KMTNet Nearby Galaxy Survey III. Deficient H$\alpha$ flux in the
  Extended Disks of Spiral Galaxies
  We perform a deep wide-field imaging survey of nearby galaxies using
H$\alpha$ and broadband filters to investigate the characteristics of star
formation in galaxies. Motivated by the finding that star formation rates
(SFRs) derived from H$\alpha$ fluxes in dwarf galaxies are systematically lower
than those inferred from far-ultraviolet (FUV) fluxes, we attempt to determine
whether the same trend exists in the extended disks of two star-forming
galaxies. We perform spatially resolved photometry using grid-shaped apertures
to measure the FUV and H$\alpha$ fluxes of star-forming regions. We also
perform spectral energy distribution (SED) fittings using 11 photometric data
(FUV-to-MIR) including data from the literature to estimate the local
properties such as internal attenuation of individual star-forming clumps.
Comparing SFR$_\mathrm{FUV}$ and SFR$_\mathrm{H\alpha}$, which are converted
from the H$\alpha$ and FUV fluxes corrected for the local properties, we find
that SFR$_\mathrm{H\alpha}$/SFR$_\mathrm{FUV}$ tends to decrease as the SFR
decreases. We evaluate possible causes of this discrepancy between the two SFRs
by restricting parameters in the SED fitting and conclude that deficient
H$\alpha$ fluxes in the extended disks of galaxies are tightly correlated with
recent starbursts. The strong and short starburst which is being rapidly
suppressed over the last 10 Myr seems to induce a significant discrepancy
between the SFR$_\mathrm{H\alpha}$ and SFR$_\mathrm{FUV}$. In addition, the
recent bursts in the extended disks of galaxies appear to have occurred
azimuth-symmetrically, implying that these were likely triggered by gas
accretion or internal processes rather than external perturbation.
