Discovery of a z = 6.17 galaxy from CFHT and VLT observations

Abstract

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 and not from its Lyα emission, in effect performing a Lyman Break detection at z = 6.17. We estimate a star formation rate of several tens of M⊙yr-1 for this object, with a velocity dispersion ∼400 kms-1. The spectroscopic follow-up of other high z galaxy candidates is on-going.