HNCO in massive galactic dense cores

We surveyed 81 dense molecular cores associated with regions of massive sta r formation and Sgr A in the J(K-1K1) = 5(05) - 4(04) and 10(010) - 9(09) l ines of HNCO. Line emission was detected towards 57 objects. Selected subsa mples were also observed in the lot - 0(00), 4(04) - 3(03), 7(07) - 6(06), 15(015) - 14(014), 16(016) - 15(015) and 21(021) - 20(020) lines, covering a frequency range from 22 to 461 GHz. HNCO lines from the K-1 = 2, 3 ladder s were detected in several sources. Towards Orion-KL, K-1 = 5 transitions w ith upper state energies E-u/k similar to 1100 and 1300 K could be observed . Five HNCO cores were mapped. The sources remain spatially unresolved at 220 and 461 GHz (10(010) - 9(09) and 21(010) 20(020) transitions) with beam si zes of 24 " and 18 ", respectively. The detection of hyperfine structure in the 1(01) - 0(00) transition is consistent with optically thin emission un der conditions of Local Thermodynamic Equilibrium (LTE). This is corroborat ed by a rotational diagram analysis of Orion-KL that indicates optically th in line emission also for transitions between higher excited states. At the same time a tentative detection of interstellar (HNCO)-C-13 (the 10(0,10) - 9(0,9) line at 220 GHz toward G 310.12-0.20) suggests optically thick emi ssion from some rotational transitions. Typical HNCO abundances relative to Hz as derived from a population diagram analysis are similar to 10(-9). The rotational temperatures reach similar to 500 K The gas densities in regions of HNCO K-1 = 0 emission should be n greater than or similar to 10(6) cm(-3) and in regions of K-1 > 0 emission about an order of magnitude higher even for radiative excitation. HNCO abundances are found to be enhanced in high-velocity gas. KNCO integra ted line intensities correlate well with those of thermal SiO emission. Thi s indicates a spatial coexistence of the two species and may hint at a comm on production mechanism, presumably based on shock chemistry.