Search

We present a spatially resolved stellar population study of the inner ∼200 pc radius of NGC 4303 based on near-infrared integral field spectroscopy with SINFONI/VLT at a spatial resolution of 40–80 pc and using the starlight code. We found that the distribution of the stellar populations presents a spatial variation, suggesting an age stratification. Three main structures stand out. Two nuclear blobs, one composed by young stars (t ≤ 50 Myr) and one with intermediate-age stars (50 Myr < t ≤ 2 Gyr), both shifted from the centre. The third one is an internal intermediate-age spiral arm-like structure, surrounding the blob of young stars. Our results indicate that star formation has occurred through multiple bursts in this source. Furthermore, the youngest stellar populations (t ≲ 2 Gyr) are distributed along a circumnuclear star-forming ring with r ∼ 250 pc. The ring displays star formation rates (SFRs) in the range of 0.002–0.14 M⊙yr−1, favouring the 'pearls-on-a-string' scenario. The old underlying bulge stellar population component (t > 2 Gyr) is distributed outside the two blob structures. For the nuclear region (inner ∼60 pc radius) we derived an SFR of 0.43 M⊙ yr−1 and found no signatures of non-thermal featureless continuum and hot dust emission, supporting the scenario in which an LLAGN/LINER-like source is hidden in the centre of NGC 4303. Thus, our results reveal a rather complex star formation history in NGC 4303, with different stellar population components coexisting with a low efficiency accreting black hole in its centre. [ABSTRACT FROM AUTHOR]

We study how the spectral fitting of galaxies, in terms of light fractions, derived in one spectral region translates into another region, by using results from evolutionary synthesis models. In particular, we examine propagation dependencies on evolutionary population synthesis (EPS) models (, , Maraston and ), age, metallicity and stellar evolution tracks over the near-ultraviolet-near-infrared (NUV-NIR, 3500 Å to 2.5 μm) spectral region. Our main results are as follows: as expected, young ( Myr) stellar population fractions derived in the optical cannot be directly compared to those derived in the NIR, and vice versa. In contrast, intermediate to old age ( Myr) fractions are similar over the whole spectral region studied. The metallicity has a negligible effect on the propagation of the stellar population fractions derived from NUV to NIR. The same applies to the different EPS models, but restricted to the range between 3800 and 9000 Å. However, a discrepancy between /Maraston and / models occurs in the NIR. Furthermore, the initial mass function is not important for the synthesis propagation. Compared to synthesis results, our propagation predictions agree at ∼95 per cent confidence level in the optical, and ∼85 per cent in the NIR. In summary, spectral fitting performed in a restricted spectral range should not be directly propagated from the NIR to the UV/optical, or vice versa. We provide equations and an on-line form [panchromatic averaged stellar population (PaASP)] to be used for this purpose. [ABSTRACT FROM AUTHOR]

We present SOAR/OSIRIS cross-dispersed near-infrared (NIR) integrated spectra of 12 Galactic globular clusters that are employed to test Maraston NIR evolutionary population synthesis models, and to provide spectral observational constraints to calibrate future models. We measured equivalent widths () of the most prominent NIR absorption features: λ 1.49 μm, Mg λ 1.58 μm, Fe /Mg , λ 1.59 μm, Si , λ 1.71 μm, Mg , λ 2.21 μm, Na and λ 2.26 μm, Ca as well as the λ 1.62 μm, λ 2.29 μm, CO and λ 2.05 μm, CN molecular bands. Optical of G band (4300 Å), Hβ, Mg, Fe (4531, 527 and 5335 Å) and Na (5897 Å) were also measured. The globular clusters were compared with model predictions with ages within 4-15 Gyr, and metallicities between 0.005 and 2 . Observed integrated colours ( and ) were also compared with models. The NIR integrated spectra among our sample appear qualitatively similar in most of the absorption features. The Maraston models can properly predict the optical observed in globular clusters. Regarding the NIR, they do underestimate the strength of Mg 1.49 μm, but they can reproduce the observed of Fe 1.58 μm, Si 1.59 μm and CO 2.29 μm, in about half of our sample. The remaining objects require the inclusion of intermediate-age populations. Thus, we suggest that the presence of C- and O-rich stars in models is important to reproduce the observed strengths of metallic lines. Another possibility is the lack of α-enhancement in the models. In the case of the optical and NIR Fe lines, standard models and those that include blue horizontal branch stars produce similar results. A similar trend is observed for Na 5895 Å, while in the case of the G band, the models with blue horizontal branch do describe better the observations. For most of the sample, the optical to NIR colours are well described by the Maraston models. In general, Maraston models can provide reliable information on the NIR stellar population of galaxies, but only when and colours are taken together; in other words, and continuum fluxes should be simultaneously fitted. However, the results should be taken with caution, since the models tend to predict results biased towards young ages. [ABSTRACT FROM AUTHOR]

We present an observational study about the effects of the interactions in the kinematics, stellar population and abundances of the components of the galaxy pair AM 2306-721. Rotation curves for the main and companion galaxies were obtained, showing a deprojected velocity amplitude of 175 and 185 km s−1, respectively. The interaction between the main and companion galaxies was modelled using numerical N-body/hydrodynamical simulations, with the result indicating that the current stage of the merger would be about 250 Myr after perigalacticum. The spatial variation in the distribution of the stellar-population components in both galaxies was analysed by fitting combinations of stellar-population models of different age groups. The central region of main galaxy is dominated by an old (5–10 Gyr) population, while significant contributions from a young (200 Myr) and intermediate (1 Gyr) components are found in the disc, and being enhanced in the direction of the tidal features. The stellar population of the companion galaxy is overall much younger, being dominated by components with 1 Gyr or less, quite widely spread over the whole disc. Spatial profiles of the oxygen abundance were obtained from a grid of photoionization models using the R23 line ratio. The disc of the main galaxy shows a clear radial gradient, while the companion galaxy presents oxygen abundance relatively homogeneous across the disc. The absence of an abundance gradient in the secondary galaxy is interpreted in terms of mixing by gas flows from the outer parts to the centre of the galaxy due to the gravitational interaction with the more massive primary. [ABSTRACT FROM AUTHOR]