Context : During the last years , Ly \alpha nebulae have been routinely detected around high redshift , radio - quiet quasars thanks to the advent of the highly sensitive integral field spectrographs .
Constraining the physical properties of the Ly \alpha nebulae is crucial for a full understanding of the circum-galactic medium ( CGM ) .
The CGM acts both as repository for intergalactic/galactic baryons and a venue of feeding and feedback processes .
The most luminous quasars are privileged test-beds to study these processes , given their large ionizing fluxes and dense CGM environments in which they are expected to be embedded .

Aims : We aim at characterizing the rest-frame ultra-violet ( UV ) emission lines in the CGM around a hyper-luminous , broad emission line , radio-quiet quasar at z \sim 3.6 , that exhibits a powerful outflows at both nuclear and host galaxy scales .

Methods : We analyse VLT/MUSE observations of the quasar J1538+08 ( L _ { bol } = 6 \times 10 ^ { 47 } \leavevmode \nobreak erg \leavevmode \nobreak s ^ { -1 } ) and perform a search for extended UV emission lines to characterize its morphology , emissivity , kinematics and metal content .

Results : We report the discovery of a very luminous ( \sim 2 \times 10 ^ { 44 } \leavevmode \nobreak erg \leavevmode \nobreak s ^ { -1 } % \leavevmode \nobreak cm ^ { -2 } ) , giant ( 150 kpc ) Ly \alpha nebula and a likely associated extended ( 75 kpc ) CIV nebula .
The Ly \alpha nebula emission exhibits moderate blueshift ( \sim 440 \leavevmode \nobreak km \leavevmode \nobreak s ^ { -1 } ) compared with the quasar systemic redshift and a large average velocity dispersion ( \bar { \sigma _ { v } } \sim 700 \leavevmode \nobreak km \leavevmode \nobreak s ^ { % -1 } ) across the nebula , while the CIV nebula shows average velocity dispersion \bar { \sigma _ { v } } \sim 350 \leavevmode \nobreak km \leavevmode \nobreak % s ^ { -1 } .
The Ly \alpha line profile exhibits a significant asymmetry towards negative velocity values at 20 - 30 kpc south of the quasar and is well parametrised by two Gaussian components : a narrow ( \sigma \sim 470 \leavevmode \nobreak km \leavevmode \nobreak s ^ { -1 } ) systemic one plus a broad ( \sigma \sim 1200 \leavevmode \nobreak km \leavevmode \nobreak s ^ { -1 } ) , blueshifted ( \sim 1500 \leavevmode \nobreak km \leavevmode \nobreak s ^ { -1 } ) one .

Conclusions : Our analysis of the MUSE observation of J1538+08 reveals metal-enriched CGM around this hyper-luminous quasar .
Furthermore , our detection of blueshifted emission in the emission profile of the Ly \alpha nebula suggests that powerful nuclear outflows can propagate through the CGM over tens of kpc .