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Context. The determination of the relative frequency of active galacticnuclei (AGN) versus other spectral classes, for example, HII region-like (HII),transition objects (TRAN), passive (PAS), and retired (RET), in a complete setof galaxies in the local Universe is of primary importance to discriminate thesource of ionization in the nuclear region of galaxies. Aims. Here we aim toprovide a spectroscopic characterization of the nuclei of galaxies belonging tothe Herschel Reference Survey (HRS), a volume and magnitude limited samplerepresentative of the local Universe, which has become a benchmark for localand high-z studies, for semianalytical models and cosmological simulations. Thecomparison between the nuclear spectral classification and the one determinedon the global galactic scale provides information about how galaxy propertieschange from the nuclear to the outer regions. Moreover, the extrapolation ofthe global star formation (SF) properties from the SDSS fiber spectroscopycompared to the one computed by Halpha photometry can be useful for testing themethod based on aperture correction for determining the global star formationrate (SFR) for local galaxies. Methods. By collecting the existing nuclearspectroscopy available from the literature, complemented with new observationsobtained using the Loiano 1.52m telescope, we analyze the 322 nuclear spectraof HRS galaxies. Results. Using two diagnostic diagrams (the BPT and the WHAN)we provide a nuclear and an integrated spectral classification for the HRSgalaxies. Conclusions. We find that the fraction of AGNs increases with stellarmass, such that at logM > 10.0 M\odot or 66% of the LTGs are AGNs or TRAN.

Nuclear vs. Integrated Spectroscopy of Galaxies in the Herschel Reference Survey