6 mag arcsec^-2. Modeling the non-detection as a Poisson process gives a posterior mean caustic-transit rate of 0.29 cluster^-1 yr^-1 and a 95 percent upper credible limit of lambda_95 = 0.86 cluster^-1 yr^-1. The inferred rate remains consistent with the adopted fiducial Pop III caustic-transit model and provides an empirical benchmark for future multi-epoch monitoring campaigns. This search exploits the fact that individual stars projected close to source-plane caustics can be briefly magnified far beyond their unlensed fluxes. These constraints provide a direct test of the abundance of luminous Pop III stars at early cosmic times.
Related
- DETECT: Real-Time Identification of Transients with DESI Spectroscopic Redshift
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- The connection between surface brightness and satellite systems for central galaxies through IllustrisTNG (Corrigendum)
- CHEX-MATE: X-ray surface brightness discontinuities across a representative cluster sample
- Euclid: Calibrating distances from surface brightness fluctuations with Early Release Observations of the Fornax cluster
BibTeX
@misc{perivolotis2026constraints,
title = {{Constraints on the Pop III Sky Surface Brightness from High-Redshift Caustic Transients in MACS0416}},
author = {Jakob P. Perivolotis and Pietro Bergamini and Rogier A. Windhorst and Erik Zackrisson and Timothy Carleton and Seth H. Cohen and Jordan C. J. D'Silva and Rachel Honor and Rolf A. Jansen and Anton M. Koekemoer and Rafael Ortiz III and Jake Summers and Dan Coe and Christopher J. Conselice and Jose M. Diego and Brenda Frye and Massimo Ricotti and Gibson B. Bowling and Brent Smith and Christopher N. A. Willmer and Haojing Yan},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19757},
eprint = {2609.19757},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19757},
note = {CC0},
}
RIS
TY - UNPB
TI - Constraints on the Pop III Sky Surface Brightness from High-Redshift Caustic Transients in MACS0416
AU - Jakob P. Perivolotis
AU - Pietro Bergamini
AU - Rogier A. Windhorst
AU - Erik Zackrisson
AU - Timothy Carleton
AU - Seth H. Cohen
AU - Jordan C. J. D'Silva
AU - Rachel Honor
AU - Rolf A. Jansen
AU - Anton M. Koekemoer
AU - Rafael Ortiz III
AU - Jake Summers
AU - Dan Coe
AU - Christopher J. Conselice
AU - Jose M. Diego
AU - Brenda Frye
AU - Massimo Ricotti
AU - Gibson B. Bowling
AU - Brent Smith
AU - Christopher N. A. Willmer
AU - Haojing Yan
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.19757
UR - https://arxiv.org/abs/2609.19757
AB - Population III (Pop III) stars are hypothetical zero-metallicity stellar structures formed from primordial hydrogen and helium. They are theorized to span a wide mass range, extending to several 100 solar masses, and may have played important roles in nucleosynthesis and reionization. Their expected fluxes are far below JWST NIRCam detection limits, making direct observation unlikely. However, extreme magnification near the caustics of massive foreground galaxy clusters may enable their detection. We search for overlooked high-redshift (7 <= z <= 17) caustic transits in the lensing cluster MACS J0416.1-2403. Using three observations spanning 126 days, we create difference images to identify potential candidates. Critical curves for sources at 7 <= z <= 17, derived from a strong-lensing model, guided visual inspection of three difference-images. No additional transits were found. The longer caustics in our model sweep a larger source-plane area, increasing the probability of detecting an event. Combining this increased statistical sensitivity with deeper imaging, we establish a fainter limit for the unresolved stellar population at z >= 7. From this null result, we constrain the 100 solar mass 2 micron Pop III sky surface brightness to >= 32.8 +/- 0.6 mag arcsec^-2. Modeling the non-detection as a Poisson process gives a posterior mean caustic-transit rate of 0.29 cluster^-1 yr^-1 and a 95 percent upper credible limit of lambda_95 = 0.86 cluster^-1 yr^-1. The inferred rate remains consistent with the adopted fiducial Pop III caustic-transit model and provides an empirical benchmark for future multi-epoch monitoring campaigns. This search exploits the fact that individual stars projected close to source-plane caustics can be briefly magnified far beyond their unlensed fluxes. These constraints provide a direct test of the abundance of luminous Pop III stars at early cosmic times.
ER -