Dominant Role of Coplanar Inflows in Driving Disk Evolution Revealed by Gas-Phase Metallicity Gradients

TL;DR

This study uses spatially resolved spectroscopic data to show that coplanar gas inflow, rather than independent regional evolution, primarily drives the formation and metallicity gradients of galactic disks.

Contribution

It provides observational evidence that coplanar gas inflow is the dominant process influencing disk metallicity gradients, challenging models of independent regional evolution.

Findings

Metallicity gradients strongly correlate with local gas-phase metallicity.

Weak correlation between stellar mass surface density gradients and metallicity gradients.

Metallicity gradients are closely linked to local gas turbulence indicators.

Abstract

Using spatially resolved spectroscopic data from the MaNGA sample, we investigate the parameters influencing the radial gradients of gas-phase metallicity ($\nabla\log(\mathrm{O/H})$), to determine whether disk formation is primarily driven by coplanar gas inflow or by the independent evolution of distinct regions within the disk. Our results show that $\nabla \log(\mathrm{O/H})$ strongly correlates with local gas-phase metallicity at a given stellar mass, with steeper gradients observed in metal-poorer disks. This trend supports the coplanar gas inflow scenario, wherein the gas is progressively enriched by in situ star formation as it flows inward. In contrast, the radial gradient of stellar mass surface density shows very weak correlations with $\nabla \log(\mathrm{O/H})$, which is inconsistent with the independent evolution mode, where gas inflow, star formation, and metal enrichment occur independently within each annulus of the disk. Furthermore, we find that $\nabla \log(\mathrm{O/H})$ is also closely correlated with an indicator of local gas turbulence $\sigma_{\mathrm{gas}}/R_{\mathrm{e}}$, highlighting the competing roles of turbulence and coplanar inflow in shaping metallicity gradients. Our results provide indirect observational evidence supporting coplanar gas inflow as the driving mechanism for disk evolution.