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We present the results from our search for HI 21-cm absorption in a sample of16 strong FeII systems ($W_{\rm r}$(MgII $\lambda2796$) $\ge1.0$ \AA\ and$W_{\rm r}$(FeII $\lambda2600$) or $W_{\rm FeII}$ $\ge1$ \AA) at $0.5<z<1.5$using the Giant Metrewave Radio Telescope and the Green Bank Telescope. Wereport six new HI 21-cm absorption detections from our sample, which haveincreased the known number of detections in strong MgII systems at thisredshift range by $\sim50$%. Combining our measurements with those in theliterature, we find that the detection rate of HI 21-cm absorption increaseswith $W_{\rm FeII}$, being four times higher in systems with $W_{\rm FeII}$$\ge1$ \AA\ compared to systems with $W_{\rm FeII}$ $<1$ \AA. The $N$(HI)associated with the HI 21-cm absorbers would be $\ge 2 \times 10^{20}$cm$^{-2}$, assuming a spin temperature of $\sim500$ K (based on HI 21-cmabsorption measurements of damped Lyman-$\alpha$ systems at this redshiftrange) and unit covering factor. We find that HI 21-cm absorption arises on anaverage in systems with stronger metal absorption. We also find that quasarswith HI 21-cm absorption detected towards them have systematically higher$E(B-V)$ values than those which do not. Further, by comparing the velocitywidths of HI 21-cm absorption lines detected in absorption- and galaxy-selectedsamples, we find that they show an increasing trend (significant at$3.8\sigma$) with redshift at $z<3.5$, which could imply that the absorptionoriginates from more massive galaxy haloes at high-$z$. Increasing the numberof HI 21-cm absorption detections at these redshifts is important to confirmvarious trends noted here with higher statistical significance.

Incidence of HI 21-cm absorption in strong FeII systems at $0.5