We present multi-scale and multi-wavelength observations of the Galactic H ii region S305 , which is excited by massive O8.5V and O9.5V stars .
Infrared images reveal an extended sphere-like shell ( extension \sim 7.5 pc ; at T _ { \mathrm { d } } = 17.5–27 K ) enclosing the S305 H ii region ( size \sim 5.5 pc ; age \sim 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 \sim 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 \sim - 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 .