Central Panel: positions of our analysis in W44E (W44E1: black circle, W44E2: blue circle) on the velocity-integrated CO (6–5) emission ( integrated between 0 km s^-1 and 90 km s^-1) convolved to the CO (3–2) angular resolution of 18 (colour background) with half-maximum contour in black. The wedge unit is K km s^-1. The blue and black circles indicate the APEX beam size of our observations in CO (3–2). The APEX beam sizes of our CO (3–2), CO (4–3), CO (6–5), and CO (7–6) observations are also provided (upper left corner, see also Table 1). The black and light blue hexagons mark the position of the OH masers observed by Claussen et al. (1997) and Hoffman et al. (2005). Left Panel: spectra observed in the position W44E1 (in T_MB), CO (3–2), black; CO (4–3), pink; CO (6–5), dark blue; CO (7–6), light blue; ¹³CO (3–2), green. The CO spectral resolution is 1.0 km s^-1 for all lines. Right panel: spectra observed in the position W44E2, same colours as in the left panel.