Exploring the physical properties of lensed star-forming clumps at 2 ≲ z ≲ 6

We study the physical properties (size, stellar mass, luminosity, and star formation rate) and scaling relations for a sample of 166 star-forming clumps with redshift z similar to 2-6.2. They are magnified by the Hubble Frontier Field galaxy cluster MACS J0416 and have robust lensing magnification (2 less than or similar to mu less than or similar to 82) computed by using our high-precision lens model, based on 182 multiple images. Our sample extends by similar to 3 times the number of spectroscopically confirmed lensed clumps at z greater than or similar to 2. We identify clumps in ultraviolet continuum images and find that, whenever the effective spatial resolution (enhanced by gravitational lensing) increases, they fragment into smaller entities, likely reflecting the hierarchically organized nature of star formation. Kpc-scale clumps, most commonly observed in field, are not found in our sample. The physical properties of our sample extend the parameter space typically probed by z greater than or similar to 1 field observations and simulations, by populating the low mass (M-22c6; less than or similar to 10(7) M-circle dot), low star formation rate (SFR less than or similar to 0.5 M-circle dot yr(-1)), and small size (R-eff less than or similar to 100 pc) regime. The new domain probed by our study approaches the regime of compact stellar complexes and star clusters. In the mass-size plane, our sample spans the region between galaxies and globular clusters, with a few clumps in the region populated by young star clusters and globular clusters. For the bulk of our sample, we measure star formation rates which are higher than those observed locally in compact stellar systems, indicating different conditions for star formation at high redshift than in the local Universe.

Automated summary

This study investigates the physical properties and scaling relations of 166 star-forming clumps at redshifts around 2 to 6.2. The clumps are magnified by the galaxy cluster MACS J0416 and have reliable lensing magnification calculated using a high-precision lens model. The sample extends the scope of previous observations and simulations, and the physical properties of the clumps show differences in star formation conditions between high redshift and the local Universe.