Scaling relations of star-forming regions: from kpc-sized clumps to H II regions

Abstract

We present the properties of eight star-forming regions, or 'clumps,' in three galaxies at z ∼ 1.3 from the WiggleZ Dark Energy Survey, which are resolved with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) integral field spectrograph. Within turbulent discs, σ ∼ 90 km s^−1, clumps are measured with average sizes of 1.5 kpc and average Jeans masses of 4.2 × 10^9 M_⊙, in total accounting for 40–60 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 H_II regions are found to follow tight scaling relations over the range z = 0–2 for Hα size, velocity dispersion, luminosity and mass when comparing >2000 H_II regions locally and 30 clumps at z > 1 (σ ∝ r^(0.42 ±0.03), L_(Hα) ∝ r^(2.72 ±0.04), L_(Hα) ∝ σ^(4.18 ±0.21) and L_Hα ∝ 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.

Files

Additional details