\[ratecombo.fig\] is fairly mild in comparison to that of the QSOs.

Contamination of blind HI 21cm line surveys
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Figures. \[cosmcompare.fig\] and \[ratecombo.fig\] demonstrate that blind spectroscopic surveys are more likely to detect distant OH megamasers than HI from normal galaxies in the frequency bands below ${\sim}1200$MHz, assuming that both megamasers and normal galaxies have similar properties to those that are observed nearby. Above the rest frequency of the hydrogen line at $\nu_{HI} =$ 1420.4 MHz and in a small range of frequencies just below $\nu_{HI}$ there is a possibility for confusing OH emission at $z_{OH}\approx 1667/1420-1 = 0.17$ with weak HI signals from nearby dwarf galaxies and HI clouds. To explore this possibility in more detail, Fig. \[loZconfus.fig\] shows a a plot similar to Fig. \[ratecombo.fig\] with an expanded scale around 1420 MHz. The vertical axes have been adjusted to more convenient units to address this question. The possibility for confusion might arise in “blind surveys” for dwarf galaxies in the HI line, where signals at noise levels of a few $\sigma$ are selected as candidate dwarfs. At these sensitivity levels, only a narrow 1667 MHz might be detected, mimicing a narrow HI profile of a few 10’s of 