ALBERT

Description: We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method, via the direct T e -method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the T e -method underestimates the oxygen abundances by up to ~2 dex (with averaged value of ~0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called ‘temperature problem’ in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (~2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.

Description: We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method, via the direct T e -method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the T e -method underestimates the oxygen abundances by up to ~2 dex (with averaged value of ~0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called ‘temperature problem’ in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (~2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.

Description: We have used observational spectroscopic data of star-forming regions compiled from the literature and photoionization models to analyse the neon ionic abundances obtained using both optical and mid-infrared emission lines. Comparing Ne ++ /H + ionic abundances from distinct methods, we have found that, on average, the abundances obtained via infrared emission lines are higher than those obtained via optical lines, by a factor of 4. Photoionization models with abundance variations along the radius of the hypothetical nebula provide a possible explanation for a large part of the difference between ionic abundances via optical and infrared emission lines. The ionization correction factor (ICF) for the neon is obtained from direct determinations of ionic fractions using infrared emission lines. We derive a constant Ne/O ratio (log Ne/O  –0.70) for a large range of metallicities, independently of the ICF used to compute the neon total abundance.

Description: We investigate interaction effects on the dynamics and morphology of the galaxy pairs AM 2058-381 and AM 1228-260. This work is based on r ' images and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the Gemini South Telescope. The luminosity ratio between the main (AM 2058A) and secondary (AM 2058B) components of the first pair is a factor of ~ 5, while for the other pair, the main (AM 1228A) component is 20 times more luminous than the secondary (AM 1228B). The four galaxies have pseudo-bulges, with a Sérsic index n  〈 2. Their observed radial velocities profiles (RVPs) present several irregularities. The receding side of the RVP of AM 2058A is displaced with respect to the velocity field model, while there is a strong evidence that AM 2058B is a tumbling body, rotating along its major axis. The RVPs for AM 1228A indicate a misalignment between the kinematic and photometric major axes. The RVP for AM 1228B is quite perturbed, very likely due to the interaction with AM 1228A. NFW halo parameters for AM 2058A are similar to those of the Milky Way and M 31. The halo mass of AM 1228A is roughly 10 per cent that of AM 2058A. The mass-to-light (M/L) of AM 2058 agrees with the mean value derived for late-type spirals, while the low M/L for AM 1228A may be due to the intense star formation ongoing in this galaxy.

Description: We present an observational study of the interaction effect on the dynamics and morphology of the minor merger AM 1219–430. This work is based on r ' and g ' images and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the Gemini South Telescope. We detected a tidal tail in the main galaxy (AM 1219A) and a bridge of material connecting the galaxies. In luminosity, AM 1219A is about 3.8 times brighter than the secondary (AM 1219B). The surface brightness profile of AM 1219A was decomposed into bulge and disc components. The profile shows a light excess of ~53 per cent due to the contribution of star-forming regions, which is typical of starburst galaxies. On the other hand, the surface brightness profile of AM 1219B shows a lens structure in addition to the bulge and disc. The scalelengths and central magnitudes of the disc structure of both galaxies agree with the average values derived for galaxies with no sign of ongoing interaction or disturbed morphology. The Sérsic index ( n  〈 2), the effective and scale radii of the bulge of both galaxies are typical of pseudo-bulges. The rotation curve of AM 1219A derived from the emission line of ionized gas is quite asymmetric, suggesting a gas perturbed by interaction. We explore all possible values of stellar and dark matter masses. The overall best-fitting solution for the mass distribution of AM 1219A was found with M/L for bulge and disc of $\Upsilon _{\rm b}=2.8_{-0.4}^{+0.4}$ and $\Upsilon _{\rm d}=2.4_{-0.2}^{+0.3}$ , respectively, and a Navarro et al. profile of $M_{200}=2.0_{-0.4}^{+0.5}\times 10^{12}\,\mathrm{M}_{{\odot }}$ and $c=16.0_{-1.1}^{+1.2}$ . The estimated dynamical mass is 1.6 10 11 M , within a radius of ~10.6 kpc.

Description: In this paper, we derive oxygen abundance gradients from H ii regions located in 11 galaxies in eight systems of close pairs. Long-slit spectra in the range 4400–7300 Å were obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). Spatial profiles of oxygen abundance in the gaseous phase along galaxy discs were obtained using calibrations based on strong emission lines ( N 2 and O 3 N 2). We found oxygen gradients to be significantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM 1219A, AM 1256B, AM 2030A and AM 2030B, show a clear break in the oxygen abundance at galactocentric radius R / R 25 between 0.2 and 0.5. For AM 1219A and AM 1256B, we found negative slopes for the inner gradients, and for AM 2030B, we found a positive slope. All three cases show a flatter behaviour to the outskirts of the galaxies. For AM 2030A, we found a positive slope for the outer gradient, while the inner gradient is almost compatible with a flat behaviour. We found a decrease of star formation efficiency in the zone that corresponds to the oxygen abundance gradient break for AM 1219A and AM 2030B. For the former, a minimum in the estimated metallicities was found very close to the break zone, which could be associated with a corotation radius. However, AM 1256B and AM 2030A, present a star formation rate maximum but not an extreme oxygen abundance value. All four interacting systems that show oxygen gradient breaks have extreme SFR values located very close to break zones.The H ii regions located in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies.

Description: We analysed the evolution of the metallicity of the gas with the redshift for a sample of AGNs in a very wide redshift range (0 〈 z  〈 4) using ultraviolet emission lines from the narrow-line regions (NLRs) and photoionization models. The new index C43 = log[(C iv +C iii ])/He ii ] is suggested as a metallicity indicator for AGNs. Based on this indicator, we confirmed the no metallicity evolution of NLRs with the redshift pointed out by previous works. We found that metallicity of AGNs shows similar evolution than the one predicted by cosmic semi-analytic models of galaxy formation set within the cold dark matter merging hierarchy (for z 3). Our results predict a mean metallicity for local objects in agreement with the solar value (12+log( O /H)=8.69). This value is about the same that the maximum oxygen abundance value derived for the central parts of local spiral galaxies. Very low metallicity log ( Z /Z )  –0.8 for some objects in the range 1.5 〈 z 〈 3 is derived.

Description: We present an observational study about the impacts of the interactions on the electron density of H ii regions located in seven systems of interacting galaxies. The data consist of long-slit spectra in the range 4400–7300 Å, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). The electron density was determined using the ratio of emission lines [S ii ] 6716/6731. Our results indicate that the electron density estimates obtained of H ii regions from our sample of interacting galaxies are systematically higher than those derived for isolated galaxies. The mean electron density values of interacting galaxies are in the range of N e  = 24–532 cm –3 , while those obtained for isolated galaxies are in the range of N e  = 40–137 cm –3 . Comparing the observed emission lines with predictions of photoionization models, we verified that almost all the H ii regions of the galaxies AM 1054A, AM 2058B and AM 2306B have emission lines excited by shock gas. For the remaining galaxies, only few H ii regions have emission lines excited by shocks, such as in AM 2322B (one point) and AM 2322A (four points). No correlation is obtained between the presence of shocks and electron densities. Indeed, the highest electron density values found in our sample do not belong to the objects with gas shock excitation. We emphasize the importance of considering these quantities especially when the metallicity is derived for these types of systems.