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