Star formation activity in the southern Galactic HII region G351.63-1.25

The southern Galactic high mass star-forming region, G351.6-1.3, is a HII region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located at a distance of 2.4 kpc. In this paper, we focus on the investigation of the associated HII region, embedded cluster and the interstellar medium in the vicinity of G351.6-1.3. We address the identification of exciting source(s) as well as the census of stellar populations. The ionised gas distribution has been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated morphology and the 1280 MHz map comprises six resolved high density regions encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHKs bands using the SIRIUS instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The near-infrared images reveal the presence of a cluster embedded in nebulous fan-shaped emission. The log-normal slope of the K-band luminosity function of the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the near-infrared excess stars is estimated to be 43%. These indicate that the age of the cluster is consistent with 1 Myr. The champagne flow model from a flat, thin molecular cloud is used to explain the morphology of radio emission with respect to the millimetre cloud and infrared brightness.