Probing gas kinematics and PDR structure around O-type stars in Sh 2-305
  HII region
  We report an observational study of the Galactic HII region Sh 2-305/S305
using the [CII] 158 $\mu$m line data, which are used to examine the gas
dynamics and structure of photodissociation regions. The integrated [CII]
emission map at [39.4, 49.5] km s$^{-1}$ spatially traces two shell-like
structures (i.e., inner and outer neutral shells) having a total mass of
$\sim$565 M$_\odot$. The inner neutral shell encompasses an O9.5V star at its
centre and has a compact ring-like appearance. However, the outer shell is seen
with more extended and diffuse [CII] emission, hosting an O8.5V star at its
centre and surrounds the inner neutral shell. The velocity channel maps and
position-velocity diagrams confirm the presence of a compact [CII] shell
embedded in the diffuse outer shell, and both the shells seem to expand with
$v_{\rm exp}\sim$1.3 km s$^{-1}$. The outer shell appears to be older than the
inner shell, hinting that these shells are formed sequentially. The [CII]
profiles are examined toward S305, which are either double-peaked or
blue-skewed and have the brighter redshifted component. The redshifted and
blueshifted components spatially trace the inner and outer neutral shell
geometry, respectively. The ionized, neutral, and molecular zones in S305 are
seen adjacent to one another around the O-type stars. The regularly spaced
dense molecular and dust clumps (mass $\sim$10-10$^{3}$ M$_{\odot}$) are
investigated around the neutral shells, which might have originated due to
gravitational instability in the shell of collected materials.
