An unusual molecular cloud complex in the Galactic Centre

A high-velocity molecular cloud complex at |$l \sim 5^\circ_. 4, \enspace b \sim -0^\circ_. 4$|⁠, having an anomalously wide velocity width of ∼ 220 km s−1 has been mapped in the absorption line of formaldehyde at a 6-cm wavelength, using the Jodrell Bank Mk II Radio Telescope (beamwidth 8.8×9.9 arcmin2). The spectra are presented, along with a map of integrated absorption and contour maps showing line temperature as a function of latitude and velocity (b–V maps). The total molecular mass of the complex is estimated to be |$\sim 5 \times 10^6\enspace M_\odot$|⁠. Most of this mass is seen in 11 discrete clouds with average mass |$\sim 5 \times 10^5\enspace M_\odot$|⁠, average linewidth ∼ 15 km s−1 and average size ∼ 18 pc. These clouds appear bound against galactic tidal forces and lie close to virial equilibrium. The gas distribution covers a very large velocity range and shows a systematic variation of velocity with latitude and longitude. The complex is symmetrically placed about the centre with respect to the ‘Clump 1’ feature studied by Bania and has a similar non-circular velocity. The possibility that the complex is part of a coherent structure such as a dust lane or inner spiral arm is discussed. The interpretation of the unusually broad linewidths is also discussed.