Extended and broad Ly\u3b1 emission around a BAL quasar at z ~ 5

In this work we report deep MUSE observations of a broad absorption line (BAL) quasar at z ~ 5, revealing a Ly\u3b1 nebula with a maximum projected linear size of ~60 kpc around the quasar (down to our 2\u3c3 SB limit per layer of ~ 9 7 10-19 erg s-1 cm-2 arcsec-2 for a 1 arcsec2 aperture). After correcting for the cosmological surface brightness dimming, we find that our nebula, at z~5, has an intrinsically less extended Ly\u3b1 emission than nebulae at lower redshift. However, such a discrepancy is greatly reduced when referring to comoving distances, which take into account the cosmological growth of dark matter (DM) haloes, suggesting a positive correlation between the size of Ly\u3b1 nebulae and the sizes of DM haloes/structures around quasars. Differently from the typical nebulae around radio-quiet non-BAL quasars, in the inner regions (~10 kpc) of the circumgalactic medium of our source, the velocity dispersion of the Ly\u3b1 emission is very high (FWHM > 1000 km s-1), suggesting that in our case we may be probing outflowing material associated with the quasar