Discovery of a z = 6 . 17 galaxy from CFHT and VLT observations ⋆

We report the discovery of a galaxy at a redshift z = 6.17 identified from deep narrow band imaging and spectroscopic follow-up in one of the CFHT-VIRMOS deep survey fields at 0226-04. In addition to the existing deep BVRI images of this field, we obtained a very deep narrow band image at 920 nm with the aim of detecting Lyα emission at redshift ∼ 6.5. Spectroscopic follow-up of some of the candidates selected on the basis of their excess flux in the NB920 filter was performed at the VLT-UT4 with the FORS2 instrument. For one object a strong and asymmetric emission line associated with a strong break in continuum emission is identified as Lyα at z = 6.17. This galaxy was selected from its continuum emission in the 920 nm filter rather than for its Lyα emission, in effect performing a Lyman Break detection at z = 6.17. We estimate a star formation rate of ∼ 10 M ⊙ .yr −1 for this object, with a velocity dispersion ∼ 400 km.s −1. Similarly to other objects at redshifts ∼5–6, this galaxy presents the characteristics of an already fairly evolved object in spite of its young age. The spectroscopic follow-up of other high z galaxy candidates is ongoing .