Using Lyα Absorption to Measure the Intensity and Variability of z ∼ 2.4 Ultraviolet Background Light

Weiss, Laurel H.; Gebhardt, Karl; Davis, Dustin; Mentuch Cooper, Erin; Lujan Niemeyer, Maja; Qezlou, Mahdi; Mirza Khanlari, Mahan; Ciardullo, Robin; Farrow, Daniel; Gawiser, Eric; Gazagnes, Simon; Gronwall, Caryl; Hill, Gary J.; Schneider, Donald P.

Abstract

We present measurements of z ∼ 2.4 ultraviolet (UV) background light using Lyα absorption from galaxies at z ∼ 2–3 in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) database. Thanks to the wide area of this survey, we also measure the variability of this light across the sky. The data suggest an asymmetric geometry where integrated UV light from background galaxies is absorbed by H i within the halo of a foreground galaxy, in a configuration similar to damped Lyα systems. Using stacking analyses of over 400,000 HETDEX LAE spectra, we argue that this background absorption is detectable in our data. We also argue that the absorption signal becomes negative due to HETDEX's sky-subtraction procedure. The amount that the absorption is oversubtracted is representative of the z ∼ 2.4 UV contribution to the overall extragalactic background light (EBL) at Lyα. Using this method, we determine an average intensity (in νJν units) of 12.9 ± 3.7 nW m−2 sr−1 at a median observed wavelength of 4134 Å, or a rest-frame UV background intensity of 508 ± 145 nW m−2 sr−1 at z ∼ 2.4. We find that this flux varies significantly depending on the density of galaxies in the field of observation. Our estimates are consistent with direct measurements of the overall EBL.

Citation

Weiss, L. H., Gebhardt, K., Davis, D., Mentuch Cooper, E., Lujan Niemeyer, M., Qezlou, M., Mirza Khanlari, M., Ciardullo, R., Farrow, D., Gawiser, E., Gazagnes, S., Gronwall, C., Hill, G. J., & Schneider, D. P. (2025). Using Lyα Absorption to Measure the Intensity and Variability of z ∼ 2.4 Ultraviolet Background Light. The Astrophysical journal, 983(1), Article 72. https://doi.org/10.3847/1538-4357/adc0f9

• Journal Article Type: Article
• Acceptance Date: Mar 13, 2025
• Online Publication Date: Apr 8, 2025
• Publication Date: Apr 10, 2025
• Deposit Date: Apr 9, 2025
• Publicly Available Date: Apr 10, 2025
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 983
• Issue: 1
• Article Number: 72
• DOI: https://doi.org/10.3847/1538-4357/adc0f9
• Keywords: Galaxies; Damped Lyα systems; Lyα galaxies; Diffuse radiation
• Public URL: https://hull-repository.worktribe.com/output/5127483
• Additional Information: Article Title: Using Lyα Absorption to Measure the Intensity and Variability of z ∼ 2.4 Ultraviolet Background Light; Journal Title: The Astrophysical Journal; Article Type: paper; Copyright Information: © 2025. The Author(s). Published by the American Astronomical Society.; Date Received: 2024-12-09; Date Accepted: 2025-03-13; Online publication date: 2025-04-08