2023A&A...669L...8P

A number of new z > 11 galaxy candidates have recently been identified based on public James Webb Space Telescope (JWST) NIRCam observations. Spectroscopic confirmation of these candidates is necessary to robustly measure their redshift and put them in the context of our understanding of the buildup of galaxies in the early Universe. GLASS-z13 is one of these candidates, with a reported photometric redshift z > 11.9. I present publicly available Atacama Large Millimeter/submillimeter Array (ALMA) band 6 Director's Discretionary Time observations (project 2021.A.00020.S; PI T. Bakx), taken to acquire a spectroscopic redshift for GLASS-z13 by searching for [O III] 88 μm line emission in the redshift range z = 11.9 - 13.5. No [O III] 88 μm emission is detected in integrated spectra extracted within an aperture around GLASS-z13, nor when using an automated line finding algorithm (applying different uv-weighting strategies for the imaging). In addition, 1.2 mm continuum emission associated with GLASS-z13 is not detected either. If GLASS-z13 is at z ≈ 12 - 13, this implies a 3-σ upper limit on the [O III] 88 μm and rest-frame ∼90 μm continuum emission of ∼1 × 10⁸ L_⊙ and 10.8 μJy, respectively. The non-detection of [O III] 88 μm and continuum emission does not necessarily imply that GLASS-z13 is not at z ≈ 12 - 13. It can also be explained by a low metallicity (∼0.2 Z_⊙ or lower) and/or high-density (at least 100 cm^–3) interstellar medium. This work demonstrates the synergy between ALMA and JWST to study the properties of the first galaxies; although, JWST/NIRSpec spectroscopy will be necessary to confirm or reject the high photometric redshift of GLASS-z13.