Ikki Mitsuhashi, Jorge A. Zavala, Tom J. L. C. Bakx, Akio K. Inoue, M. Castellano, Antonello Calabrò, Caitlin M. Casey, Maximilien Franco, Bunyo Hatsukade, Nimish P. Hathi, Ryota Ikeda, Anton M. Koekemoer, Jeyhan Kartaltepe, Kirsten Quyen Nguyen Knudsen, Paola Santini, Toshiki Saito, Elena Terlevich, Roberto Terlevich, L. (L.Y.A) Yung
Abstract We investigate the dust mass buildup and star formation efficiency of two galaxies at z > 12—GHZ2 and GS-z14-0—by combining Atacama Large Millimeter/submillimeter Array and JWST observations with an analytical model that assumes dust at thermal equilibrium. We obtained 3 σ constraints on the dust mass of log M dust / M ⊙ < 5.0 and <5.3, respectively. These constraints are in tension with a high dust condensation efficiency in stellar ejecta but are consistent with models with a short metal accretion timescale at z > 12. Given the young stellar ages of these galaxies ( t age ∼ 10 Myr), dust grain growth via accretion may still be ineffective at this stage, though it likely works efficiently to produce significant dust in galaxies at z ∼ 7. The star formation efficiencies, defined as the star formation rate divided by the molecular gas mass, reach ∼10 Gyr −1 over a 10 Myr timescale, aligning with the expected redshift evolution of “starburst” galaxies with efficiencies that are ∼0.5–1 dex higher than those in main-sequence galaxies. This starburst phase seems to be common in UV-bright galaxies at z > 12 and is likely associated with the unique conditions of the early phases of galaxy formation, such as bursty star formation. Direct observations of molecular gas tracers like [C ii ] will be crucial to further understanding the nature of bright galaxies at z > 12.