A press release was made for this poster. HI self-absorption (HISA) against background HI 21cm emission reveals cold atomic gas structures in the interstellar medium. ... 1999; English et al. ... Our investigation has uncovered a wealth of remarkable features in both the Local and Perseus Arms. ... Here T_on and T_off are continuum-subtracted ON and OFF brightnesses, and p is the fraction of T_off emission lying behind the HISA feature. Constraining p leaves two unknowns, tau_hisa and T_spin . ...

... 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. ...