The Motions of Formaldehyde Clouds Near Sgr A

It is well known that a molecular cloud complex with a radial velocity of 40 km s^-1 is located in front of and near Sgr A, the non-thermal source at the centre of our galaxy. The motion of this cloud is generally interpreted as a contraction towards the centre. In terms of the general kinematics of our galaxy the existence of contraction is not firmly established - the main spiral features are either stationary with respect to the local standard of rest or expanding outwards from the centre (e.g., the 4 kpc expanding arm). However, as a result of a high-resolution study of the H₂CO absorption arising in the molecular cloud, an alternative interpretation not involving contraction is suggested.