... Molecular clouds are enmeshed in webs of diffuse atomic gas that contain important information about their formation and interaction with their environment, not least because the atomic gas can trace lower column densities that are unshielded from UV radiation. ... The GALFA H I sky survey of Galactic 21cm-line emission with the Arecibo L-band Feed Array has recently mapped the MBM 53-55 region with a 3.5-arcminute beam and 0.2 km/s channels. ... Other GALFA publications ...

... 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. ...