Massive star formation around IRAS05345+3157 - I. The dense gas

We present observations of the intermediate to massive star-forming region I05345+3157 using the molecular line tracer CS(2-1) with the Combined Array for Research in Millimetre-wave Astronomy to reveal the properties of the dense gas cores. Seven gas cores are identified in the integrated intensity map of CS(2-1). Among these, cores 1 and 3 have counterparts in the λ= 2.7 mm continuum data. We suggest that cores 1 and 3 are star-forming cores that may already or will very soon harbour young massive protostars. The total masses of core 1 estimated from the local thermodynamic equilibrium (LTE) method and dust emission by assuming a gas-to-dust ratio are 5 ± 1 and 18 ± 6M_⊙, and that of core 3 are 15 ± 7 and 11 ± 3M_⊙, respectively. The spectrum of core 3 shows blue-skewed self-absorption, which suggests gas infall - a collapsing core. The observed broad linewidths of the seven gas cores indicate non-thermal motions. These non-thermal motions can be interactions with nearby outflows or due to the initial turbulence; the former is observed, while the role of the initial turbulence is less certain. Finally, the virial masses of the gas cores are larger than the LTE masses, which, for a bound core, implies a requirement on the external pressure of ∼10⁸ K cm^-3. The cores have the potential to further form massive stars.