Characterizing the Environment Around The Most Distant Known Galaxy

The discovery of the very luminous galaxy GN-z11 at only 400 Myr after the Big Bang in the GOODS-North field with an HST grism spectroscopic redshift of z=11.1+/-0.1 presents a real puzzle for early Universe science. Its detection raises significant questions about our understanding of early galaxy formation, as theoretical models did not predict any such galaxy in the small HST survey area. However, models do predict that the most luminous early galaxies form in the most massive halos, such that they should be significantly clustered, and surrounded by fainter neighbors. Two promising neighbor candidates have already been identified: one lower S/N source seen in HST imaging and one candidate from a NOEMA [CII] emission line search. Clearly, the GOODS-N field around GN-z11 represents the best chance to identify a larger number of z 11 sources that can immediately be followed up with JWST spectroscopy from day one. But already now, GN-z11 provides a unique window deep into cosmic dawn, before reionization occurs - an epoch we thought was inaccessible before JWST. Here, we thus propose one pointing of deeper WFC3/IR imaging in three filters to fully characterize the z 11 environment around GN-z11 and to confirm its neighbor candidate galaxies. At the same time, these data will further constrain the morphology of GN-z11, and enhance the HST legacy in the prime extragalactic field GOODS-North for the JWST era.