The WISSH quasars project. VII. Outflows and metals in the circum-galactic medium around the hyper-luminous z~3.6 quasar J1538+08

Context. In recent 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 a repository for intergalactic and galactic baryons as well as a venue of feeding and feedback processes. The most luminous quasars are privileged test-beds to study these processes, given their large ionising fluxes and dense CGM environments in which they are expected to be embedded.Aims. We aim to characterise the rest-frame ultraviolet (UV) emission lines in the CGM around a hyper-luminous, broad emission line, radio-quiet quasar at z similar to 3.6, which exhibits powerful outflows at both nuclear and host galaxy scales.Methods. We analyse VLT/MUSE observations of the quasar J1538+08 (L-bol=6x10(47) erg s(-1)), and we performed a search for extended UV emission lines to characterise its morphology, emissivity, kinematics, and metal content.Results. We report the discovery of a very luminous (similar to 2x10(44) erg s(-1)), giant Ly alpha nebula and a likely associated extended (75 kpc) CIV nebula. The Ly alpha nebula emission exhibits moderate blueshift (similar to 440 km s(-1)) compared to the quasar systemic redshift and a large average velocity dispersion ( sigma (v) similar to 700 sigma v similar to 700 km s(-1)) across the nebula, while the CIV nebula shows average velocity dispersion of sigma overbar(v) similar to 350 sigma v mml:mo stretchy="false"similar to 350 km 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 the following two Gaussian components: a narrow (sigma similar to 470 km s(-1)) systemic one plus a broad (sigma similar to 1200 km s(-1)), blueshifted (similar to 1500 km 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 kiloparsecs.