We previously reported a putative detection of a radio galaxy at z=10.15, selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917-0012, was based upon three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84-115GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, WISE and Herschel Space Observatory in the infrared, as well as <10GHz polarisation and 162MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917-0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917-0012 is at z<3 then it has an extremely unusual nature, and that the more likely solution is that the source lies above z=7.
@article{arxiv.2111.08103,
title = {The Nature and Likely Redshift of GLEAM J0917-0012},
author = {Guillaume Drouart and Nick Seymour and Jess W. Broderick and José Afonso and Rajan Chhetri and Carlos De Breuck and Bjorn Emonts and Tim J. Galvin and Matthew D. Lehnert and John Morgan and Daniel Stern and Joël Vernet and Nigel Wright},
journal= {arXiv preprint arXiv:2111.08103},
year = {2021}
}