Scaling Relations of Star-Forming Regions: from kpc-size clumps to HII regions

TL;DR

This study examines the properties and scaling relations of star-forming regions from high redshift to the present, revealing consistent patterns that suggest common formation processes despite environmental differences.

Contribution

It provides observational evidence that star-forming regions across a wide redshift range follow tight scaling relations, supporting models of turbulence-driven clump formation.

Findings

Clumps have average sizes of 1.5 kpc and Jeans masses of 4.2 x 10^9 solar masses.

Scaling relations between size, luminosity, velocity dispersion, and mass are consistent across z=0 to 2.

Turbulence influences the size and luminosity of star-forming regions, but their formation processes are similar over cosmic time.

Abstract

We present the properties of 8 star-forming regions, or 'clumps,' in 3 galaxies at z~1.3 from the WiggleZ Dark Energy Survey, which are resolved with the OSIRIS integral field spectrograph. Within turbulent discs, \sigma~90 km/s, clumps are measured with average sizes of 1.5 kpc and average Jeans masses of 4.2 x 10^9 \Msolar, in total accounting for 20-30 per cent of the stellar mass of the discs. These findings lend observational support to models that predict larger clumps will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, clumps and HII regions are found to follow tight scaling relations over the range z=0-2 for size, velocity dispersion, luminosity, and mass when comparing >2000 HII regions locally and 30 clumps at z>1 (\sigma \propto r^{0.42+/-0.03}, L(H\alpha) \propto r^{2.72+/-0.04}, L(H\alpha) \propto \sigma^{4.18+/-0.21}, and L(H\alpha) \propto M_{Jeans}^{1.24+/-0.05}). We discuss these results in the context of the existing simulations of clump formation and evolution, with an emphasis on the processes that drive-up the turbulent motions in the interstellar medium. Our results indicate that while the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes govern their formation from high redshift to the current epoch.