Chemical properties in the most distant radio galaxy

TL;DR

This study analyzes the chemical composition of the most distant known radio galaxy at z=5.19 using optical spectroscopy, revealing early chemical enrichment with significant carbon and oxygen presence.

Contribution

First detection of CIV emission line in a galaxy at z=5.19, providing new insights into early galaxy chemical evolution.

Findings

Detected CIV emission line from the galaxy's NLR.

Established a lower limit on [C/O] ratio at early cosmic time.

Indicated significant chemical evolution occurred by z=5.19.

Abstract

We present a deep optical spectrum of TN J0924-2201, the most distant radio galaxy at z = 5.19, obtained with FOCAS on the Subaru Telescope. We successfully detect, for the first time, the CIV1549 emission line from the narrow-line region (NLR). In addition to the emission-line fluxes of Ly alpha and CIV, we set upper limits on the NV and HeII emissions. We use these line detections and upper limits to constrain the chemical properties of TN J0924-2201. By comparing the observed emission-line flux ratios with photoionization models, we infer that the carbon-to-oxygen relative abundance is already [C/O] > -0.5 at a cosmic age of ~ 1.1 Gyr. This lower limit on [C/O] is higher than the ratio expected at the earliest phases of the galaxy chemical evolution, indicating that TN J0924-2201 has already experienced significant chemical evolution at z = 5.19.