Tentative rotation in a galaxy at z$\sim$14 with ALMA

Abstract

We re-analysed ALMA observations of the [OIII]$\hat{I}»$88$\hat{I}¼$m emission line in JADES-GS-z14.0, so far the most distant spectroscopically confirmed galaxy at z=14.18. Our analysis shows a tentative detection of a velocity gradient of [OIII]$\hat{I}»$88$\hat{I}¼$m using three independent tests: 1) construction of moment maps; 2) extraction of integrated spectra from a grid of apertures; and 3) spectro-astrometry in both the image and uv planes. We performed kinematical fitting using the KinMS code and estimated a dynamical mass of log${}_{10}$(M${}_{\mathrm{dyn}}$/${\mathrm{M}}_{\odot }$)= 9.4${}_{-0.4}^{+0.8}$, with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion ($\ddot{I}{ƒ}_v$) of $<40$ km/s~which results in an estimate of V${}_{\mathrm{rot}}/\ddot{I}ƒ>$ 2.5. This result, if confirmed with higher-resolution observations, would imply that kinematically cold discs are already in place at $z\sim 14$. 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 work shows that deeper ALMA or JWST/NIRSpec IFS 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 over-luminous galaxy.

accepted in Submitted to MNRAS as a letter