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We study the formation of polar ring galaxies via minor mergers. We used N -body + hydrodynamics simulations to reproduce the dynamics of the observed system AM 2229-735 that is a minor merger whose interaction signals are those of a progenitor for a polar ring galaxy. We used the observational information of the system to get initial conditions for the orbit and numerical realizations of the galaxies to run the simulations. Our simulations reproduce the global characteristics of interaction observed in the system such as arms and a material bridge connecting the galaxies. As a merger remnant, we found a quasi-stable and self-gravitating planar tidal stream with dark matter, stars, and gas orbiting in a plane approximately perpendicular to the main galaxy disc leading in the future to a polar ring galaxy. We studied the dynamical conditions of the polar structure and found evidence suggesting that this kind of merger remnant can settle down in a disc-like structure with isothermal support, providing inspiring evidence about the process of formation of galactic discs and providing a potentially independent scenario to study the presence of dark matter in this kind of galaxies. [ABSTRACT FROM AUTHOR]

We present an observational study of the galaxy HRG 54103, a peculiar galaxy with an asymmetric disc ring. The main goal of this work is to study the stellar population and oxygen abundances for the inner bulge region. The kinematics derived from long-slit spectroscopy suggest that the line of nodes of the gaseous component of HRG 54103 is nearly along the galaxy ring minor axis. The gaseous disc seems to be kinematically decoupled relative to the morphology of the stellar ring. A small, but non-negligible, fraction of young stars (5-10 per cent) is estimated to contribute. This object is mainly dominated by old and intermediate stellar populations. The emission-line spectrum shows low-ionization nuclear emission-line region (LINER) type characteristics. We determined oxygen abundances using calibrations between this parameter and the strong emission line ratios known as the indices O3N2 and N2. Our results suggest a relatively homogeneous O/H across the minor axis of the galaxy, with average values of 12 + log(O/H)=8.4 dex and 12 + log(O/H)=8.7 dex, using the O3N2 and N2 parameters, respectively. These values are compatible with the few estimations of oxygen abundance for peculiar ring galaxies published in the literature. Implications on the formation history of HRG 54103 were investigated. [ABSTRACT FROM AUTHOR]

Gemini Multi-Object Spectrograph and its Integral Field Unit observational data were used to study the detailed 2D gas kinematics and morphological structures within the ~500 x 421 pc² of the active Seyfert 2 galaxy NGC 4501. We provide empirical pieces of evidence of possible outflowing material from the central zones of NGC 4501 to the observer. In addition, we performed a spectral synthesis and diagnostic diagram analysis to determine respectively the dominant stellar population in the inner disc of this galaxy and to unveil the actual nature of the central engine of NGC 4501. The principal finding of this work is that the central regions of NGC 4501 are dominated by non-circular motions connected to probable outflows of matter from the nuclear regions of this galaxy. A predominant old stellar population inhabits the internal zones of NGC 4501, excluding the possibility of ongoing starburst activity in the central parsecs of this galaxy. The latter result is confirmed by the diagnostic diagram analysis that establishes a preponderant active galactic nucleus character for NGC 4501. These outcomes together provide a general description of the gas motion and the corresponding nuclear activity in the internal disc of NGC 4501 in an attempt to elucidate the possible relation among the central activity and the induced kinematic properties of this nearby galaxy. [ABSTRACT FROM AUTHOR]

Aims. We report first results of an investigation of the tidally disturbed galaxy system AM546-324, whose two principal galaxies 2MFGC04711 and AM0546-324 (NED02) were previously classified as interacting doubles. This system was selected to study the interaction of ellipticals in a moderately dense environment. We provide spectral characteristics of the system and present an observational study of the interaction effects on the morphology, kinematics, and stellar population of these galaxies. Methods. The study is based on long-slit spectrophotometric data in the range of ∼4500-8000 Å obtained with the Gemini Multi- Object Spetrograph at Gemini South (GMOS-S). We have used the stellar population synthesis code STARLIGHT to investigate the star formation history of these galaxies. The Gemini/GMOS-S direct r-G0303 broad band pointing image was used to enhance and study fine morphological structures. The main absorption lines in the spectra were used to determine the radial velocity. Results. Along the whole long-slit signal, the spectra of the Shadowy galaxy (discovered by us), 2MFGC 04711, and AM0546-324 (NED02) resemble that of an early-type galaxy. We estimated redshifts of z = 0.0696, z = 0.0693 and z = 0.0718, corresponding to heliocentric velocities of 20 141 km s-1, 20 057 km s-1, and 20 754 km s-1 for the Shadowy galaxy, 2MFGC 04711 and AM0546-324 (NED02), respectively. The central regions of 2MFGC04711 and AM0546-324 (NED02) are completely dominated by an old stellar population of 2 × 109 < t ⩽ 13 × 109 yr and do not show any spatial variation in the contribution of the stellar-population components. Conclusions. The observed rotation profile distribution of 2MFGC 04711 and AM0546-324 (NED02) can be adequately interpreted as an ongoing stage of interaction with the Shadowy galaxy as the center of the local gravitational potential-well of the system. The three galaxies are all early-type. The extended and smooth distribution of the material in the Shadowy galaxy is a good laboratory to study direct observational signatures of tidal friction in action. [ABSTRACT FROM AUTHOR]

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 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 luminosity-weighted 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 cannot be discarded in the formation and evolution of early-type galaxies. [ABSTRACT FROM AUTHOR]