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Analyses of the polycyclic aromatic hydrocarbon (PAH) feature profiles, especially the 6.2 $��$m feature, could indicate the presence of nitrogen incorporated in their aromatic rings. In this work, 155 predominantly starburst-dominated galaxies (including HII regions and Seyferts, for example), extracted from the Spitzer/IRS ATLAS project (Hern��n-Caballero & Hatziminaoglou 2011), have their 6.2 $��$m profiles fitted allowing their separation into the Peeters' A, B and C classes (Peeters et al. 2002). 67% of these galaxies were classified as class A, 31% were as class B and 2% as class C. Currently class A sources, corresponding to a central wavelength near 6.22 $��$m, seem only to be explained by polycyclic aromatic nitrogen heterocycles (PANH, Hudgins et al. 2005), whereas class B may represent a mix between PAHs and PANHs emissions or different PANH structures or ionization states. Therefore, these spectra suggest a significant presence of PANHs in the interstellar medium (ISM) of these galaxies that could be related to their starburst-dominated emission. These results also suggest that PANHs constitute another reservoir of nitrogen in the Universe, in addition to the nitrogen in the gas phase and ices of the ISM.

Mid-infrared (MIR) spectra observed with Gemini/Michelle were used to study the nuclear region of the Compton-thick Seyfert 2 (Sy 2) galaxy Mrk 3 at a spatial resolution of $\sim$200 pc. No polycyclic aromatic hydrocarbons (PAHs) emission bands were detected in the N-band spectrum of Mrk 3. However, intense [Ar III] 8.99 $\mu$m, [S IV] 10.5 $\mu$m and [Ne II] 12.8 $\mu$m ionic emission-lines, as well as silicate absorption feature at 9.7$\mu$m have been found in the nuclear extraction ($\sim$200 pc). We also present subarcsecond-resolution Michelle N-band image of Mrk 3 which resolves its circumnuclear region. This diffuse MIR emission shows up as a wings towards East-West direction closely aligned with the S-shaped of the Narrow Line Region (NLR) observed at optical [O III]$\lambda$5007\AA image with Hubble/FOC. The nuclear continuum spectrum can be well represented by a theoretical torus spectral energy distribution (SED), suggesting that the nucleus of Mrk 3 may host a dusty toroidal structure predicted by the unified model of active galactic nucleus (AGN). In addition, the hydrogen column density (N$_H\,=\,4.8^{+3.3}_{-3.1}\times\,10^{23}$ cm$^{-2}$) estimated with a torus model for Mrk 3 is consistent with the value derived from X-ray spectroscopy. The torus model geometry of Mrk 3 is similar to that of NGC 3281, both Compton-thick galaxies, confirmed through fitting the 9.7$\mu$m silicate band profile. This results might provide further evidence that the silicate-rich dust can be associated with the AGN torus and may also be responsible for the absorption observed at X-ray wavelengths in those galaxies., Comment: 11 pages, 6 figures

We present mid infrared (Mid-IR) spectra of the Compton-thick Seyfert 2 galaxy NGC\,3281, obtained with the Thermal-Region Camera Spectrograph (T-ReCS) at the Gemini South telescope. The spectra present a very deep silicate absorption at 9.7\,$��$m, and [S{\sc\,iv]}\,10.5\,$��$m and [Ne{\sc\,ii]}\,12.7\,$��$m ionic lines, but no evidence of PAH emission. We find that the nuclear optical extinction is in the range 24 $\leq$ A$_{V}$ $\leq$ 83\,mag. A temperature T = 300\,K was found for the black-body dust continuum component of the unresolved 65\,pc nucleus and at 130\,pc SE, while the region at 130\,pc reveals a colder temperature (200\,K). We describe the nuclear spectrum of NGC\,3281 using a clumpy torus model that suggests that the nucleus of this galaxy hosts a dusty toroidal structure. According to this model, the ratio between the inner and outer radius of the torus in NGC\,3281 is $R_0/R_d$ = 20, with {\bf 14} clouds in the equatorial radius with optical depth of $��_{V}$ = 40\,mag. We would be looking in the direction of the torus equatorial radius ($i$ = {\bf 60$^{\circ}$}), which has outer radius of R$_{0}\,\sim$ 11\,pc. The column density is N$_{H}\approx$\,{\bf 1.2}\,$\times\,10^{24}\,cm^{-2}$ and iron K$��$ equivalent width ($\approx$ 0.5 - 1.2\,keV) are used to check the torus geometry. Our findings indicate that the X-ray absorbing column density, which classifies NGC\,3281 as a Compton-thick source, may also be responsible for the absorption at 9.7\,$��$m providing strong evidence that the silicate dust responsible for this absorption can be located in the AGN torus., Accepted by ApJ

We present an observational study about the impacts of the interactions in the kinematics, stellar populations, and oxygen abundances of the components of the galaxy pair AM\,2322-821. A fairly symmetric rotation curve for the companion (AM\,2322B) galaxy with a deprojected velocity amplitude of 110 km s$^{-1}$ was obtained, and a dynamical mass of $ 1.1 - 1.3 \times 10^{10} M_{\sun}$ within a radius of 4 kpc was estimated using this deprojected velocity. Asymmetries in the radial velocity field were detected for the companion, very likely due the interaction between the galaxies. 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 system would be about 90 Myr after perigalacticum. The spatial variation in the distribution of the stellar-population components in both galaxies was analysed using the stellar population synthesis code {\sc STARLIGHT}. The companion galaxy is dominated by a very young (t $ \leq 1\times10^{8}$ yr) population, with the fraction of this population to the total flux at $\lambda\, 5\,870\, \AA$, increasing outwards in the galaxy disc. On the other hand, the stellar population of AM\,2322A is heterogeneous along the slit positions observed. Spatial profiles of oxygen abundance in the gaseous phase were obtained using the diagnostic diagram R23 vs. [OIII]/[OII], where we compared the observed values with the ones obtained from photoionization models. Such gradients of oxygen abundance are significantly flatter for this pair of galaxies than in typical isolated spiral galaxies. This metallicity distribution is interpreted as the gradients having been destroyed by interaction-induced gas flows from the outer parts to the centre of the galaxy, Comment: accepted by MNRAS

We present SOAR/OSIRIS cross-dispersed NIR integrated spectra of 12 Galactic globular clusters that are employed to test Maraston (2005, M05) NIR EPS models, and to provide spectral observational constraints to calibrate future models. We measured Ew of the most prominent NIR absorption features. Optical Ew were also measured. The globular clusters Ew were compared with model predictions with ages within 4-15 Gyr, and metallicities between 1/200 and 2 Zsun. Observed integrated colours were also compared with models. The NIR integrated spectra among our sample appear qualitatively similar in most the absorption features. The M05 models can properly predict the optical Ew observed in globular clusters. Regarding the NIR, they do underestimate the strength of Mg I 1.49mum, but they can reproduce the observed Ew of Fe I 1.58mum, Si I 1.59mum, and CO 2.29mum, 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 alpha-enhancement in the models. In the case of the optical and NIR Fe I lines, standard models and those that include blue horizontal branch stars, produce similar results. A similar trend is observed for Na I 5895A, 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 M05 models. In general, M05 models can provide reliable information on the NIR stellar population of galaxies, but only when Ew and colours are taken together, in other words, Ew 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., Comment: 11 pages, 10 Figures, Accepted by MNRAS

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 AM2306-721. Rotation curves for the main and companion galaxies were obtained, showing a deprojected velocity amplitude of 175 km/s and 185 km/s, respectively. The interaction between the main and companion galaxies was modeled 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 disk, 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 disk. Spatial profiles of the oxygen abundance were obtained from the a grid of photoionization models using the R23 line ratio. The disk of the main galaxy shows a clear radial gradient, while the companion galaxy presents an oxygen abundance relatively homogeneous across the disk. 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 center of the galaxy due to the gravitational interaction with the more massive primary., Comment: 13 pages, 12 figures, accepted for publication on MNRAS

Context: The spatial distribution of the stellar populations inside a spheroidal system and their kinematical properties supply important informations about the formation process. Aims: We have performed a detailed stellar population analysis using long slit spectroscopic observations up to almost one effective radius of two different early-type galaxies of low density regions of the local Universe: NGC 1052, a E4 Liner prototype of a loose group that has a stellar rotating disc, and NGC 7796, a E1 of the field which shows a kinematically distinct core. The mean luminosity-weighted stellar age, metallicity, and alpha/Fe ratio along both photometric axes of them have been obtained in order to reconstruct the star formation history in their kinematically distinct subsystems. Methods: We have measured Lick indices and computed their radial gradients. They were compared with the predicted ones of simple stellar population models. We have also applied a stellar population synthesis. Results: The star characteristics are associated with their kinematics: they are older and alpha-enhanced in the bulge of NGC 1052 and core of NGC 7796, while they show a strong spread of alpha/Fe and age along the disc of NGC 1052 and an outwards radial decreasing of them outside the core of NGC 7796. The age variation is possibly connected to the alpha/Fe one. Conclusions: Both galaxies were formed by processes in which the star formation occurred firstly at the bulge (NGC 1052) and nucleus (NGC 7796) 12-15 Gyr ago on short timescales (0.1-1 Gyr) providing an efficient chemical enrichment by SN-II. In the disc of NGC 1052, there is some spread of age and formation timescales around its stars. In NGC 7796, the star formation timescale had some outwards radial increasing along both axes., Comment: 26 pages, 27 figures, accepted for publication in A&A

We present 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 in the Gemini South Observatory. The objects were selected in an i' band image and the multi-object spectroscopic observations were centered at 7500 A. For the galaxies ID 440 and ID 461 we have determined redshifts of z=0.7464 and z=0.7465, respectively. For the other six galaxies we have confirmed the redshift calculated by Rembold & Pastoriza (2006). The redshifts of the field galaxies are in the range of 0.2201 < z < 0.7784. We determined the blue and visual luminosities and they are brighter than M_B=-18.64. The galaxies ID 180, ID 266, 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 and estimated to be in the range of 200 < sigma < 346 km/s. Lick indices were measured and used to determine the stellar population properties of 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 lambda 5870 A is of a 0.1 Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at lambda 4200 A, is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis we estimated reddening values of E(B-V)=0.90 and E(B-V)=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., Accepted for publication in Monthly Notices of the Royal Astronomical. 6 Figures and 4 tables

We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line ftuxes. The light curves for the con­ tinuum ftuxes exhibited two well-defined local mínima or "dips," the first lasting