We present a simple metallicity estimator based on the logarithmic [N ii] λ6584/Hα ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey‐quality data even for moderately low spectral resolution. We have calibrated the N2 estimator using a compilation of H ii galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities. The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from approximately 1/50th to twice the Solar value [7.2<12+log(O/H)<9.1]. We suggest that the ([S ii] λλ6717,6731/Hα) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [N ii] λ6584 is not detected or in low‐resolution spectra where [N ii] λ6584 is blended with Hα.

We have derived ages, metallicities and enhanced‐element ratios [α/Fe] for a sample of 83 early‐type galaxies essentially in groups, the field or isolated objects. The stellar‐population properties derived for each galaxy correspond to the nuclear re/8 aperture extraction. The median age found for Es is 5.8±0.6 Gyr and the average metallicity is +0.37±0.03 dex. For S0s, the median age is 3.0±0.6 Gyr and [Z/H]= 0.53±0.04 dex. We compare the distribution of our galaxies in the Hβ‐[MgFe] diagram with Fornax galaxies. Our elliptical galaxies are 3–4 Gyr younger than Es in the Fornax cluster. We find that the galaxies lie in a plane defined by [Z/H]= 0.99 log σ0− 0.46 log(age) − 1.60, or in linear terms Z ∝σ0× (age) −0.5. More massive (larger σ0) and older galaxies present, on average, large [α/Fe] values, and therefore must have undergone shorter star‐formation time‐scales. Comparing group against field/isolated galaxies, it is not clear that environment plays an important role in determining their stellar‐population history. In particular, our isolated galaxies show ages differing by more than 8 Gyr. Finally we explore our large spectral coverage to derive log (O/H) metallicity from the Hα and N iiλ6584 and compare it with model‐dependent [Z/H]. We find that the O/H abundances are similar for all galaxies, and we can interpret it as if most chemical evolution has already finished in these galaxies.

This is the first paper of a series on the investigation of stellar population properties and galaxy evolution of an observationally homogeneous sample of early-type galaxies in groups, field and isolated galaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopy of 86 nearby elliptical and S0 galaxies. Eight of them are isolated, selected according to a rigorous criterion, which guarantees a genuine low-density subsample. The present survey has the advantage of covering a larger wavelength range than normally found in the literature, which includes [O III] λ5007 and Hα, both lines important for emission correction. Among the 86 galaxies with S/N 15 (per resolution element, for r e /8 central aperture), 57 have their Hβ-index corrected for emission (the average correction is 0.190 Å in Hβ) and 42 galaxies reveal [O III] λ5007 emission, of which 16 also show obvious Hα emission. Most of the galaxies in the sample do not show obvious signs of disturbances nor tidal features in the morphologies, although 11 belong to the Arp catalogue of peculiar galaxies; only three of them (NGC 750, 751 and 3226) seem to be strongly interacting. We present the measurement of 25 central line-strength indices calibrated to the Lick/IDS system. Kinematic information is obtained for the sample. We analyse the line-strength index versus velocity dispersion relations for our sample of mainly low-density environment galaxies, and compare the slope of the relations with cluster galaxies from the literature. Our main findings are that the index-σ 0 relations presented for low-density regions are not significantly different from those of cluster E/S0s. The slope of the index-σ 0 relations does not seem to change for early-type galaxies of different environmental densities, but the scatter of the relations seems larger for group, field and isolated galaxies than for cluster galaxies.

High signal-to-noise, low-resolution spectra have been obtained for 22 globular clusters (GCs) in NGC 4365. Some of these were selected as probable representatives of an intermediate-age (2-5 Gyr), extremely metal-rich GC subpopulation. The presence of such a subpopulation had been inferred from the unusual optical and near-IR color distributions of GCs in this otherwise typical Virgo elliptical galaxy. However, ages derived from Lick indices are consistent with uniformly old mean ages for all GCs in our sample. The metallicities of the clusters show some evidence for a trimodal distribution. The most metal-poor and metal-rich peaks are consistent with the values expected for an elliptical galaxy of this luminosity, but there appears to be an additional, intermediate-metallicity peak lying between them. New Hubble Space Telescope photometry is consistent with this result. A plausible scenario is that in earlier data these three peaks merged into a single broad distribution. Our results suggest that it is difficult to identify intermediate-age GC subpopulations solely with photometry, even when both optical and near-infrared colors are used.Comment: 30 pages, including 11 figures. AJ in pres

Learning assessment at two-year colleges is growing, but not much has been published about it yet. In general, our smaller classrooms, diverse student population, high proportion of adjunct faculty, and academic freedom in teaching methods and tools set the stage for a different approach to assessment than at four-year institutions. This is the story of how faculty at Suffolk County Community College (SCCC) are working through a long-term assessment plan.