We present an observational study about the impacts of the interactions in the electron density of H ii regions located in 7 systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300Å, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS). The electron density was determined using the ratio of emission lines [S II]λ6716/λ6731. 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 = 40−137cm −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 has emission lines excited by shocks, such as in AM 2322B (1 point), and AM 2322A (4 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 theses quantities especially when the metallicity is derived for these types of systems.
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 (N2 and O3N2). 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.
We present an observational study of the impacts of the interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for fifteen 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 the 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 behavior as being due to the effect of gas inflows along the disk of interacting galaxies on the star formation in a time scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of the pairs has a higher contribution of the young stellar population than the primary one. We compared the estimated values of the stellar and nebular extinctions derived from the synthesis method and the Hα/Hβ emission-line ratio finding that the 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. We neither found a correlation between stellar metalarXiv:1701.07054v1 [astro-ph.GA] 24 Jan 2017 2 Krabbe et al.licities and ages while a positive correlation between nebular metallicities and stellar ages was obtained, with the older regions being the most metal-rich.
In these proceedings we give a summary of the characteristics and current status of the MEGARA instrument, the future optical IFU and MOS for the 10.4-m Gran Telescopio Canarias (GTC). MEGARA is being built by a Consortium of public research institutions led by the Universidad Complutense de Madrid (UCM, Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The MEGARA IFU includes two different fiber bundles, one called LCB (Large Compact Bundle) with a field-of-view of 12.5×11.3 arcsec 2 and a spaxel size of 0.62 arcsec yielding spectral resolutions between R=6,800-17,000 and another one called SCB (Small Compact Bundle) covering 8.5×6.7 arcsec 2 with hexagonally-shaped and packed 0.42-arcsec spaxels and resolutions R=8,000-20,000. The MOS component allows observing up to 100 targets in 3.5×3.5 arcmin 2 . Both the IFU bundles and the set of 100 robotic positioners of the MOS will be placed at one of the GTC Folded-Cass foci while the spectrographs (one in the case of the MEGARA-Basic concept) will be placed at the Nasmyth platform. On March 2012 MEGARA passed the Preliminary Design Review and its first light is expected to take place at the end of 2015.
We present a detailed spatial analysis of stellar populations based on long-slit optical spectra in a sample of eight luminous early-type galaxies selected from nearby sparse groups and pairs, three of them may have interaction with another galaxy of similar mass. We have spatially measured luminosityweighted averages of age, [M/H], [Fe/H], and [α/Fe] in the sample galaxies to add empirical data relative to the influence of galaxy mass, environment, interaction, and AGN feedback in their formation and evolution. The stellar population of the individual galaxies were determined through the well-established stellar population synthesis code STARLIGHT using semi-empirical simple stellar population models. Radial variations of luminosity-weighted means of age, [M/H], [Fe/H], and [α/Fe] were quantified up to half of the effective radius of each galaxy. We found trends between representative values of age, [M/H], [α/Fe], and the nuclear stellar velocity dispersion. There are also relations between the metallicity/age gradients and the velocity dispersion. Contributions of 1 − 4 Gyr old stellar populations were quantified in IC 5328 and NGC 6758 as well as 4−8 Gyr old ones in NGC 5812. Extended gas is present in IC 5328, NGC 1052, NGC 1209, and NGC 6758, and the presence of a LINER is identified in all these galaxies. The regions up to one effective radius of all galaxies are basically dominated by α-enhanced metal-rich old stellar populations likely due to rapid star formation episodes that induced efficient chemical enrichment. On average, the age and [α/Fe] gradients are null and the [M/H] gradients are negative, although discordant cases were found. We found no correlation between the stellar population properties and the LINER presence as well as between the stellar properties and environment or gravitational interaction, suggesting that the influence of progenitor mass can-not be discarded in the formation and evolution of early-type galaxies.
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