ALMA observations of super-early galaxies: Attenuation-free model predictions

The abundance and blue color of the super-early (redshift z > 10) luminous galaxies discovered by the James Webb Space Telescope (JWST) can be explained if radiation-driven outflows have ejected their dust on kiloparsec-scales. To test this hypothesis, we predict the Atacama Large Millimeter Array (ALMA) detectability of this extended dust component. Based on the observed properties of the galaxy, its observed continuum flux at 88 µm, F88, depends on the dust-to-stellar mass ratio, ξd, and on the extent of the dust distribution, rd. When this is applied to the most distant known galaxy, GS-z14-0 at z = 14.32, the fiducial model (ξd = 1/529) predicts F88fid = 14.9 µJy and a dust extent rd = 1.4 kpc. If the galaxy is very dust rich (ξd = 1/40), F88max = 40.1 µJy. These values are lower (F88fid = 9.5 µJy) if the dust is predominantly made of large grains such as those that form in supernova ejecta. Forthcoming ALMA observations might come very close to constraining the fiducial predictions of the outflow-based attenuation-free model. Other super-early galaxies are predicted to be fainter at 88 µm, mostly because their star formation rate is lower than that of GS-z14-0, with fiducial fluxes in the range 2−5.2 µJy.