The DIVING Survey – Deep IFS View of Nuclei of Galaxies – III. Analysis of the nuclear region of the early-type galaxies of the sample

We analysed the nuclear region of all 56 early-type galaxies from the DIVING Project, which is a statistically complete sample of objects that contains all 170 galaxies in the Southern Hemisphere with B < 12.0 mag and galactic latitude |b| < 15. Observations were performed with the Integral Field Unit of the Gemini Multi-Object Spectrograph. Emission lines were detected in the nucleus of 86 ± 5 per cent of the objects. Diagnostic diagrams were used to classify 52 ± 7 per cent of the objects as LINERs or Seyferts, while the other 34 ± 6 per cent galaxies without H β or [O III] lines in their spectra were classified as weak emission line objects. Transition Objects are not seen in the sample, possibly because the seeing-limited data cubes of the objects allow one to isolate the nuclei of the galaxies from their circumnuclear regions, avoiding contamination from H II regions. A broad line region is seen in 29 ± 6 per cent of the galaxies. Of the 48 galaxies with emission-line nuclei, 41 have signs of AGNs. Some objects also have indications of shocks in their nuclei. Lenticular galaxies are more likely to have emission lines than ellipticals. Also, more luminous objects have higher [N II]/H α ratios, which may be associated with the mass-metalicity relation of galaxies. A direct comparison of our results with the Palomar Survey indicates that the detection rates of emission lines and also of type 1 AGNs are higher in the DIVING objects. This is a consequence of using a more modern instrument with a better spatial resolution than the Palomar Survey observations.