Spectroscopy of extended Lyα envelopes around z = 4.5 quasars

What are the frequency, shape, kinematics, and luminosity of Lyα envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questions, we have searched for Lyα envelopes around six radio-quiet quasars at z ~ 4.5, using deep spectra taken with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT). Using the multi-slit mode allows us to observe several point spread function stars simultaneously with the quasar, and to remove the point-like emission from the quasar, unveiling the faint underlying Lyα envelope with unprecedented depth. An envelope is detected around four of the six quasars, which suggests that these envelopes are very frequent. Their diameter varies in the range 26 ≲ d ≲ 64 kpc, their surface brightness in the range 3 × 10-19 ≲ μ ≲ 2 × 10-17 erg s-1 cm-2 arcsec-2, and their luminosity in the range 1042 ≲ L(Lyα) ≲ 1044 erg s-1. Their shape may be strongly asymmetric. The Lyα emission line full width at half maximum (FWHM) is 900