Using the Effelsberg 100-m telescope , absorption in the ( J , K ) = ( 1,1 ) , ( 2,2 ) and ( 3,3 ) inversion lines of ammonia ( NH _ { 3 } ) was detected at a redshift of z = 0.6847 toward the gravitational lens system B0218+357 .
The \lambda \sim 2 cm absorption peaks at 0.5–1.0 % of the continuum level and appears to cover a smaller fraction of the radio continuum background than lines at millimeter wavelengths .
Measured intensities are consistent with a rotation temperature of \sim 35 K , corresponding to a kinetic temperature of \sim 55 K. The column density toward the core of image A then becomes N ( NH _ { 3 } ) \sim 1 \times 10 ^ { 14 } cm ^ { -2 } and fractional abundance and gas density are of order X ( NH _ { 3 } ) \sim 10 ^ { -8 } and n ( H _ { 2 } ) \sim 5 \times 10 ^ { 3 } cm ^ { -3 } , respectively .
Upper limits are reported for the ( 2,1 ) and ( 4,4 ) lines of NH _ { 3 } and for transitions of the SO , DCN , OCS , SiO , C _ { 3 } N , H _ { 2 } CO , SiC _ { 2 } , HC _ { 3 } N , HC _ { 5 } N , and CH _ { 3 } OH molecules .
These limits and the kinetic temperature indicate that the absorption lines are not arising from a cold dark cloud but from a warm , diffuse , predominantly molecular medium .
The physical parameters of the absorbing molecular complex , seen at a projected distance of \sim 2 kpc to the center of the lensing galaxy , are quite peculiar when compared with the properties of clouds in the Galaxy or in nearby extragalactic systems .