3 MILLIMETER MOLECULAR LINE OBSERVATIONS OF SAGITTARIUS B2 .2. HIGH-RESOLUTION STUDIES OF (CO)-O-18, HNCO, NH2CHO, AND HCOOCH3

High-resolution imaging of (CO)-O-18, HNCO, NH2CHO, and HCOOCH3 in Sgr B2 are presented in this study. The (CO)-O-18 emission comes mainly f rom the Sgr B2(M) and Sgr B2(N) dense cores and the western gas clump HNO(M). Toward Sgr B2(M), the (CO)-O-18 column density is 2 times high er and the fractional abundance is 80 times higher than toward Sgr B2( N). In HNO(M), the narrow line width implies that the (CO)-O-18 emissi on arises from the diffuse gas. The complex molecules NH2CHO and HCOOC H3 were detected only toward the Sgr B2(N) core. The HNCO K--1 = 2 emi ssion is detected only in Sgr B2(N) and is attributed to efficient rad iative pumping, which indicates the significant presence of far-infrar ed held and warm dust grains. Only similar to 4% of the HNCO was found in the K--1 = 0 ladders in Sgr B2(N). The nondetection of the K--1 = 2 emission toward Sgr B2(M) is caused by excitation and low abundance. In contrast, the HNCO K--1 = 0 emission comes mainly from the extende d gas component: the far northern region and HNCO(SW). For the K--1 = 0 transitions, T-rot = similar to 7 K. The low T-rot and the apparent ubiquity of HNCO suggest that abundant HNCO exists in the Sgr B2 envel ope. The HNCO K--1 = 0 emission unveiled two spatially extended veloci ty components; the velocity gap between them covers the same LSR veloc ities of the Sgr B2 dense cores. If HNCO is formed via surface reactio ns, the pervasive detection of HNCO in the outer edges of Sgr B2 cloud core leads to the cloud-cloud collision postulate. A north-south (CO) -O-18 bipolar structure was seen in Sgr B2(M) centered at the compact H II region F. The bipolar structure appears asymmetric and thus favor s the outflow interpretation. The sharp outer edges of the (CO)-O-18 l ine profiles of the two lobes further support the outflow picture. The estimated outflow age is similar to 2 +/- 1 x 10(4) yr, and the total mass is similar to 1700 M(.). The outflow masses for the blue and red lobes are less than or equal to 360 M(.) and less than or equal to 41 0 M(.), respectively. The mass-loss rate is thus less than or equal to 0.037 M(.) yr(-1). The detection of outflows in Sgr B2(M) supports th e gas dispersal picture and subsequent chemical variations disclosed b y the HNO and (HCCCN)-C-13 emission void. Three distinct velocity comp onents toward Sgr B2(N) were seen from the HNCO K--1 = 2 emission. The broad component is centered at the H II region K2 with a north-south velocity gradient, which is probably due to rotation. The mass of the rotating cloud is between similar to 630 and 1570 M(.). The two narrow components are located on the opposite sides of the K1-K2 ridge and a re in fact the two lobes of a gas outflow. The estimated outflow age o f Sgr B2(N) is similar to 6 x 10(3) yr, which is a factor of 3 younger than Sgr B2(M). The outflow masses are less than or equal to 200 and less than or equal to 300 -1 M(.) for the red and blue lobes, respecti vely. This yields a mass-loss rate less than or equal to 0.08 M(.) yr( -1), about 2 times higher than that of Sgr B2(M). All these suggest th at Sgr B2(N) is much younger than Sgr B2(M). Finally, high-resolution imaging of the radiatively excited HNCO K--1 = 2 transition allows the separation of an apparent bipolar structure into a gas outflow and a rotating disk cloud.