Probing the physical conditions and star formation processes in the
  Galactic HII region S305
  We present multi-scale and multi-wavelength observations of the Galactic HII
region S305, which is excited by massive O8.5V and O9.5V stars. Infrared images
reveal an extended sphere-like shell (extension ~7.5 pc; at T_d = 17.5-27 K)
enclosing the S305 HII region (size ~5.5 pc; age ~1.7 Myr). The extended
structure observed in the Herschel temperature map indicates that the molecular
environment of S305 is heated by the massive O-type stars. Regularly spaced
molecular condensations and dust clumps are investigated toward the edges of
the infrared shell, where the PAH and H_2 emission is also observed. The
molecular line data show a signature of an expanding shell of molecular gas in
S305. GMRT 610 and 1280 MHz continuum maps reveal overdensities of the ionized
emission distributed around two O-type stars, which are surrounded by the
horseshoe envelope (extension ~2.3 pc). A molecular gas deficient region/cavity
is identified toward the center of the horseshoe envelope, which is well traced
with PAH, H_2, molecular, and dust emission. The edges of the infrared shell
are found to be located in the front of the horseshoe envelope. All these
outcomes provide the observational evidence of the feedback of O-type stars in
S305. Moreover, non-thermal radio emission is detected in S305 with an average
spectral index alpha ~-0.45. The variations in alpha, ranging from -1.1 to 1.3,
are explained due to soft synchrotron emission and either optically-thicker
thermal emission at high frequencies or a suppression of the low-frequency
emission by the Razin-Tsytovich effect.
