SCALES. I. Bridging Lensed Clump - Giant Clump Scales in Lensed Galaxies at $z=1-4$

Abstract

Dense star-forming regions in $z>1$ galaxies, often termed 'clumps', have been studied across two distinct regimes of telescope resolution, each motivating interpretations in tension with the other. In the SCALES series (Star-Forming Clumps As Layered Emergent Structures), we aim to connect star-forming structures across scales, from the $\sim 100\mathrm{pc}$ clumps in lensed studies to the $\sim \mathrm{kpc}$-scale ''giant'' clumps in unlensed surveys. In this first paper, we present a difference-of-Gaussian (DoG) decomposition that simultaneously models $\approx 50-400\mathrm{pc}$ (lensed) clumps and $\sim \mathrm{kpc}$-scale component (the extended component, or EC), which would together constitute the giant clumps seen at lower resolution. Here the EC is treated as a scale-separated local background rather than a physical object, absorbing all light that is not a compact clump. Applying this to 23 moderately lensed ($\mu \approx 2-9$) galaxies at $z_{spec}=1-4$ to evaluate clump properties (deferring ECs and giant clumps to SCALES-II), we measure a clump stellar mass function slope of $1.88\pm 0.04$, consistent with the $\approx 2$ expected for hierarchical star formation, and with that of $\sim \mathrm{kpc}$-scale clumps in unlensed galaxies. We also show that empirical correlations of clump surface densities and clump-to-host mass ratio with redshift are exaggerated by redshift-dependent detection bias, so $\approx 50-400\mathrm{pc}$ clumps are largely co-similar across our range ($z=1-4$). Finally, combining clump mass, size and age estimates with literature gas-dispersion measurements at similar scales, we argue that $\sim 100\mathrm{pc}$ clumps are themselves composed of star-cluster-like sub-components at much smaller scales.

arXiv commentSubmitted to ApJ; 36 pages, 21 figures. Companion paper (SCALES.II.) appears on arXiv simultaneously