PAH intensity ratio, |$I_{\rm {PAH}}/I_{\rm {TIR}}$|⁠, and the emissivity power-law index of the cold dust component, |$\beta _{\rm {c}}$|⁠, maps of the IR bubbles that have bridge features in the CO position–velocity maps. The left-hand panels show the AKARI 9 |$\mu$|m and 18 |$\mu$|m band images in green and red, respectively. The cyan circles in the left-hand panels correspond to the peak positions of the hot dust emissions. The white squares correspond to the regions where the bridge features had been observed (N18; Torii et al. 2020, N35; Torii et al. 2018, N37; Baug et al. 2016, N49; Dewangan et al. 2017, S7; Torii et al. 2015, S44; Kohno et al. 2020). The white crosses in the right-hand panels correspond to the positions of massive clumps identified by Csengeri et al. (2014). (Color online)