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

Abstract

The southern Galactic high-mass star-forming region, G351.63−1.25, is an H ii region–molecular cloud complex with a luminosity of ∼2.0 × 10⁵ L_⊙, located at a distance of 2.4 kpc from the Sun. In this paper, we focus on the investigation of the associated H ii region, embedded cluster and the interstellar medium in the vicinity of G351.63−1.25. We address the identification of exciting source(s) as well as the census of the stellar populations, in an attempt to unfold star formation activity in this region. The ionized gas distribution has been mapped using the Giant Metrewave Radio Telescope, India, at three frequencies: 1280, 610 and 325 MHz. The H ii region shows an elongated morphology and the 1280 MHz map comprises six resolved high-density regions encompassed by diffuse emission spanning 1.4 × 1.0 pc². Based on the measurements of flux densities at multiple radio frequencies, the brightest ultracompact core has electron temperature T_e∼7647 ±153 K and emission measure, EM∼2.0 ± 0.8×10⁷ cm⁻⁶ pc. The zero-age main-sequence spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHK_s bands using the SIRIUS camera on the 1.4 m Infrared Survey Facility 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 per cent. These indicate that the age of the cluster is consistent with ∼1 Myr. Other available data of this region show that the warm (mid-infrared) and cold (millimetre) dust emission peak at different locations indicating progressive stages of star formation process. 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.