Extended and broad Ly α 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 similar to 5, revealing a Ly alpha nebula with a maximum projected linear size of similar to 60 kpc around the quasar (down to our 2 sigma SB limit per layer of similar to 9 x 10(-19) erg s(-1) cm(-2) arcsec(-2) for a 1 arcsec(2) aperture). After correcting for the cosmological surface brightness dimming, we find that our nebula, at z similar to 5, has an intrinsically less extended Ly alpha 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 alpha 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 (similar to 10 kpc) of the circumgalactic medium of our source, the velocity dispersion of the Ly alpha emission is very high (FWHM > 1000 km s(-1)), suggesting that in our case we may be probing outflowing material associated with the quasar.