The spatial distribution of dust-obscured star-formation in TNG50 main-sequence galaxies
Gergo Popping (ESO (EU ALMA Regional Center)) (CITA)
October 18, 2021
Abstract: The mass-size relation of galaxies and its evolution has been well studied through optical and near-infrared (NIR) imaging. At z>3 these observations correspond to blue rest-frame wavelengths, tracing young stellar populations whose emission is easily absorped by dust. To gain a full census of the distribution of young stars within galaxies it is thus important to also study the resolved dust continuum emission, the dust re-emitted light form young stars, of said galaxies. Now that ALMA has reached its full capabilities, the dust-continuum size of galaxies has been measured for a number of z > 2 sources. It is expected that in the next few years the dust continuum distribution of galaxies will be observed on a more systematic basis accross the star-forming main-sequence and cosmic time. Available observations of SMGs and the most massive main-sequence galaxies have suggested that the sub-mm continuum size of galaxies is smaller than the stellar size, suggesting the buildup of a dust-obscured stellar component. Galaxy formation simulations such as IllustrisTNG50 now have the mass and spatial resolution to provide detailed predictions for the dust-continuum size of thousands of main-sequence galaxies throughout cosmic time and compare these to sizes at any other wavelength and the underlying stellar, gas, SFR and dust distribution. We have obtained resolved dust continuum maps of thousands of main-sequence galaxies from z=1 to z=5 taken from the IllustrisTNG50 simulation, by running the model galaxies through the radiative transfer code SKIRT. In this talk I will present the approach we took and specifically focus on an efficient approach to assign a dust-mass to gas particles when the dust content is not actually tracked within the simulations. I will then show 1) how the dust continuum mass-size relation of galaxies evolves; 2) how the distribution of optical/NIR and dust-continuum emission compares to the distribution of star formation; 3) that the observed dust-continuum emission of z>2 galaxies is more compact than the stellar emission and that this is a common feature for main sequence galaxies, especially for z>3 galaxies; 4) that this is the natural consequence of absorption of rest-frame optical emission by dust, which dramatically changes the optical radial light profile of galaxies, and not necessarily the sign of the buildup of a dust-obscured dense central stellar component. I will finish by discussing the implications of our results, specifically focusing on how to best unravel the distribution of star-formation in high-redshift galaxies and insights for observations with the next generation of 30-meter ground and space-based observatories.