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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 present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300 Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for 15 galaxies in nine close pairs were used. The spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. Taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. This result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. We interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. We compared the estimated values of stellar and nebular extinction derived from the synthesis method and the Hα/Hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. We did not find any correlation between nebular and stellar metallicities. Neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich. [ABSTRACT FROM AUTHOR]

We employ the NASA Infrared Telescope Facility's near-infrared spectrograph SpeX at 0.8–2.4 μm to investigate the spatial distribution of the stellar populations (SPs) in the four well-known starburst galaxies: NGC 34, NGC 1614, NGC 3310 and NGC 7714. We use the starlight code updated with the synthetic simple SPs models computed by Maraston. Our main results are that the near-infrared light in the nuclear surroundings of the galaxies is dominated by young-/intermediate-age SPs (t ≤ 2 × 109 yr), summing from ∼40 up to 100 per cent of the light contribution. In the nuclear aperture of two sources (NGC 1614 and NGC 3310), we detected a predominant old SP component (t > 2 × 109 yr), while for NGC 34 and NGC 7714 the younger component prevails. Furthermore, we found evidence of a circumnuclear star formation ring-like structure and a secondary nucleus in NGC 1614, in agreement with previous studies. We also suggest that the merger/interaction experienced by three of the galaxies studied, NGC 1614, NGC 3310 and NGC 7714, can explain the lower metallicity values derived for the young SP component of these sources. In this scenario, the fresh unprocessed metal poorer gas from the destroyed/interacting companion galaxy is driven to the centre of the galaxies and mixed with the central region gas, before star formation takes place. In order to deepen our analysis, we performed the same procedure of SP synthesis using the Maraston & Strömbäck evolutionary population synthesis models. Our results show that the newer and higher resolution M11 models tend to enhance the old-/intermediate-age SP contribution over the younger ages. [ABSTRACT FROM PUBLISHER]

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]

We present a spectroscopic and photometric analysis for eight field galaxies in the direction of the galaxy cluster LCDCS-S001. The spectra were obtained with the GMOS instrument at the Gemini South Observatory. The objects were selected in an i′-band image and the multiobject spectroscopic observations were centred at 7500 Å. For the galaxies ID 440 and ID 461, we have determined redshifts of and 0.7465, respectively. For the other six galaxies we have confirmed the previous measurements of redshift. The redshifts of the field galaxies are in the range of . We determined the blue and visual luminosities and they are brighter than . The galaxies ID 180, ID 266 and ID 461 follow the Faber–Jackson relation of the Coma and Virgo early-type galaxies, and therefore do not present a brightening of the B luminosity as observed in galaxies at higher redshifts. The stellar velocity dispersion was measured for five galaxies (ID 146, ID 180, ID 266, ID 428 and ID 440) and estimated to be in the range of . Lick indices were measured and used to determine the stellar population properties of the galaxies ID 120 and ID 146, by means of spectral synthesis. The first galaxy, ID 120, presents in its spectrum absorption and emission lines, and we have found that the main contribution in the flux at λ5870 Å is of a 0.1-Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at λ4200 Å is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis, we estimated reddening values of and 0.82 for ID 120 and ID 146, respectively. According to classical diagnostic diagrams the emission lines present in the spectrum of ID 120 indicate that it is a starburst galaxy. [ABSTRACT FROM AUTHOR]

We present kinematic parameters and stellar population properties of selected galaxies in the high-redshift galaxy cluster LCDCS-S001, determined by spectroscopic data obtained with the Gemini multi-object spectrograph instrument in the Gemini South Observatory. The objects were selected in an i′-band cluster field image, and multi-object spectroscopic observations centred at 7500 Å were performed for 40 objects. Spectral features were successfully identified for 20 objects, and used to determine the redshift of the cluster. We found that 12 objects are cluster members and estimate a median redshift of 0.709 for this cluster. The relative velocities of the cluster members were used to estimate the projected cluster mass, which was found to be 3.54 × 10 14+2.33−1.41 M⊙. Lick and Dn(4000) indices were measured and used to determine the stellar population properties of the galaxies, by means of a spectral synthesis through Bruzual & Charlot evolutive models. We found that the bulk of stellar population for the cluster members has a spectrum compatible with solar metallicity and an age between 3.0 and 7.0 Gyr; with only one exception, the flux contribution of younger stars in the spectra does not exceed 25 per cent at 4200 Å. Emission [O ii] lines were detected for four galaxies, all of which showing a stronger contribution of young stars compared with other cluster galaxies. The equivalent width of the [O ii]λ3727 emission line was compared with Magris, Binette & Bruzual models for H ii regions. We found good correspondence between our values and the theoretical predictions for solar metallicity and with star formation time-scales . [ABSTRACT FROM AUTHOR]