The Nature and Likely Redshift of GLEAM J0917-0012

TL;DR

This study investigates the redshift and nature of GLEAM J0917-0012, using multi-wavelength observations and modeling to determine whether it is a high-redshift galaxy or has an unusual low-redshift nature.

Contribution

The paper provides a comprehensive multi-wavelength analysis and modeling approach to constrain the redshift and physical characteristics of GLEAM J0917-0012, challenging previous high-redshift claims.

Findings

No emission lines detected in follow-up ALMA and VLA observations.

Data suggests the source is more likely at z>7 rather than z<3.

The source's nature is consistent with a high-redshift galaxy if at z>7.

Abstract

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.