Investigating the role of turbulence in the interstellar medium in z ∼ 3 dusty star-forming galaxies using kpc-resolution ALMA dust and gas maps

ABSTRACT We present ALMA high-resolution ($\sim 0.25 \, \mathrm{ arcsec}/2\, \rm {kpc}$) CO(5–4) and CO(4–3) observations of three $z\sim 3$ submillimetre-selected dusty galaxies from the ALESS survey. These data complement existing (sub)-kpc scale ALMA 870 μm continuum imaging and JWST NIRCam and MIRI imaging from the ALESS-JWST program, allowing us to trace the molecular gas, dust-obscured star formation, and stellar populations on similar spatial scales. We spectroscopically confirm that two of the sources lie at the same redshift and are likely interacting. We find that the molecular-gas distribution broadly follows the dusty star-forming structures seen in the 870 μm dust continuum imaging, but that the gas reservoirs are significantly more extended than the dust emission with a spatial extent comparable to the rest-frame near-infrared stellar emission. By modelling the kinematics for the two highest signal-to-noise sources, we find that the galaxies are well-fit by rotating disc models with high ratios of ordered-to-random motion ($V_{\rm {max}}\, /\, \overline{\sigma }=5\pm 1$ and $6\pm 1$), although smaller-scale kinematic deviations cannot be ruled out at the current sensitivity and spatial resolution. Finally, utilizing the high-resolution 870 μm dust continuum and CO data, we investigate star formation scaling relations on kpc-scales in these high-redshift galaxies. Assuming a constant CO-to-H$_{2}$ conversion factor and excitation ratio, we find that the data are offset from theoretical star formation relation predictions that do not take turbulence into account, but consistent with gravo-turbulent models, thereby suggesting that turbulence plays a central role in regulating star formation at high redshift.