Observations of the 1 _ { 10 } -1 _ { 01 } 556.936 GHz transition of ortho-water with the Submillimeter Wave Astronomy Satellite ( SWAS ) have revealed the presence of widespread emission and absorption by water vapor around the strong submillimeter continuum source Sagittarius B2 .
An incompletely-sampled spectral line map of a region of size 26 \times 19 arcmin around Sgr B2 reveals three noteworthy features .
First , absorption by foreground water vapor is detectable at local standard-of-rest ( LSR ) velocities in the range –100 to 0 km/s at almost every observed position .
Second , spatially-extended emission by water is detectable at LSR velocities in the range 80 to 120 km/s at almost every observed position .
This emission is attributable to the 180-pc molecular ring identified from previous observations of CO .
The typical peak antenna temperature of 0.075 K for this component implies a typical water abundance of 1.2 – 8 \times 10 ^ { -6 } relative to H _ { 2 } .
Third , strong absorption by water is observed within 5 arcmin of Sgr B2 at LSR velocities in the range 60 to 82 km/s .
An analysis of this absorption yields a H _ { 2 } ^ { 16 } O abundance \sim 2 - 4 \times 10 ^ { -7 } relative to H _ { 2 } if the absorbing water vapor is located within the core of Sgr B2 itself ; or , alternatively , a water column density of \sim 2.5 - 4 \times 10 ^ { 16 } cm ^ { -2 } if the water absorption originates in the warm , foreground layer of gas proposed previously as the origin of ammonia absorption observed toward Sgr B2 .