A survey for HI in voids

We have searched for HI in some nearby voids using the Dwingeloo radio telescope. It appears that a sufficient part of the frequency band is free from radar interference to allow such studies, especially of the Perseus void. A search covering a small fraction of this void was sensitive (at the 10 σ level) to about 3.1010 h-2 M solar mass. No signals at this level were found except for a possible but very weak one in the direction of UGC 749. It is concluded that the Dwingeloo telescope is sufficiently stable and sensitive to detect any cosmologically significant amount of HI in the Perseus void