We present the results from our search for H i 21-cm absorption in a sample of 16 strong Fe ii systems ( W _ { r } ( Mg ii \lambda 2796 ) \geq 1.0 Å and W _ { r } ( Fe ii \lambda 2600 ) or W _ { \mbox { Fe { \sc ii } } } \geq 1 Å ) at 0.5 < z < 1.5 using the Giant Metrewave Radio Telescope and the Green Bank Telescope .
We report six new H i 21-cm absorption detections from our sample , which have increased the known number of detections in strong Mg ii systems at this redshift range by \sim 50 % .
Combining our measurements with those in the literature , we find that the detection rate of H i 21-cm absorption increases with W _ { \mbox { Fe { \sc ii } } } , being four times higher in systems with W _ { \mbox { Fe { \sc ii } } } \geq 1 Å compared to systems with W _ { \mbox { Fe { \sc ii } } } < 1 Å .
The N ( H i ) associated with the H i 21-cm absorbers would be \geq 2 \times 10 ^ { 20 } cm ^ { -2 } , assuming a spin temperature of \sim 500 K ( based on H i 21-cm absorption measurements of damped Lyman- \alpha systems at this redshift range ) and unit covering factor .
We find that H i 21-cm absorption arises on an average in systems with stronger metal absorption .
We also find that quasars with H i 21-cm absorption detected towards them have systematically higher E ( B - V ) values than those which do not .
Further , by comparing the velocity widths of H i 21-cm absorption lines detected in absorption- and galaxy-selected samples , we find that they show an increasing trend ( significant at 3.8 \sigma ) with redshift at z < 3.5 , which could imply that the absorption originates from more massive galaxy haloes at high- z .
Increasing the number of H i 21-cm absorption detections at these redshifts is important to confirm various trends noted here with higher statistical significance .