Systematic Bias in Ionizing Radiation Escape Fraction Measurements from Foreground Large-scale Structures
Abstract We investigate the relationship between the Ly α forest transmission in the intergalactic medium (IGM) and the environmental density of galaxies, focusing on its implications for the measurement of ionizing radiation escape fractions. Using a sample of 268 spectroscopically confirmed background galaxies at 2.7 < z < 3.0 and a galaxy density map at z ≈ 2.5 within the COSMOS field, we measure the Ly α transmission photometrically, leveraging the multiwavelength data available from the COSMOS2020 catalog. Our results reveal a weak but statistically significant positive correlation between Ly α optical depth and galaxy density contrast, suggesting that overdense regions are enriched in neutral gas, which could bias escape fraction measurements. This emphasizes the need to account for the large-scale structure of the IGM in analyses of ionizing radiation escape fractions and highlights the advantages of a photometric approach for increasing the number of sampled lines of sight across large fields. The photometric redshifts provided by upcoming all-sky surveys, such as Euclid, will make it possible to account for this bias, which can also be minimized by using fields separated in the sky by many degrees.
Authors
- Matthew Hayes (ORCID: https://orcid.org/0000-0001-8587-218X)
- Ali Ahmad Khostovan (ORCID: https://orcid.org/0000-0002-0101-336X)
- Marc Rafelski (ORCID: https://orcid.org/0000-0002-9946-4731)
- Sina Taamoli (ORCID: https://orcid.org/0000-0003-0749-4667)
- Yu-Heng Lin (ORCID: https://orcid.org/0000-0001-8792-3091)
- M. Salvato (ORCID: https://orcid.org/0000-0001-7116-9303)
- Caitlin M. Casey (ORCID: https://orcid.org/0000-0002-0930-6466)
- Weida Hu (ORCID: https://orcid.org/0000-0003-3424-3230)
- Claudia Scarlata (ORCID: https://orcid.org/0000-0002-9136-8876)
- Jeyhan S. Kartaltepe (ORCID: https://orcid.org/0000-0001-9187-3605)
- Andreas L. Faisst (ORCID: https://orcid.org/0000-0002-9382-9832)
Institutions
- University of California, Riverside (US)
- California Institute of Technology (US)
- Space Telescope Science Institute (US)
- University of Minnesota (US)
- University of Kentucky (US)
- Johns Hopkins University (US)
- University of California, Santa Barbara (US)
- Rochester Institute of Technology (US)
- Stockholm University (SE)
- Max Planck Institute for Extraterrestrial Physics (DE)
- Université Bourgogne Franche-Comté (FR)
- AlbaNova (SE)
- Infrared Processing and Analysis Center (US)
- The University of Texas at Austin (US)
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2025-05-19
- DOI
- https://doi.org/10.3847/1538-4357/adcf9a
- Citations
- 2
- Primary Topic
- Radiation Detection and Scintillator Technologies
- Type
- article
- Field-Weighted Citation Impact
- 3.77