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Distribution of HNCO 505−404 in massive star-forming regions

Aims. The goal of this paper is to study the spatial distribution of HNCO in massive star-forming regions, and investigate its spatial association with infrared sources, as well as physical conditions in region of HNCO emission. Methods. We have mapped nine massive star-forming regions in HNCO 505-404 with the Purple Mountain Observatory 13.7m telescope. The C 18 O maps of these sources were obtained simultaneously. Results. The HNCO emission shows compact distribution, with emission peak centred on water masers. Nearly all the HNCO clumps show signs of embedded mid-infrared or far-infrared sources. The FWHM sizes of HNCO clumps are significantly smaller than C 18 O clumps but rather similar to HC3N clumps. We also found good correlation between the integrated intensities, linewidths and LSR velocities of HNCO and HC3N emission, implying similar excitation mechanism of these two species. As such, collisional excitation is likely to be the dominant excitation mechanism for HNCO 505 404 emission in galactic massive star-forming regions.