¹²CO (1−0) moment 0 map and average spectra of sixteen sub-regions for the W3/4 region. (a) ¹²CO (1−0) moment 0 (velocity integrated intensity) map of the W3/4 region. The integrated Local Standard of Rest velocity range is −63 to −30 km s⁻¹. The black contour line is the ¹³CO intensity in the integrated Local Standard of Rest velocity range from −63 to −28 km s⁻¹, starting at 10 K km s⁻¹ (3σ) on a main beam brightness temperature scale and going up in steps of 15 K km s⁻¹. The red areas refer to positions with notable C¹⁸O emission. Sixteen dotted boxes mark the dense areas in the whole W3/4 region. The yellow stars and red crosses correspond to OB stars (Roman-Lopes et al. 2019) and high-mass young stellar objects (HMYSOs) (Lumsden et al. 2013), respectively. (b) Average spectra of the sixteen sub-regions for the ¹²CO (black), ¹³CO (blue) and C¹⁸O (red) J = 1−0 emission lines. The yellow dotted line in each sub-region marks the velocity value corresponding to the peak of the ¹²CO average spectrum. The upper left corner of each sub-map shows the corresponding sub-region given in (a).