In order to study a molecular-cloud-scale chemical composition , we have conducted a mapping spectral line survey toward the Galactic molecular cloud W3 ( OH ) , which is one of the most active star forming regions in the Perseus arm , with the NRO 45 m telescope .
We have observed the area of 16 ^ { \prime } \times 16 ^ { \prime } , which corresponds to 9.0 pc \times 9.0 pc .
The observed frequency ranges are 87 - 91 , 96 - 103 , and 108 - 112 GHz .
We have prepared the spectrum averaged over the observed area , in which 8 molecular species CCH , HCN , HCO ^ { + } , HNC , CS , SO , C ^ { 18 } O , and ^ { 13 } CO are identified .
On the other hand , the spectrum of the W3 ( OH ) hot core observed at a 0.17 pc resolution shows the lines of various molecules such as OCS , H _ { 2 } CS CH _ { 3 } CCH , and CH _ { 3 } CN , in addition to the above species .
In the spatially averaged spectrum , emission of the species concentrated just around the star-forming core such as CH _ { 3 } OH and HC _ { 3 } N is fainter than in the hot core spectrum , whereas emission of the species widely extended over the cloud such as CCH is relatively brighter .
We have classified the observed area into 5 subregions according to the integrated intensity of ^ { 13 } CO , and have evaluated the contribution to the averaged spectrum from each subregion .
The CCH , HCN , HCO ^ { + } , and CS lines can be seen even in the spectrum of the subregion with the lowest ^ { 13 } CO integrated intensity range ( < 10 K km s ^ { -1 } ) .
Thus , the contributions of the spatially extended emission is confirmed to be dominant in the spatially averaged spectrum .