Upper panel: image of the 3D-HST bi-dimensional spectrum for source 4491 (ID-MUSIC), as displayed by the IDL routine. The red horizontal lines define the “virtual slit”. Lower panel: 1D spectrum of source 4491, obtained by collapsing the 2D spectrum along the columns inside the virtual slit. The flux is in erg/s/cm²/Å. The black thicker histogram indicates the observed spectrum, and the red curve is a spline interpolation to the observed spectrum. The gray thin histogram, almost overlapping the black one, represents the “decontaminated spectrum”, i.e., the contamination model by Brammer et al. (2012) subtracted to the observed spectrum. The overlap between the observed and the decontaminated spectra highlights the negligible contamination flux in the region defined by the virtual slit. The vertical blue line highlights the position of the Hα emission while the pale blue lines correspond to the position of the [NII] doublet.