The Properties of Massive Star-forming galaxies with Outside-in Assembly
  Mode
  Previous findings show that massive ($> 10^{10} M_{sun}$) star-forming (SF)
galaxies usually have an inside-out stellar mass assembly mode. In this paper,
we have for the first time selected a sample of 77 massive SF galaxies with an
outside-in assembly mode (called targeted sample) from the Mapping Nearby
Galaxies at the Apache Point Observatory (MaNGA) survey. For comparison, two
control samples are constructed from MaNGA sample matched in stellar mass: a
sample of 154 normal SF galaxies and a sample of 62 quiescent galaxies. In
contrast to normal SF galaxies, the targeted galaxies appear to be more
smooth-like and bulge-dominated, and have smaller size, higher concentration,
higher star formation rate and higher gas-phase metallicity as a whole.
However, they have larger size and lower concentration than quiescent galaxies.
Unlike normal SF sample, the targeted sample exhibits a slightly positive
gradient of 4000 \AA\ break and a pronounced negative gradient of H${\alpha}$
equivalent width. Further more, their median surface mass density profile is
between that of normal SF sample and quiescent sample, indicating that the gas
accretion of quiescent galaxies is not likely to be the main approach for the
outside-in assembly mode. Our results suggest that the targeted galaxies are
likely in the transitional phase from normal SF galaxies to quiescent galaxies,
with rapid on-going central stellar mass assembly (or bulge growth). We discuss
several possible formation mechanisms for the outside-in mass assembly mode.
