The MUSE view of Lyman-$\alpha$ nebulae in High redshift Radio Galaxies

TL;DR

This study uses VLT/MUSE integral field spectroscopy to analyze Ly$ ext{alpha}$ nebulae around high-redshift radio galaxies, revealing their morphology, ionization sources, and weak correlations with radio emission, enhancing understanding of galaxy environments at early cosmic times.

Contribution

First comprehensive MUSE-based analysis of Ly$ ext{alpha}$ nebulae in high-redshift radio galaxies, expanding sample coverage and providing detailed kinematic and ionization insights.

Findings

Ly$ ext{alpha}$ surface brightness profiles are exponential with scale lengths of 20-30 ckpc.

Most nebulae are ionized by AGN activity, with one showing signs of star formation.

Weak correlation between radio and Ly$ ext{alpha}$ luminosities; alignment likely due to anisotropic emission.

Abstract

We present the results of VLT/MUSE integral field spectroscopic observations of the Ly$\alpha\,$ emission nebulae associated with 11 high redshift ($z \geq 2.9$) radio galaxies (HzRGs) with DEC $<25^{\circ}$. When considering the other nine sources with available archival MUSE data, these observations increase the coverage to half of the currently known HzRGs. For two sources we are unable to confirm the original identification, as no Ly$\alpha\,$ emission was detected. We produce narrow band images centered on the Ly$\alpha\,$ line, extract their nuclear spectra, map their ionized gas kinematics, and derive the Ly$\alpha\,$ surface brightness profiles (SBPs). The SBPs are generally well reproduced by an exponential law with a typical scale length of $\sim 20-30$ ckpc. We measure emission line ratios finding most sources in agreement with an AGN origin for their gas ionization, with a single object hinting at strong star formation. Regarding the connection between the radio and ionized gas emission, we find that while the Ly$\alpha\,$ nebulae are preferentially aligned with the direction of the radio emission, there is no clear correlation in terms of size or gas kinematics, and only a weak trend connecting their radio and Ly$\alpha\,$ luminosities. The alignment is most likely the result of anisotropic nuclear emission rather than of a direct impact of the jets into the ionized gas.