The physical properties and evolution of the interacting system AM 1204−292

Abstract

We investigate interaction effects in the stellar and gas kinematics, stellar population, and ionized gas properties of the interacting galaxy pair AM 1204−292,composed of NGC 4105 and NGC 4106. The data consist of long-slit spectra in the range 3000–7050 Å. The massive E3 galaxy NGC 4105 presents a flat stellar velocity profile, while the ionized gas is in strong rotation, suggesting an external origin. Its companion, NGC 4106, shows asymmetries in the radial velocity field, likely due to the interaction. The dynamics of the interacting pair were modelled using the P-Gadget3 treepm/sph code, from which we show that the system has just passed the first perigalacticum, which triggered an outbreak of star formation, currently at full maximum. We characterized the stellar population properties using the stellar population synthesis code starlight and, on average, both galaxies are predominantly composed of old stellar populations. NGC 4105 has a slightly negative age gradient, comparable with that of the most massive elliptical galaxies, but a steeper metallicity gradient. The SB0 galaxy NGC 4106 presents smaller radial variations in both age and metallicity in comparison with intermediate-mass early-type galaxies. These gradients have not been disturbed by interaction, since the star formation happened very recently and was not extensive in mass. Electron density estimates for the pair are systematically higher than those obtained in isolated galaxies. The central O/H abundances were obtained from photoionization models in combination with emission-line ratios, which resulted in 12 + log(O/H) = 9.03 ± 0.02 and 12 + log(O/H) = 8.69 ± 0.05 for NGC 4105 and NGC 4106, respectively.

Gas-phase metallicity determinations in nearby AGNs with SDSS-IV MaNGA: evidence of metal-poor accretion

“…Regarding the electron density effect on the strong-line calibrations, in general, NLRs of AGNs present higher N e values in comparison with the ones in the gas phase of H II re gions. F or instance, Copetti et al ( 2000 ), adopting the [S II ] λ6716/ λ6731 as an N e indicator, derived electron density values for a sample of galactic H II regions in the range of N e ≈ 20 − 400 cm −3 (see also, Krabbe et al 2014 ;Mora et al 2019 ;Buzzo et al 2021 ;Rosa et al 2021 ). On the other hand, electron density estimates in AGNs based on [S II ] λ6716/ λ6731 and [Ar IV ] λ4711/ λ4740 line ratios by Congiu et al ( 2017 ) show values ranging from ∼200 to 13 000 cm −3 (see also Freitas et al 2018 ;Kaddad et al 2018 ;Re v alski et al 2018 ;Mingozzi et al 2019 ;Davies et al 2020 ).…”