Speaker
Description
Neutral atomic hydrogen is the primary raw material from which stars form in galaxies; and understanding its spatial distribution, kinematics, and thermal state across cosmic time is therefore fundamental to our comprehension of how galaxies assemble and evolve. The 21-cm hyperfine transition of neutral hydrogen is a powerful probe of cold gas in and around galaxies across cosmic time. When a radio source lies behind a cloud of neutral hydrogen, the cold gas imprints a characteristic absorption feature in the spectrum of the background source at the redshifted 21-cm frequency. Unlike 21-cm emission, the absorption feature is detectable independently of the distance to the absorber, so its detectability does not diminish with redshift. Despite this advantage, the known sample of extragalactic 21-cm absorbers at redshifts z > 1 has remained small: only 42 systems were known prior to this work, reflecting the scarcity of suitable radio facilities at the relevant frequencies.
In this talk, I present the results of a pilot blind search for 21-cm absorption systems conducted with the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope operating between 400 and 800 MHz, which corresponds to the 21-cm line at redshifts 0.78 < z < 2.55. This pilot survey resulted in the discovery of a new 21-cm absorber at z = 2.327, which is only the fifth known absorber associated with a quasar at z > 2. The survey also recovered two previously known intervening absorbers, validating the detection pipeline.
