An ALMA sub-kiloparsec test of the Kennicutt--Schmidt relation in a strongly lensed dusty star-forming galaxy at $z\sim2.78$
Year: 2026
Type: preprint
Abstract: [abridged] Star formation is a key process driving galaxy evolution, but understanding how it proceeds within the interstellar medium (ISM) requires resolving cold molecular gas and dust on sub-kpc scales. At z~2-3, near the peak of cosmic star formation, such resolution can generally only be achieved through strong gravitational lensing. We present an ALMA study of SMMJ0658, a 20x-magnified main-sequence star-forming galaxy at z=2.7768 +/- 0.0002, lensed by the Bullet Cluster (z=0.296) into three images. We use 0.2" and 0.6" ALMA Band-3 observations to test the Kennicutt-Schmidt (KS) relation at sub-kpc scales at cosmic noon. Using a JWST-based strong-lensing model of the Bullet Cluster, we reconstruct source-plane CO(3-2) and rest-frame 803um dust-continuum maps down to ~200pc scales. We derive spatially resolved molecular gas and star formation rate surface densities, depletion times, and the scale dependence of the CO-to-dust flux ratio over 200pc-3.2kpc apertures. The 0.2" ALMA data reveal massive, dense star-forming clumps, with Sigma_mol ~1.3-2.3 x 10^3 M_sun pc^-2, Sigma_SFR ~0.5-2.3 M_sun yr^-1 kpc^-2, and tau_dep ~0.82-2.56 Gyr. CO-dust spatial decorrelation produces a strong scale dependence in tau_dep. We find a KS-relation breakdown scale of 0.8 +/- 0.1 kpc, consistent with individual regions tracing distinct stages of the star-formation cycle. The ALMA and JWST data also reveal evidence for a lensed galaxy pair at z~2.78, although whether SMMJ0658 is undergoing an early-stage interaction remains uncertain. Our results show that the apparent universality of the KS relation breaks down once individual star-forming regions are spatially resolved, in line with observations from the local universe to z~1. We extend this picture to z~2.78, providing new insight into the resolved properties of the clumpy cold ISM and the star-formation cycle at cosmic noon.
Source: arXiv (Cornell University)
Institutions: University of Valparaíso, University of Liège, University of Ljubljana, Centre National de la Recherche Scientifique, Université Côte d'Azur, Lagrange Laboratory, Observatoire de la Côte d’Azur, University of Florida, Universidad Nacional Autónoma de México, National Institute of Astrophysics, Optics and Electronics, Universidad Central de Chile
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, Space Telescope Science Institute, National Radio Astronomy Observatory, Agence Nationale de la Recherche, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, Agencia Nacional de Investigación y Desarrollo, National Institutes of Natural Sciences
Awards: G103270039, VOSS: Research on the Process of Virtual Research Environment, THE INTERSTELLAR PHYSICS OF NORMAL GALAXIES AS REVEALED BY ALMA, G256731684, G4704682132, MILLENIUM NUCLEUS FOR GALAXIES, G5568641063, Deciphering the structural evolution of distant galaxies with CIGALE-2D, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA), G8800819381, G880779785
OpenAlex ID: W7215069159