The interaction of the Galactic center filament system G359.54+0.18 with its ambient medium

We present a multi-wavelength study of the Galactic center filament system G359.54+0.18 and potentially associated, nearby molecular clouds. The data include, (1) 3 mm multi-line observations of CS, HCO+, and other molecular species, (2) observations of low-J transitions of 12CO and 13CO, (3) 5 GHz radio interferometric continuum emission observations and (4) H79α recombination line observations. The high-sensitivity VLA images reveal continuum emission with a clumpy morphology towards the eastern tip of the nonthermal filaments. The transition from filamentary to clumpy structure appears to be continuous, implying association between the two. A dense molecular cloud is situated adjacent to the eastern border of the clumped continuum emission region. The cloud is part of the negative velocity feature, an elongated complex of Galactic center molecular clouds distinguished by its coherent kinematic structure across about a degree in longitude. A 3σ detection of H79α recombination line emission indicates that the extended continuum component is thermal in nature and links it kinematically to the molecular gas. A steep velocity gradient in the molecular cloud towards the interface to the HII region and the excitation conditions of the gas derived from our multiline survey also imply interaction between the molecular cloud and the HII region. Higher angular resolution data confirm the association between the filaments and a second molecular cloud at a position where the nonthermal filaments are bent, as was previously suggested by Bally & Yusef-Zadeh (1989). The morphological and kinematic evidence for the interaction of the G359.54+0.18 nonthermal filaments with an HII region and molecular clouds makes G359.54+ 0.18 the fourth association of this kind observed in the Galactic center region.