... Animation of the neutral hydrogen data cube from Westerbork. ... VIRGOHI 21 was a dark galaxy candidate discovered in 2005 it was found to contain no starlight down to a very low surface-brightness level, yet its velocity structure implied that it had a mass of 10 10 10 11 solar masses. ... VIRGOHI 21 was first observed in the 21-cm line of neutral hydrogen with the Lovell telescope at Jodrell Bank Observatory and the detection was confirmed using the Arecibo telescope ( Davies et al. ...

... 2.3 Data acquisition Spectra generated by the Multibeam correlator contain the usual structure seen in spectra from other H i instruments: a bandpass spectrum which is the sum of the sky , ground and receiver temperatures multiplied by the product of the filters in the receiver chain; superimposed on this is a noise ... Note also that sources extended much beyond ,40 arcmin can be imaged poorly in HIPASS images because of the bandpass sidelobe effect described in Section 3.3. ...