Large expanding molecular arc in the Sagittarius Bl complex

Results of molecular line observations toward the Sagittarius B1 complex are reported. Maps of the HCN, HCO₊ and SiO J = 1-0 emissions were taken with the NRO 45-m telescope. With these data, combined with the ASTE CO J = 3-2 survey data, we have investigated the spatial structure, kinematics and physical conditions of two peculiar molecular features: CO0.55+0.07 and SiO0.56-0.01. The CO arc, CO0.55+0.07, shows clear expanding motion with sizes of 8.5 × 6.8 pc² and an expansion velocity of 40 km s ^-1. The SiO shell, SiO0.56-0.01, has a size of 3.0×3.4 pc ², and surrounds an X-ray Fe line source, GO.570-0.018. The mass and the kinetic energy of CO0.55+0.07 are estimated to be 10^5.5M⊙ and 10^51.5erg, respectively. The kinetic energy of SiO0.56-0.01 is ∼ 10^50.4erg. An LVG analysis shows that the typical density and kinetic temperature are 10^3.8 cm^-3 and 28 K, respectively. High-density clumps with a density of 10^4.0-4.5 cm^-3 associated with CO0.55+0.07 and SiO0.56-0.01 have been found, supporting the idea that they consist of swept-up material. The huge kinetic energy of CO0.55+0.07 is considered to be injected by a series of supernova explosions that took place within ∼ 2× 10⁵yr, which would suggest that it is a 'bubble' created by a massive stellar cluster, whose mass is estimated to be 10^3.5-4.5 M⊙. The origin of SiO0.56-0.01 is rather unclear, but we suggest that it could be related to the X-ray source G0.570-0.018.