Elevation or Suppression? The Resolved Star Formation Main Sequence of Galaxies with Two Different Assembly Modes

TL;DR

This study uses integral field spectroscopy to analyze the spatially-resolved star formation main sequence in galaxies, revealing differences based on their assembly modes and suggesting universal regulation mechanisms.

Contribution

It introduces the concept of the Sub-Galactic Main Sequence and demonstrates how galaxy assembly modes influence the resolved star formation relations.

Findings

The resolved star formation main sequence holds down to sub-galactic scales.

Galaxies with different assembly modes show distinct SGMS slopes.

Inner regions of inside-out galaxies are statistically suppressed in star formation.

Abstract

We investigate the spatially-resolved star formation main sequence in star-forming galaxies (SFGs) using Integral Field Spectroscopic (IFS) observations from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. We demonstrate that the correlation between the stellar mass surface density ($\Sigma_*$) and star formation rate surface density ($\Sigma_{\mathrm{SFR}}$) holds down to sub-galactic scale, leading to the Sub-Galactic Main Sequence (SGMS). By dividing galaxies into two populations based on their recent mass assembly modes, we find the resolved main sequence in galaxies with 'outside-in' mode is steeper than that in galaxies with 'inside-out' mode. This is also confirmed on a galaxy-by-galaxy level, where we find the distributions of SGMS slopes for individual galaxies are clearly separated for the two populations. When normalizing and stacking the SGMS of individual galaxies on one panel for the two populations, we find the inner regions of galaxies with 'inside-out' mode statistically exhibit a suppression in star formation, with a less significant trend in the outer regions of galaxies with 'outside-in' mode. In contrast, the inner regions of galaxies with 'outside-in' mode and the outer regions of galaxies with 'inside-out' mode follow a slightly sub-linear scaling relation with a slope $\sim$0.9, which is in good agreement with previous findings, suggesting that they are experiencing a universal regulation without influences of additional physical processes.