A treatment procedure for Gemini North / NIFS data cubes : application to NGC 4151

We present a detailed procedure for treating data cubes obtained with the Near-Infrared Integral Field Spectrograph (NIFS) of the Gemini North telescope. This process includes the following steps: correction of the differential atmospheric refraction, spatial re-sampling, Butterworth spatial filtering, ‘instrumental fingerprint’ removal and Richardson–Lucy deconvolution. The clearer contours of the structures obtained with the spatial re-sampling, the high spatialfrequency noise removed with the Butterworth spatial filtering, the removed ‘instrumental fingerprints’ (which take the form of vertical stripes along the images) and the improvement of the spatial resolution obtained with the Richardson–Lucy deconvolution result in images with a considerably higher quality. An image of the Brγ emission line from the treated data cube of NGC 4151 allows the detection of individual ionized-gas clouds (almost undetectable without the treatment procedure) of the narrow-line region of this galaxy, which are also seen in an [O III] image obtained with the Hubble Space Telescope. The radial velocities determined for each one of these clouds seem to be compatible with models of biconical outflows proposed by previous studies. Considering the observed improvements, we believe that the procedure we describe in this work may result in more reliable analysis of data obtained with this instrument.