We present here the spectrum of the galaxy companion to the z = 4.7 quasar BR1202-0725 , in the optical range 6000 - 9000 Å , corresponding to 1050 - 1580 Å rest–frame .
We detect a strong Ly \alpha emission line at z = 4.702 , with an integrated flux of 2 \times 10 ^ { -16 } ergs cm ^ { -2 } s ^ { -1 } , and a UV continuum longward of the Ly \alpha emission at a flux level of \simeq 3 \times 10 ^ { -19 } ergs cm ^ { -2 } s ^ { -1 } Å ^ { -1 } .
We fail to detect any CIV _ { 1550 } emission with a 3 \sigma upper limit of 3 \times 10 ^ { -17 } ergs cm ^ { -2 } s ^ { -1 } .
We show that the ratio between Ly \alpha and continuum intensity and the absence of a strong CIV emission imply that the UV continuum radiation is the result of an intense star–formation activity rather than of a reprocessing of the QSO flux .
The total estimated SFR of this z = 4.7 star–forming region is \sim 15 - 54 M _ { \odot } yr ^ { -1 } , depending on the IMF and the metallicity .

The present data suggest that the Ly \alpha emission has a velocity and spatial structure , with possible velocity differences of \simeq 500 km s ^ { -1 } on scales of few kpc .
These velocity patterns may be a signature of collapsing or merging phenomena in the QSO and its environment , as expected from current models of galaxy formation at high z .

\keywords Galaxies : formation – intergalactic medium – quasars : individual ( BR 1202 - 0725 )