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Dametto N.Z.,Federal University of Rio Grande do Sul | Riffel R.,Federal University of Rio Grande do Sul | Pastoriza M.G.,Federal University of Rio Grande do Sul | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica Mcti | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

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. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Riffel R.,Federal University of Rio Grande do Sul | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica Mcti | Aleman I.,Federal University of Rio Grande do Sul | Brotherton M.S.,University of Wyoming | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the kinematics and excitation mechanisms of H2 and [Fe II] lines in a sample of 67 emission-line galaxies with Infrared Telescope Facility SpeX near-infrared (0.8-2.4 μm) spectroscopy together with new photoionization models. H2 emission lines are systematically narrower than narrow-line region lines, suggesting that the two are, very likely, kinematically disconnected. The new models and emission-line ratios show that the thermal excitation plays an important role not only in active galactic nuclei but also in star-forming galaxies. The importance of the thermal excitation in star-forming galaxies may be associated with the presence of supernova remnants close to the region emitting H2 lines. This hypothesis is further supported by the similarity between vibrational and rotational temperatures of H2. We confirm that the diagram involving the line ratios H2 2.121 μm/Brγ and [Fe II] 1.257 μm/Paβ is an efficient tool for separating emission-line objects according to their dominant types of activities. We suggest new limits to the line ratios in order to discriminate between the different types of nuclear activities. © Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Fraga L.,Southern Observatory for Astrophysical Research | Fraga L.,Laboratorio Nacional Of Astrofisica Mcti | Kunder A.,Cerro Tololo Inter American Observatory | Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2013

We present high-quality BVRI photometric data in the field of globular cluster NGC 6496 obtained with the SOAR Telescope Adaptive Module (SAM). Our observations were collected as part of the ongoing SAM commissioning. The distance modulus and cluster color excess as found from the red clump are (m-M)V = 15.71 ± 0.02 mag and E(V-I) = 0.28 ± 0.02 mag. An age of 10.5 ± 0.5 Gyr is determined from the difference in magnitude between the red clump and the subgiant branch. These parameters are in excellent agreement with the values derived from isochrone fitting. From the color-magnitude diagram we find a metallicity of [Fe/H] = -0.65 dex and hence support a disk classification for NGC 6496. The complete BVRI data set for NGC 6469 is made available in the electronic edition of the Journal. © 2013. The American Astronomical Society. All rights reserved. Source

Amores E.B.,University of Lisbon | Amores E.B.,Laboratorio Nacional Of Astrofisica Mcti | Sodre L.,University of Sao Paulo | Minniti D.,University of Santiago de Chile | And 9 more authors.
Astronomical Journal | Year: 2012

VISTA Variables in the Via Láctea (VVV) is an ESO variability survey that is performing observations in near-infrared bands (ZY JHK s) toward the Galactic bulge and part of the disk with the completeness limits at least 3mag deeper than Two Micron All Sky Survey. In the present work, we searched in the VVV survey data for background galaxies near the Galactic plane using ZY JHK s photometry that covers 1.636deg2. We identified 204 new galaxy candidates by analyzing colors, sizes, and visual inspection of multi-band (ZY JHK s) images. The galaxy candidate colors were also compared with the predicted ones by star count models considering a more realistic extinction model at the same completeness limits observed by VVV. A comparison of the galaxy candidates with the expected one by Millennium simulations is also presented. Our results increase the number density of known galaxies behind the Milky Way by more than one order of magnitude. A catalog with galaxy properties including ellipticity, Petrosian radii, and ZY JHK s magnitudes is provided, as well as comparisons of the results with other surveys of galaxies toward the Galactic plane. © © 2012. The American Astronomical Society. All rights reserved.. Source

Paunzen E.,Masaryk University | Iliev I.K.,Bulgarian Academy of Science | Pintado O.I.,Instituto Superior Of Correlacion Geologica | Baum H.,University of Vienna | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Δ photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrowband system measures the flux distribution in the region from 4900 to 5600 Å in order to find any peculiarities around 5200 Å. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Δa photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3s detection limit of each globular cluster, about 3 per cent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies. © 2014 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

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