Kavli Affiliate: Jinyi Shangguan
| Summary:
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 $sim100,mathrmpc$ clumps in lensed studies to the $simmathrmkpc$-scale ”giant” clumps in unlensed surveys. In this first paper, we present a difference-of-Gaussian (DoG) decomposition that simultaneously models $approx 50-400,mathrmpc$ (lensed) clumps and $simmathrmkpc$-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 ($μapprox 2-9$) 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 $approx2$ expected for hierarchical star formation, and with that of $simmathrmkpc$-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 $approx 50-400,mathrmpc$ 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 $sim100,mathrmpc$ clumps are themselves composed of star-cluster-like sub-components at much smaller scales.
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