From giant clumps to clouds

Abstract

The clumpy nature of gas-rich galaxies at cosmic noon raises the question of universality of the scaling relations and average properties of the star-forming structures. Using controlled simulations of disk galaxies and varying only the gas fraction, we show that the influence of the galactic environments (large-scale turbulence, tides, and shear) contributes, together with the different regime of instabilities, to setting a diversity of physical conditions for the formation and evolution of gas clumps from low to high gas fractions. However, the distributions of gas clumps at all gas fractions follow similar scaling relations as Larson’s, suggesting the universality of median properties. Yet, we find that the scatter around these relations significantly increases with the gas fraction, allowing for the presence of massive, large, and highly turbulent clouds in gas-rich disks in addition to a more classical population of clouds. Clumps with an excess of mass for their size are slightly denser, more centrally concentrated, and host more abundant and faster star formation. We find that the star formation activity (rate, efficiency, and depletion time) correlates much more strongly with the excess of mass than with the mass itself. Our results suggest the existence of universal scaling relations for gas clumps but with redshift-dependent scatters, which calls for deeper and more complete census of the populations of star-forming clumps and young stellar clusters at cosmic noon and beyond.