Local star-forming galaxies build up central mass concentration most actively near $M_{*}=10^{10}M_{\odot}$

TL;DR

This study investigates how star-forming galaxies build central mass concentration, finding the most active build-up occurs near a stellar mass of 10^10 solar masses, with implications for galaxy morphology evolution.

Contribution

It provides the first detailed analysis of stellar age gradients across a large sample of low-redshift star-forming galaxies, revealing the mass regime of most active central mass build-up.

Findings

Peak fraction (~40%) of galaxies with positive age gradients at M* ~ 10^10 M_sun.

Galaxies with positive gradients are more compact and have centrally concentrated star formation.

Central mass build-up activity is most prominent near M* = 10^10 M_sun.

Abstract

To understand in what mass regime star-forming galaxies (SFGs) build up central mass concentration most actively, we present a study on the luminosity-weighted stellar age radial gradient ($\nabla_{\rm age}$) distribution of $\sim3600$ low-redshift SFGs using the MaNGA Pipe3D data available in the SDSS DR17. The mean age gradient is negative, with $\nabla_{\rm age}=-0.14$log Gyr/$R_{\rm e}$, consistent with the inside-out disk formation scenario. Specifically, SFGs with positive $\nabla_{\rm age}$ consist of $\sim 28\%$ at log$(M_{*}/M_{\odot})<9.5$, while this fraction rises up to its peak ($\sim 40\%$) near log$(M_{*}/M_{\odot})=10$ and then decreases to $\sim 15\%$ at log$(M_{*}/M_{\odot})=11$. At fixed $M_{*}$, SFGs with positive $\nabla_{\rm age}$ typically have more compact sizes and more centrally concentrated star formation than their counterparts, indicative of recent central mass build-up events. These results suggest that the build-up of central stellar mass concentration in local SFGs is mostly active near $M_{*}=10^{10}M_{\odot}$. Our findings provide new insights on the origin of morphological differences between low-mass and high-mass SFGs.