To see or not to see a z similar to 13 galaxy, that is the question Targeting the [C II] 158 mu m emission line of HD1 with ALMA

Context. Determining when the first galaxies formed remains an outstanding goal of modern observational astronomy. Theory and current stellar population models imply that the first galaxies formed at least at z = 14 15. But to date, only one galaxy at z > 13 (GS-z13-0) has been spectroscopically confirmed. Aims. The galaxy `HD1' was recently proposed to be a z similar to 13:27 galaxy based on its potential Lyman break and tentative [O iii] 88 mu m detection with ALMA. We hereby aim to test this scenario with new ALMA Band 4 observations of what would be the [C II] 158 mu m emission if HD1 is at z similar to 13:27. Methods. We carefully analyse the new ALMA Band 4 observations and re-analyse the existing ALMA Band 6 data on the source to determine the proposed redshift. Results. We find a tentative 4 sigma feature in the Band 4 data that is spatially o ffset by 1:'' 7 and spectrally o ffset by 190 km s(-1) from the previously reported 3.8 sigma `[O III] 88 mu m' feature. Through various statistical tests, we demonstrate that these tentative features are fully consistent with both being random noise features. Conclusions. We conclude that we are more likely to be recovering noise features than both [O III] 88 mu m and [C II] 158 mu m emission from a source at z similar to 13 :27. Although we find no credible evidence of a z similar to 13 :27 galaxy, we cannot entirely rule out this scenario. Non-detections are also possible for a z similar to 13 source with a low interstellar gas-phase metallicity or ionisation parameter and/or high gas density. Moreover, the new continuum and line upper limits provide no strong evidence for or against a lower-redshift scenario. Determining where and exactly what type of galaxy HD1 is, will now likely require JWST /NIRSpec spectroscopy.