Star Formation at z = 4.7 in the Environment of the Quasar BR 1202−07

We present the spectrum of the galaxy companion to the z = 4.7 quasar BR 1202-0725 in the optical range 6000–9000 Å, corresponding to 1050–1580 Å in the rest frame. We detect a strong Lyα emission line at z = 4.702, with an integrated flux of 2 × 10-16 ergs cm-2 s-1, and a UV continuum longward of the Lyα emission at a flux level of ≃3 × 10-19 ergs cm-2 s-1 Å-1. We fail to detect any C IV λ1550 emission with a 3 σ upper limit of 3 × 10-17 ergs cm-2 s-1. We show that the ratio between Lyα and continuum intensity and the absence of strong C IV emission imply that the UV continuum radiation is the result of intense star formation activity rather than of reprocessing of the QSO flux. The total estimated star formation rate of this z = 4.7 star-forming region is ∼15–54 M⊙ yr-1, depending on the initial mass function and the metallicity. The present data suggest that the Lyα emission has a velocity and spatial structure, with possible velocity differences of ≃500 km s-1 on scales of a few kiloparsecs. 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.