2022ApJ...928...83Y

Using archival infrared data of GLIMPSE, Hi-GAL, and molecular line data of SEDIGISM, MSGPCOS, and MALT90, we investigate the physical and chemical properties of the molecular gas associated with the mid-infrared bubble S156. By the method of spectral energy distribution, we made H₂ column density and dust temperature maps of this region. We find two clouds with masses of 5.4 ± 1.1 x 10⁴M_☉ and 2.2 ± 0.5 x 10⁴M_☉, respectively. In both of the two clouds, the ¹³CO (2-1/1-0) and ¹³CO (2-1)/N₂H⁺ (1-0) intensity ratios are enhanced on the boundary. Cloud A has a clear dust temperature gradient decreasing from the boundary to the outside region. Our analysis indicates cloud A is mainly influenced by the feedback from S156, while cloud B is affected both by S156 and the G305 complex. We also find the ¹³CO and C₂H emissions tend to be brighter in photon dominated regions (PDRs), while N₂H⁺ is brighter in the regions of cold gas that is far away. Furthermore, we make the abundance maps of C₂H and N₂H⁺ of cloud A. We find the abundance of C₂H is enhanced in the region facing ionizing stars and it decreases steadily moving away from them. On the other hand, the abundance of N₂H⁺ increases from the ionized boundary to the cold gas outward. These phenomena indicate C₂H prefers to be produced in hot gas such as PDRs, while N₂H⁺ could be destroyed by it. Our study also suggests the abundance ratio of C₂H to N₂H⁺ could trace PDRs in the late stages of massive star formation.