Mapping the dynamics of a giant Ly alpha halo at z = 4.1 with MUSE: the energetics of a large-scale AGN-driven outflow around a massive, high-redshift galaxy

Abstract

We present Multi Unit Spectroscopic Explorer (MUSE) integral field unit spectroscopic observations of the ∼150 kpc Lyα halo around the z = 4.1 radio galaxy TN J1338−1942. This 9-h observation maps the full two-dimensional kinematics of the Lyα emission across the halo, which shows a velocity gradient of Δv ∼ 700 km s−1 across 150 kpc in projection, and also identified two absorption systems associated with the Lyα emission from the radio galaxy. Both absorbers have high covering fractions (∼1) spanning the full ∼150 × 80 kpc2 extent of the halo. The stronger and more blueshifted absorber (Δv ∼ −1200 km s−1 from the systemic) has dynamics that mirror that of the underlying halo emission and we suggest that this high column material (n(H I) ∼ 1019.4 cm−2), which is also seen in C IV absorption, represents an outflowing shell that has been driven by the active galactic nuclei (AGN) or the star formation within the galaxy. The weaker (n(H I) ∼ 1014 cm−2) and less blueshifted (Δv ∼ −500 km s−1) absorber most likely represents material in the cavity between the outflowing shell and the Lyα halo. We estimate that the mass in the shell must be ∼1010 M⊙ – a significant fraction of the interstellar medium from a galaxy at z = 4. The large scales of these coherent structures illustrate the potentially powerful influence of AGN feedback on the distribution and energetics of material in their surroundings. Indeed, the discovery of high-velocity (∼1000 km s−1), group-halo-scale (i.e. >150 kpc) and mass-loaded winds in the vicinity of the central radio source is in agreement with the requirements of models that invoke AGN-driven outflows to regulate star formation and black hole growth in massive galaxies.