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

Abstract: 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 Lyman $\alpha$ 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 $\sim 500$ km s$^-1$) bipolar structure of Lyman $\alpha$ 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 $\sim$ 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$1908 were detected and their line flux ratios determined. The presence of HeII allowed for a precise redshift measurement (z=2.945$\pm$0.002). Along with the recent discovery of a similar structure in TN J1049-1258, another HzRG, it displays the feasibility of using Lyman $\alpha$ 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.