Discovery of a 21 cm absorption system at z=2.327 with CHIME
Abstract
We report the detection of a new 21 cm absorption system associated with the radio source NVSS J164725+375218 at a redshift of z=2.327, identified through a pilot survey conducted by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). This is the fifth detection of an associated system at z > 2. By analyzing a subset of available data, we conduct a spectrally blind survey for 21 cm absorption systems within the redshift range of 0.78 to 2.55 along 202 lines of sight toward known sources in the declination range of 35 to 60 degrees. We detect three 21 cm absorbers: two previously known intervening systems and one newly discovered associated system. By fitting the absorption profiles with models containing one to three Gaussian components and selecting the best model using the Bayesian information criterion, we estimate the optical depth, velocity-integrated optical depth, and the ratio between the HI column density and the spin temperature of the absorption systems. These results demonstrate CHIME's ability to discover new absorbers, even in a small subset of its full dataset.
Cite
@article{arxiv.2506.11269,
title = {Discovery of a 21 cm absorption system at z=2.327 with CHIME},
author = {CHIME Collaboration and Mandana Amiri and Arnab Chakraborty and Simon Foreman and Mark Halpern and Alex S. Hill and Gary Hinshaw and Carolin Hofer and Albin Joseph and Joshua MacEachern and Kiyoshi W. Masui and Juan Mena-Parra and Arash Mirhosseini and Ue-Li Pen and Tristan Pinsonneault-Marotte and Alex Reda and J. Richard Shaw and Seth R. Siegel and Yukari Uchibori and Rik van Lieshout and Haochen Wang and Dallas Wulf},
journal= {arXiv preprint arXiv:2506.11269},
year = {2026}
}
Comments
11 pages, 5 figures, Accepted for publication in ApJ