Incidence of HI 21-cm absorption in strong Fe II systems at 0.5 < z < 1.5

We present the results from our search for HI 21-cm absorption in a sample of 16 strong FeII systems [W-r(Mg II lambda 2796) >= 1.0 angstrom and W-r (FeII lambda 2600) or W-FeII >= 1 angstrom] at 0.5 < z < 1.5 using the Giant Metrewave Radio Telescope and the Green Bank Telescope. We report six new HI 21-cm absorption detections from our sample, which have increased the known number of detections in strong MgII systems at this redshift range by similar to 50 per cent. Combining our measurements with those in the literature, we find that the detection rate of HI 21-cm absorption increases with WFeII, being four times higher in systems with W-FeII >= 1 angstrom compared to systems with W-FeII < 1 angstrom. The N(HI) associated with the HI 21-cm absorbers would be >= 2 x 10(20) cm(-2), assuming a spin temperature of similar to 500 K (based on HI 21-cm absorption measurements of damped Lyman alpha systems at this redshift range) and unit covering factor. We find that HI 21-cm absorption arises on an average in systems with stronger metal absorption. We also find that quasars with HI 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 HI 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 HI 21-cm absorption detections at these redshifts is important to confirm various trends noted here with higher statistical significance.