Tentative rotation in a galaxy at z ~ 14 with ALMA

We reanalysed the Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [O III] λ88 μm emission line in JADES-GS-z14-0, so one of the most distant spectroscopically confirmed galaxies at z = 14.18. Our analysis shows a tentative detection of a velocity gradient of [O III] λ88 μm using three independent tests: (1) construction of moment maps; (2) extraction of integrated spectra from a grid of apertures; and (3) spectro-astrometry in both the image and uv planes, confirming the presence of the velocity gradient at 3σ significance. We performed kinematical fitting using the kinms code and estimated a dynamical mass of log10(Mdyn/M⊙) = 9.4+0.8-0.4, with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion (σv) of <40 km s−1 which results in an estimate of Vrot/σ > 2.5. This result, if confirmed with higher resolution observations, would imply that kinematically cold discs are already in place at z ∼ 14. Comparison with mock observations from the SERRA cosmological simulations confirms that even low-resolution observations are capable of detecting a velocity gradient in z > 10 galaxies as compact as JADES-GS-z14-0. This Letter shows that deeper ALMA or JWST (James Webb Space Telescope)/Near-Infrared Spectrograph integral field spectroscopy observations with high spatial resolution will be able to estimate an accurate dynamical mass for JADES-GS-z14-0, providing an upper limit to the stellar mass of this overluminous galaxy.