We report the detection of 21-cm absorption at z _ { abs } = 0.656 towards 1622+238 ( 3C 336 ) .
The line is very broad with a Full-Width Half Maximum ( FWHM ) of 235 { km s } ^ { -1 } , giving a velocity integrated optical depth of \int \tau dv = 2.2 \pm 0.2 { km s } ^ { -1 } .
The centroid of the line is offset from that of the known damped Lyman- \alpha absorption ( DLA ) system by 50 { km s } ^ { -1 } , and if the Lyman- \alpha and 21-cm absorption are due to the same gas , we derive a spin temperature of T _ { s } \leq 60 K , which would be the lowest yet in a DLA .
The wide profile , which is over four times wider than that of any other DLA , supports the hypothesis that the hydrogen absorption is occurring either in the disk of a large underluminous spiral or a group of dim unidentified galaxies , associated with the single object which has been optically identified at this redshift .