# The dust-continuum size of TNG50 galaxies at $z=1-5$: a comparison with the distribution of stellar light, stars, dust and H$_2$

**Authors:** Gergö Popping, Annalisa Pillepich, Gabriela Calistro Rivera, Sebastian Schulz, Lars Hernquist, Melanie Kaasinen, Federico Marinacci, Dylan Nelson, Mark Vogelsberger  
**arXiv:** [2101.12218](https://arxiv.org/abs/2101.12218)  
**Date:** 2021-01-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2101.12218v1/

## Key points

- Dust-continuum half-light radius at 850 μm is 75% larger than stellar half-mass radius
- Dust continuum emission is more compact compared to 1.6 μm (H-band) emission, especially at higher redshifts
- Compactness of dust continuum emission is due to obscuration of stellar light from galaxy centers
- Compact dust continuum emission does not indicate dense central stellar component in galaxies at redshifts > 1
- Dust continuum half-light radius closely traces regions with half of star formation in galaxies
- Single band dust continuum emission can be used as a reliable tracer for locating obscured star formation
- Dust continuum emission exhibits greater compactness compared to H2 mass and underlying dust mass distributions
- Dust continuum strongly correlates with regions characterized by high temperatures but not necessarily where most H2 and/or dust are concentrated
- These findings provide valuable insights into main sequence galaxies and their dust continuum properties

## Summary

In this study, the authors investigate the extent of dust-continuum emission in main-sequence galaxies at redshifts between 1 and 5 using data from the TNG50 simulation. They employ the radiative transfer code SKIRT to model the dust-continuum half-light radius of thousands of galaxies, assuming a Milky Way dust type and a metallicity-dependent dust-to-metal ratio. The results reveal that the dust-continuum half-light radius at an observed-frame wavelength of 850 μm is approximately 75% larger than the stellar half-mass radius. However, it is significantly more compact compared to the observed-frame 1.6 μm (H-band) half-light radius, particularly at higher redshifts. This increased compactness with respect to the 1.6 μm emission is driven by obscuration of stellar light from galaxy centers, which enhances the apparent size of disk structures at shorter wavelengths. Importantly, these findings suggest that the compact dust-continuum emission observed in galaxies at redshifts greater than 1 does not necessarily indicate the presence of a dense central stellar component. Furthermore, it is found that the dust continuum half light radius closely traces regions containing half of star formation in galaxies; thus single band dust continuum emission can serve as a reliable tracer for locating obscured star formation. Additionally, it is noted that compared to both H2 mass (for galaxies at z ≥ 2) and underlying dust mass distributions; dust continuum emission exhibits greater compactness and strongly correlates with regions characterized by high temperatures but does not necessarily coincide with locations where most H2 and/or dust are concentrated. Overall, these results provide valuable insights into main sequence galaxies and highlight common features regarding their dust continuum properties.