GBT25B-328

The CNM in the Redshift Desert: First Unambiguous Detection of CRRLs at High z

Abstract

Absorption line systems are important windows into the evolution of galaxies and gas content across cosmic time, serendipitously probing properties of nebulae that might otherwise be too faint to detect in emission. Recently, the first cosmological detections of radio recombination lines (RRLs) (Emig et al. 2019,2023) have been coincident with absorption line systems and are opening up a new avenue for (low frequency, ~< 5 GHz) radio astronomy to investigate gas associated with absorption systems. Using MeerKAT observations, we find evidence for RRL absorption that is coincident with an optical absorption system at z = 1.67 towards PKS 0237-233. Excitedly, this would be just the third non-local detection of RRLs (the highest z yet) and the first that would unambiguously come from carbon RRLs (CRRLs) in the CNM. We propose GBT 800 MHz observations to confirm this feature, as the non-LTE RRL modeling predicts the line amplitude to increase at lower frequencies.

Investigators

Name	Institution
Pedro Salas	Green Bank Observatory
Kimberly Emig *	National Radio Astronomy Observatory
Juan Cardenas	Cornell University

* indicates the PI