Channel maps of stacked Hnα n = 151–158 shown in color scale. Upper left panel: moment 0 image (velocity integrated emission;Fig. 2), with the positions and numbers of the spectra in Fig. 3 overlaid. The remaining panels show the RRL emission between −10 and 25 km s−1, with the corresponding contours of C¹⁸O emission (CHIMPS; Rigby et al. 2016; at levels of T_A = 0.65, 1.03,1.63, 2.59, 4.1 K) after binning to 5 km s−1 channels. The white dashed circles denote the shell of an expanding H II region (inner ring) and the assumed extent ofW49A (outer ring) as described in Fig. 1. The center of both radii is l = 43.1783°, b = − 0.0007°. Crosses denote stellar clusters identified in Alves & Homeier (2003). The angular resolution of the RRL emission is shown in the lower right corner of the left panel in the top row (orange). The angular resolution of the C ¹⁸ O emission is shown in the right panel of the bottom row, superposed as an empty hatched circle in gray on the RRL beam.