Variations in the slope of the resolved star-forming main sequence: a tool for constraining the mass of star-forming regions

TL;DR

This paper investigates how the slope of the resolved star-forming main sequence varies with spatial resolution and star formation time-scales in simulations, proposing a method to constrain the mass of star-forming regions.

Contribution

It demonstrates that the rSFMS slope depends on spatial resolution and time-scales, and introduces a toy model to use this dependence for constraining star-forming clump masses.

Findings

The rSFMS emerges naturally in FIRE-2 simulations.

The slope depends on spatial resolution and star formation time-scales.

A toy model links rSFMS slope to star-forming clump mass.

Abstract

The correlation between galaxies' integrated stellar masses and star formation rates (the `star formation main sequence'; SFMS) is a well-established scaling relation. Recently, surveys have found a relationship between the star formation rate and stellar mass surface densities on kpc and sub-kpc scales (the `resolved SFMS'; rSFMS). In this work, we demonstrate that the rSFMS emerges naturally in FIRE-2 zoom-in simulations of Milky Way-mass galaxies. We make SFR and stellar mass maps of the simulated galaxies at a variety of spatial resolutions and star formation averaging time-scales and fit the rSFMS using multiple methods from the literature. While the absolute value of the SFMS slope depends on the fitting method, the slope is steeper for longer star formation time-scales and lower spatial resolutions regardless of the fitting method employed. We present a toy model that quantitatively captures the dependence of the simulated galaxies' rSFMS slope on spatial resolution and use it to illustrate how this dependence can be used to constrain the characteristic mass of star-forming clumps.