HB8903: a) white contours show the continuum emission from HB8903 at 3 mm with a beam of 0.62′′×0.46′′ (the synthesised beam is shown in the bottom-left corner). Contours are at the level of 25, 50, 100 and 200 times the noise per beam (18 μJy). The colour background image shows the continuum emission in H-band from SINFONI data of HB8903. b) ALMA spectrum extracted from an aperture as large as the beam size and rebinned to 120 km s^-1. The vertical dashed and solid green line mark the expected positions for CO(3−2) emission line at the redshifted of the narrow Hα and [Oiii]λ5007 component, respectively (Carniani et al. 2016): the line is not detected. c) CO(3−2) map obtained by integrating the cube under the two vertical dotted line indicated in the panel b (i.e. − 200 km s^-1<v< 200 km s^-1). Negative and positive contours are in steps of 1σ, which is 0.027 Jy/beam km s^-1. The synthesised beam is shown in the bottom-left corner.