From outside-in to inside-out: galaxy assembly mode depends on stellar mass

TL;DR

This study analyzes how galaxy assembly modes transition from outside-in to inside-out as a function of stellar mass, revealing different color gradient behaviors and quenching processes in low redshift galaxies.

Contribution

It provides observational evidence that galaxy assembly mode depends on stellar mass, with a transition point around 10^{10} to 10^{10.5} solar masses, based on color gradient analysis.

Findings

Low-mass galaxies (<10^{10} M_sun) tend to have positive or flat color gradients.

High-mass galaxies (>10^{10.5} M_sun) mostly show negative color gradients.

The transition in assembly mode correlates with galaxy mass and star formation quenching processes.

Abstract

In this Letter, we investigate how galaxy mass assembly mode depends on stellar mass $M_{\ast}$, using a large sample of $\sim$10, 000 low redshift galaxies. Our galaxy sample is selected to have SDSS $R_{90}>5\arcsec.0$, which allows the measures of both the integrated and the central NUV$-r$ color indices. We find that: in the $M_{\ast}-($ NUV$-r$) green valley, the $M_{\ast}<10^{10}~M_{\sun}$ galaxies mostly have positive or flat color gradients, while most of the $M_{\ast}>10^{10.5}~M_{\sun}$ galaxies have negative color gradients. When their central $D_{n}4000$ index values exceed 1.6, the $M_{\ast}<10^{10.0}~M_{\sun}$ galaxies have moved to the UV red sequence, whereas a large fraction of the $M_{\ast}>10^{10.5}~M_{\sun}$ galaxies still lie on the UV blue cloud or the green valley region. We conclude that the main galaxy assembly mode is transiting from "the outside-in" mode to "the inside-out" mode at $M_{\ast}< 10^{10}~M_{\sun}$ and at $M_{\ast}> 10^{10.5}~M_{\sun}$. We argue that the physical origin of this is the compromise between the internal and the external process that driving the star formation quenching in galaxies. These results can be checked with the upcoming large data produced by the on-going IFS survey projects, such as CALIFA, MaNGA and SAMI in the near future.