Early Results from GLASS-JWST. III. Galaxy Candidates at z ∼9-15*

We present the results of a first search for galaxy candidates at z similar to 9-15 on deep seven-band NIRCam imaging acquired as part of the GLASS-James Webb Space Telescope (JWST) Early Release Science Program on a flanking field of the Frontier Fields cluster A2744. Candidates are selected via two different renditions of the Lyman-break technique, isolating objects at z similar to 9-11, and z similar to 9-15, respectively, supplemented by photometric redshifts obtained with two independent codes. We find five color-selected candidates at z > 9, plus one additional candidate with photometric redshift z (phot) >= 9. In particular, we identify two bright candidates at M (UV) similar or equal to -21 that are unambiguously placed at z similar or equal to 10.6 and z similar or equal to 12.2, respectively. The total number of galaxies discovered at z > 9 is in line with the predictions of a nonevolving luminosity function. The two bright ones at z > 10 are unexpected given the survey volume, although cosmic variance and small number statistics limits general conclusions. This first search demonstrates the unique power of JWST to discover galaxies at the high-redshift frontier. The candidates are ideal targets for spectroscopic follow-up in Cycle-2.

Automated summary

In this study, we present the results of a search for galaxy candidates with redshifts around z=9-15 using deep seven-band NIRCam imaging from the GLASS-JWST Early Release Science Program. We identified several candidates using different versions of the Lyman-break technique and obtained their photometric redshifts. These candidates include two bright galaxies with redshifts greater than z=10, which is unexpected given the survey volume.