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Despite powerful X-ray emission, some AGNs are known to either lack opticalemission lines (so-called 'optically dull' AGNs) or have lines that fall on thestar-forming branch of the BPT diagram ('misclassified' AGNs). Aperture effectshave been proposed to explain such atypical spectra, especially when based onSDSS (3'') fibers. We use observations from VLT-MUSE with Adaptive Optics toexplore the spatially resolved optical emission line properties of 4 opticallydull and 1 misclassified X-ray AGN candidates. VLT-MUSE IFU spectra allow us toinvestigate the extent to which the aperture size affects the emission linemeasurements. The optically dull AGNs become detectable in deeper VLT-MUSEspectroscopic apertures having the same size (3'') as SDSS fibers, suggestingno AGN is truly lineless. However, in no case does the line become moredetectable as the aperture decreases, as would be expected if dilution bystrong continuum was responsible for making the lines appear weak. We also showthat the misclassified X-ray AGN retains the same position on the BPT diagramin smaller apertures (down to 0.''5), demonstrating that its misclassificationis not the result of the dilution by HII regions. Thus, we conclude thatcontinuum swamping or star formation dilution, i.e., aperture effects, are notresponsible for atypical lines. Rather, the AGN lines are intrinsically weak.

VLT-MUSE spectroscopy of AGNs misclassified by BPT diagnostic or with weak emission lines