A systematic study of Galactic infrared bubbles along the Galactic plane
  with AKARI and Herschel
  Galactic infrared (IR) bubbles, which have shell-like structures in the
mid-IR wavelengths, are known to contain massive stars near their centers. IR
bubbles in inner Galactic regions ($|$l$|\leq$ 65$^{\circ}$, $|$b$|\leq$
1$^{\circ}$) have so far been studied well to understand the massive star
formation mechanisms. In this study, we expand the research area to the whole
Galactic plane (0$^{\circ}\leq$ l $<$360$^{\circ}$, $|$b$|\leq$ 5$^{\circ}$),
using the AKARI all-sky survey data. We limit our study on large bubbles with
angular radii of $>1'$ to reliably identify and characterize them. For the 247
IR bubbles in total, we derived the radii and the covering fractions of the
shells, based on the method developed in \citet{Hattori2016}. We also created
their spectral energy distributions, using the AKARI and Herschel photometric
data, and decomposed them with a dust model, to obtain the total IR luminosity
and the luminosity of each dust component, i.e., polycyclic aromatic
hydrocarbons (PAHs), warm dust and cold dust. As a result, we find that there
are systematic differences in the IR properties of the bubbles between inner
and outer Galactic regions. The total IR luminosities are lower in outer
Galactic regions, while there is no systematic difference in the range of the
shell radii between inner and outer Galactic regions. More IR bubbles tend to
be observed as broken bubbles rather than closed ones and the fractional
luminosities of the PAH emission are significantly higher in outer Galactic
regions. We discuss the implications of these results for the massive stars and
the interstellar environments associated with the Galactic IR bubbles.
