The infrared deep sample (IDS), in the north ecliptical polar region (NEPR), is the first complete, far--IR selected sample, on which numerous studies of galaxy evolution are based. Here we present and analyze the spectral classification of several galaxies in the IDS sample together with rotation curves which allow estimating the lower mass limits of a subsample of objects. We measured fluxes and intensity ratios of the emission lines in the visible region of the spectrum (lambda 4000-9000 A) for 75 galaxy members. Moreover, for some of them (55%), the spectra obtained with the Keck II telescope have sufficient wavelength and spatial resolution to derive their rotation curve. These galaxies turn out to be disk like systems, with a high fraction (~50%) of interacting systems. The spectroscopic classification of 42 galaxies, using the emission-line ratio diagnostic diagrams, shows that the NEPR sample is predominantly composed of starburst galaxies (71%), while the fraction of AGNs (7%) and LINERs (21%) is small. The dynamical analysis allows us to estimate the lower mass limits of 39 galaxies. The rest-frame FIR luminosity distribution of these galaxies spans the same range as that of the FIR selected complete sample, i.e. three orders of magnitude, with the same mean value, log(L_FIR)=10.2. This emphasizes that such galaxies represent FIR properties of the whole sample well. Moreover, their optical properties are typical of the sample itself since 62% of these belong to the 60mu selected complete sample.
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