Star Formation Rates, Metallicities, and Stellar Masses on kpc-scales in TNG50

TL;DR

This study investigates the spatially-resolved properties of galaxies in the TNG50 simulation, focusing on star formation and metallicity relations at kpc scales, comparing results with observations and exploring underlying physical models.

Contribution

It provides a detailed analysis of resolved star formation and metallicity relations in TNG50, highlighting discrepancies with observations and proposing a leaky-box model for galaxy evolution at kpc scales.

Findings

rSFMS is shallower than observed, likely due to AGN feedback overestimation.

rMZR in TNG50 agrees well with observations.

Resolved relations are consistent with a low net outflow rate in the leaky-box model.

Abstract

Integral field units (IFU) have extended our knowledge of galactic properties to kpc (or, sometimes, even smaller) patches of galaxies. These scales are where the physics driving galaxy evolution (feedback, chemical enrichment, etc.) take place. Quantifying the spatially-resolved properties of galaxies, both observationally and theoretically, is therefore critical to our understanding of galaxy evolution. To this end, we investigate spatially-resolved scaling relations within galaxies of $M_\star>10^{9.0}$ at $z=0$ in IllustrisTNG. We examine both the resolved star-forming main sequence (rSFMS) and the resolved mass-metallicity relation (rMZR) using $1~{\rm kpc}\times1~{\rm kpc}$ maps. We find that the rSFMS in IllustrisTNG is well-described by a power-law, but is significantly shallower than the observed rSFMS. However, the disagreement between the rSFMS of IllustrisTNG and observations is likely driven by an overestimation of AGN feedback in IllustrisTNG for the higher mass hosts. Conversely, the rMZR for IllustrisTNG has very good agreement with observations. Furthermore, we argue that the rSFMS is an indirect result of the Schmidt-Kennicutt (SK) law and local gas relation, which are both independent of host galaxy properties. Finally, we expand upon a localized leaky-box model to study the evolution of idealized spaxels and find that it provides a good description of these resolved relations. The degree of agreement, however, between idealized spaxels and simulated spaxels depends on the `net' outflow rate for the spaxel, and the IllustrisTNG scaling relations indicate a preference for a low net outflow rate.