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

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 (${\nabla }_{\mathrm{age}}$) distribution of $\sim 3600$ low-redshift SFGs using the MaNGA Pipe3D data available in the SDSS DR17. The mean age gradient is negative, with ${\nabla }_{\mathrm{age}}=-0.14$log Gyr/$R_{\mathrm{e}}$, consistent with the inside-out disk formation scenario. Specifically, SFGs with positive ${\nabla }_{\mathrm{age}}$ consist of $\sim 28\%$ at log$(M_{\ast }/M_{\odot })<9.5$, while this fraction rises up to its peak ($\sim 40\%$) near log$(M_{\ast }/M_{\odot })=10$ and then decreases to $\sim 15\%$ at log$(M_{\ast }/M_{\odot })=11$. At fixed $M_{\ast }$, SFGs with positive ${\nabla }_{\mathrm{age}}$ 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 $M_{\ast }=10^{10}{M}_{\odot }$. Our findings provide new insights on the origin of morphological differences between low-mass and high-mass SFGs.

10 pages, 8 figures, accepted by ApJ