B-S and R-S HFSs in W49A. Left panels: heat map representing the hydrogen molecular column density overlaid with the integrated intensity contours of the R-S (bottom) and B-S (top) components of ¹²CO (3–2). The colored dots mark the skeletons of the filaments corresponding to the R-S (bottom) and B-S (top) components. Right panels: heat map representing the velocity distribution of the R-S (bottom) and B-S (top) components of ¹²CO (3–2), overlaid with contours of the integrated intensity of the R-S (bottom) and B-S (top) components. The masked area is where the integrated intensity is less than ten times that of the image rms. The red circle indicates the shell of the H II region in W49A-N with the radius of ~3.3 pc, and the black cross indicates the central location (Peng et al. 2010).