Discovery of a 21 cm absorption system at z=2.327 with CHIME

TL;DR

This paper reports the discovery of a new 21 cm absorption system at z=2.327 using CHIME, demonstrating the telescope's capability to identify such systems in a spectrally blind survey across multiple lines of sight.

Contribution

First detection of a 21 cm absorption system at z>2 using CHIME, showcasing its potential for discovering high-redshift absorbers in blind surveys.

Findings

Detected three 21 cm absorbers, including one new associated system.

Successfully modeled absorption profiles with Gaussian components.

Validated CHIME's effectiveness in finding new HI absorption systems.

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.