2013A&A...550A.114B

We present long-slit integrated spectroscopy of 238 late-type galaxies belonging to the Herschel Reference Survey, a volume-limited sample representative of the nearby universe. This sample has a unique legacy value since it was ideally defined for any statistical study of the multifrequency properties of galaxies spanning a wide range in morphological type and luminosity. The spectroscopic observations cover the spectral range 3600-6900Å at a resolution R≃1000 and are thus suitable for separating both the underlying absorption from the emission of the Hβ line and the two [NII] lines from the Hα emission. We measured the fluxes and the equivalent widths of the strongest emission lines ([OII]λ3727, Hβ, [OIII]λ4959 and [OIII]λ5007, [NII]λ6548, Hα, [NII]λ6584, [SII]λ6717, and [SII]λ6731). We used the data to study the distribution of the equivalent width of all the emission lines, of the Balmer decrement C(Hβ), and of the observed underlying Balmer absorption under Hβ (EWHβ_abs) in this sample. Combining these new spectroscopic data with those available at other frequencies, we also study the dependence of C(Hβ) and EWHβ_abs on morphological type, stellar mass, stellar surface density, star formation rate, birthrate parameter, and metallicity in galaxies belonging to different environments (fields vs. Virgo cluster). The distribution of the equivalent width of all the emission lines, of C(Hβ) (or equivalently of A(Hα)), and of EWHβ_abs are systematically different in cluster and field galaxies. The Balmer decrement increases with the stellar mass, stellar surface density, metallicity, and star formation rate of the observed galaxies, while it is unexpectedly almost independent of the column density of the atomic and molecular gas. The dependence of C(Hβ) on stellar mass is steeper than previously found in other works. The underlying Balmer absorption does not significantly change with any of these physical parameters.