Massive star clusters in high-redshift star-forming galaxies seen at a 100 pc scale thanks to strong gravitational lensing

摘要

High-resolution imaging reveals clumpy morphologies among z= 1 — 3 galaxies. Most of these galaxies are dominated by disk rotation, which led to conclude that the observed clumps are generated from disk fragmentation due to gravitational instability. Despite the kpcscale resolution attained by the most advanced facilities and numerical simulations, these clumps are barely resolved at z> 1. Thanks to the stretching and magnification power provided by gravitational lensing, we reach the sub-kpc resolving power to unveil their physics. From our literature compilation of data, we show that without lensing there is a bias toward clumps with high masses and sizes. The high-redshift clumps identified in lensed galaxies have stellar masses 2 orders of magnitude lower and a median size of 250 pc. They resemble local star clusters observed in the most intensively star-forming galaxies. The clump masses and sizes observed in lensed galaxies agree with new simulations, which show that the Toomre instability criterion overestimates the clump masses by a factor of 5 — 6.