A 20 kiloparsec bipolar Lyman α outflow from a radio galaxy at z=2.95

The study of ionized gas kinematics in high-z active galaxies plays a key part in our understanding of galactic evolution, in an age where nuclear activity was widespread and star formation close to its peak. We present a study of TXS 0952-217, a radio galaxy at z = 2.95, using VLT/MUSE integral field optical spectroscopy as part of a project aimed studying of the properties of ionized gas in high redshift radio galaxies (HzRGs). The Ly alpha line profile of this object presents various emission and absorption components. By utilizing Voronoi binning, we obtained a comprehensive map of the kinematic properties of these components. These observations revealed the presence of a redshifted, high velocity (v similar to 500 km s(-1)) bipolar structure of Ly alpha emission, most likely corresponding to an outflow of ionized gas. The outflow extends beyond the compact radio source on both sides, with a total size of similar to 21 kpc. Its kinetic power (10(42.1) erg s(-1)) is about five orders of magnitude smaller than its radio power. Additional ionized lines, including HeII lambda 1640, CIV lambda 1550 and CIII]lambda 1908 were detected and their line flux ratios determined. The presence of HeII allowed for a precise redshift measurement (z = 2.945 +/- 0.002). Along with the recent discovery of a similar structure in TN J1049-1258, another HzRG, it displays the feasibility of using Ly alpha as a tracer of outflowing gas in high redshift sources, and particularly so when supported by non-resonant ionized lines such as HeII, which allow for accurate redshift and velocity measurements.