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[en] We present a new approach for population synthesis in galaxy nuclei, which makes use, exclusively, of a library of integrated spectra of star clusters. This method has given interesting results for nearby galaxy nuclei in terms of dating successive stellar generations and detecting bursts of star formation, as well as of determining the chemical enrichment. These population syntheses results for galaxy nuclei are then compared to those derived from an evolutionary method. The two different approaches are interfaced by means of theoretical M/LV ratios for single generation stellar systems computed for differing ages. We conclude that results from the population synthesis are compatible with chemical evolution models. This confrontation allows the star formation history in galaxy nuclei to be derived. (author)
[en] We have isolated the emission-line component in a sample of 92 galaxies using stellar absorption templates built from emission-free star cluster spectra. All sources of reddening extrinsic to the line emitting regions have been properly taken into account. A statistical analysis of the emission line properties has been carried out. We conclude, in particular, that the [NII]λλ6548, 84 lines are slightly more sensitive to metallicity effects than the [SII]λλ6717, 31 lines. However, both [NII] and [SII] lines are as well dependent on the excitation mechanism. From a subsample of 76 galaxies we have built three characteristic average spectra corresponding to (i) nuclear HII regions, (ii) objects identified as LINERS and (iii) extreme low-level emission galaxies with Wem(Hα)≤2A. We conclude from the [SII]λλ6717, 6731/[SIII]λλ9069, 9532 line ratio that shock ionization is the mechanism at work in extreme low-level emission galaxies
[en] The integrated spectrum of the rich open cluster M 11 was synthesized with a library of stellar spectra. The availability of a significant number of stars in a color-magnitude diagram (CMD) allows for the study of the missing fainter stellar component by means of an integrated light synthesis technique. The CMD-aided synthesis tests, carried out with the integrated spectrum of M 11, confirm the necessity for astrophysically plausible constraints to be used in conjunction with fitting algorithms in population syntheses. These tests are particularly relevant for the population syntheses of more complex objects like galaxy nuclei, when stellar libraries are used. 26 refs
[en] We analyse the stellar population and the emitting gas in the inner 2-5 kpc of a sample of nine Seyfert 2 galaxies, using 5-A resolution spectra in the range 3600-7000 A. The typical population is old and moderately stronglined, except in IC 5135 which presents star-forming events. The emission-line spectrum is studied after subtraction of the stellar population. Broad Hα components were found for five of the galaxies. The line widths correlate with the critical densities for the forbidden lines in four of the galaxies and with the ionization potential in three of these, indicating the presence of density stratification and ionization structure. Comparison of our emission-line ratios with smaller aperture data obtained from the literature reveal important changes in the values due to contamination by surrounding gas. (author)
[en] In this study, we have applied to the blueish nuclei of the spiral galaxies M33 and NGC 278 and to the dwarf lenticular NGC 404, a population synthesis method relying upon a base of star clusters, over the range 3700-9700 A. We make use of a grid of star cluster spectral features as a function of age and metallicity. Whenever necessary, we refine this first approach by using the entire spectrum points directly. The algorithms employed are, in the first case a multiple minimization procedure with a statistical treatment of the acceptable solutions, and, in the second case a classical minimization procedure. (author)
[en] We simulate in this paper the occurrence of star formation events superimposed on old populations, during the last 3 x 109 yr, by combining star cluster integrated spectra of different ages with those of red strong-lined galaxy nuclei. As the young star clusters have metallicities in the range - 0.5 < [Z/Z(solar)]≤0, our simulation address in particular the case of starbursts induced by galaxy interactions bringing fresh, low-metallicity gas to the host galaxy. We follow the evolution of the composite spectrum for burst to old population mass ratios of 10, 1 and 0.1 per cent. We present also the effects of the starburst on the restframe BVRI magnitudes and colours, as well as on the equivalent widths (Wlambda) for a set of metallic and Balmer lines. (author)
[en] We provide evidence that indicates the star cluster Pfleiderer 2, which is projected in a rich field, as a newly identified Galactic globular cluster. Since it is located in a crowded field, core extraction and decontamination tools were applied to reveal the cluster sequences in B, V, and I color-magnitude diagrams (CMDs). The main CMD features of Pfleiderer 2 are a tilted red giant branch and a red horizontal branch, indicating a high metallicity around solar. The reddening is E(B - V) = 1.01. The globular cluster is located at a distance of d sun = 16 ± 2 kpc from the Sun. The cluster is located 2.7 kpc above the Galactic plane and at a distance of R GC = 9.7 kpc from the Galactic center, which is unusual for a metal-rich globular cluster.
[en] The metallicity distribution and abundance ratios of the Galactic bulge are reviewed. Issues raised by recent work of different groups, in particular the high metallicity end, the overabundance of α-elements in the bulge relative to the thick disc and the measurement of giants versus dwarfs, are discussed. Abundances in the old moderately metal-poor bulge globular clusters are described.