A Large Expanding Molecular Arc in the Sagittarius B1 Complex

Abstract

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 |$\times$| 6.8 pc|$^2$| and an expansion velocity of 40 km s|$^{-1}$|⁠. The SiO shell, SiO0.56|$-$|0.01, has a size of 3.0 |$\times$| 3.4 pc|$^2$|⁠, and surrounds an X-ray Fe line source, G0.570|$-$|0.018. The mass and the kinetic energy of CO0.55|$+$|0.07 are estimated to be 10|$^{5.5}{M_\odot}$| and 10|$^{51.5}$|erg, respectively. The kinetic energy of SiO0.56|$-$|0.01 is |$\sim$|10|$^{50.4}$|erg. 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 |$\sim$|2 |$\times$| 10|$^{5}$|yr, which would suggest that it is a ‘bubble’ created by a massive stellar cluster, whose mass is estimated to be 10|$^{3.5{-}4.5}{M_\odot}$|⁠. 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.