Continuum maps at 242 GHz (Sánchez-Monge et al. 2017) shown in colour scale and at 99.2 GHz (ReMoCA) shown with teal contours. The contour steps start at 3σ and then increase by a factor of 2 with σ = 0.4 K the rms noise level of the continuum map at 99.2 GHz. The black cross shows the phase centre of the ReMoCA observations. The white cross shows the intensity-weighted 3 mm continuum peak determined in this work. Orange crosses indicate 1.3 mm continuum sources from Sánchez-Monge et al. (2017), cyan crosses the continuum peaks of the hot cores N1 and N2 as well as the line density peak of N3 reported by Bonfand et al. (2017) on the basis of the EMoCA survey at 1.6″ resolution, and pink crosses HII regions reported by Gaume et al. (1995) (K1-K6, K9.69) and De Pree et al. (2015) (K7) with the VLA. The black box indicates the region for which spectral indices are determined as shown in Fig. 2. The respective synthesised beams for both maps are shown in the lower right corner.