We present sensitive Giant Metrewave Radio Telescope ( GMRT ) and high-resolution Arecibo HI 21-cm observations of the damped Lyman- \alpha absorber ( DLA ) at z = 0.2212 towards OI 363 ( B 2 ~ { } 0738 + 313 ) .
The GMRT and Arecibo spectra are in excellent agreement and yield a spin temperature T _ { s } = 890 \pm 160 K , consistent with earlier lower sensitivity observations of the system .
This value of T _ { s } is far higher than spin temperatures measured for the Milky Way and local spirals but is similar to T _ { s } values obtained in the majority of damped absorbers ( T _ { s } \ga 1000 K ) . The high velocity resolution of the Arecibo spectra enables us to obtain estimates of physical conditions in the absorbing clouds by fitting multiple Gaussians to the absorption profile .
The spectra are well fit by a three-component model with two narrow and one wide components , with temperatures { T _ { k _ { 1 } } } = 308 \pm 24 K , { T _ { k _ { 2 } } } = 180 \pm 30 K and { T _ { k _ { 3 } } } = 7600 \pm 1250 K , respectively .
The last of these is in excellent agreement with the expected temperatures for the WNM ( 5000 - 8000 K ) .
Further , the mere fact that components are seen with lower temperatures than the estimated T _ { s } implies that the absorber must have a multi-phase medium . We use the measured 21-cm optical depth and the above estimates of the kinetic temperature to obtain the HI column density in the various components .
The total column density in the narrow components is found to be N _ { HI } ( { CNM } ) \leq 1.9 \pm 0.25 \times 10 ^ { 20 } cm ^ { -2 } , while that in the wide component is N _ { HI } ( { WNM } ) \geq 1.26 \pm 0.49 \times 10 ^ { 21 } cm ^ { -2 } .
Thus , the WNM contains at least 75 % of the total HI in the z = 0.2212 DLA , unlike our Galaxy , in which the CNM and WNM have equitable contributions .
As conjectured earlier ( Chengalur & Kanekar 2000 ) , this accounts for the difference in the spin temperatures of the z = 0.2212 system and local spirals , suggesting that the DLA is probably a dwarf or LSB type galaxy ; this is also in agreement with optical studies ( Turnshek et al .
2001 ) .
Finally , the total column density in the DLA is found to be N _ { HI } \sim 1.45 \pm 0.49 \times 10 ^ { 21 } cm ^ { -2 } , which agrees within the errors with the value of N _ { HI } = 7.9 \pm 1.4 \times 10 ^ { 20 } cm ^ { -2 } , obtained from the Lyman- \alpha profile ( Rao & Turnshek 1998 ) .
This reinforces our identification of the wide and narrow components as the WNM and CNM respectively .