Mapping the "invisible" circumgalactic medium around a z $\sim$ 4.5 radio galaxy with MUSE

TL;DR

This study uses MUSE spectroscopy to map the Lyα halo and HI absorption around a high-redshift radio galaxy, revealing outflowing, metal-enriched gas likely driven by past AGN activity and interacting with the radio jet.

Contribution

First detailed mapping of the circumgalactic medium around a z~4.5 radio galaxy, linking HI absorption features to AGN-driven outflows and jet interactions.

Findings

Detected a large, high-column-density HI absorber with a velocity gradient.

Identified metal-enriched outflowing shell influenced by past AGN activity.

Provided evidence of AGN feedback redistributing gas and metals in early massive galaxies.

Abstract

In this paper we present Multi Unit Spectroscopic Explorer (MUSE) integral field unit spectroscopic observations of the $\sim70\times30$ kpc$^2$ Ly$\alpha$ halo around the radio galaxy 4C04.11 at $z = 4.5077$. High-redshift radio galaxies (HzRGs) are hosted by some of the most massive galaxies known at any redshift and are unique markers of concomitant powerful active galactic nucleus (AGN) activity and star formation episodes. We map the emission and kinematics of the Ly$\alpha$ across the halo as well as the kinematics and column densities of eight HI absorbing systems at $-3500 < \Delta v < 0$ km s$^{-1}$. We find that the strong absorber at $\Delta v \sim 0\,\rm km\,s^{-1}$ has a high areal coverage ($30\times30$ kpc$^2$), being detected across a large extent of the Ly$\alpha$ halo, a significant column density gradient along the southwest to northeast direction, and a velocity gradient along the radio jet axis. We propose that the absorbing structure, which is also seen in CIV and NV absorption, represents an outflowing metal-enriched shell driven by a previous AGN or star formation episode within the galaxy and is now caught up by the radio jet, leading to jet-gas interactions. These observations provide evidence that feedback from AGN in some of the most massive galaxies in the early Universe may play an important role in redistributing material and metals in their environments.