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

¹ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
² Leiden Observatory, Leiden University, NL-2300 RA Leiden, Netherlands
³ Observatoire de Genève, 1290 Versoix, Switzerland
⁴ Cosmic Dawn Center (DAWN), Niels Bohr Institute, University of Copenhagen, Jagtvej 128, København N DK-2200, Denmark

^⋆ Corresponding author; andrea.ferrara@sns.it

Received: 25 September 2024
Accepted: 14 January 2025

Abstract

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, ξ_d, and on the extent of the dust distribution, r_d. When this is applied to the most distant known galaxy, GS-z14-0 at z = 14.32, the fiducial model (ξ_d = 1/529) predicts F₈₈^fid = 14.9 μJy and a dust extent r_d = 1.4 kpc. If the galaxy is very dust rich (ξ_d = 1/40), F₈₈^max = 40.1 μJy. These values are lower (F₈₈^fid = 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.