The HI of N891 (blue) detected in 20×12 hr of WSRT time (Oosterloo, Sancisi & Fraternali 2007, AJ, 134, 1019). A halo is detected out to 22 kpc vertically above the disk. Most of this halo is gas blown into the halo from the disk by star formation, but a small fraction is probably acretion of gas from the IGM. Such accretion is also needed to explain the lower rotation of the halo gas.


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