Modern galaxy formation theory suggests that the misalignment between stellar and gaseous components usually results from an external gas accretion and/or interaction with other galaxies. The extreme case of the kinematic misalignment is demonstrated by so-called galaxies with counterrotation that possess two distinct components rotating in opposite directions with respect to each other. We provide an in-deep analysis of galaxies with counterrotation from IllustrisTNG100 cosmological simulations. We have found 25 galaxies with substantial stellar counterrotation in the stellar mass range of 2 × 109 − 3 × 1010 M⊙ . In our sample the stellar counterrotation is a result of an external gas infall happened ≈2 − 8 Gyr ago. The infall leads to the initial removal of pre-existing gas, which is captured and mixed together with the infalling component. The gas mixture ends up in the counterrotating gaseous disc. We show that $\approx 90\%$ of the stellar counterrotation formed in-situ, in the counterrotating gas. During the early phases of the infall, gas can be found in inclined extended and rather thin disc-like structures, and in some galaxies they are similar to (nearly-) polar disc or ring-like structures. We discuss a possible link between the gas infall, AGN activity and the formation of misaligned components. In particular, we suggest that the AGN activity does not cause the counterrotation, although it is efficiently triggered by the retrograde gas infall, and it correlates well with the misaligned component appearance. We also find evidence of the stellar disc heating visible as an increase of the vertical-to-radial velocity dispersion ratio above unity in both co- and counterrotating components, which implies the importance of the kinematical misalignment in shaping the velocity ellipsoids in disc galaxies.

This study presents a comprehensive chemodynamical analysis of LAMOST J1109+0754, a bright (V=12.8), extremely metal-poor ([Fe/H]=−3.17) star, with a strong r-process enhancement ([Eu/Fe]=+0.94 ± 0.12). Our results are based on the 7D measurements supplied by Gaia and the chemical composition derived from a high-resolution (R∼110,000), high signal-to-noise ratio ( ) S N 60 optical spectrum obtained by the 2.4 m Automated Planet Finder Telescope at Lick Observatory. We obtain chemical abundances of 31 elements (from lithium to thorium). The abundance ratios ([X/Fe]) of the light elements (Z30) suggest a massive Population III progenitor in the 13.4-29.5 M e mass range. The heavy-element (30<Z90) abundance pattern of J1109+075 agrees extremely well with the scaled-solar r-process signature. We have developed a novel approach to trace the kinematic history and orbital evolution of J1109+0754 with a cOsmologically deRIved timE-varyiNg Galactic poTential (the ORIENT) constructed from snapshots of a simulated Milky Way analog taken from the Illustris-TNG simulation. The orbital evolution within this Milky Way-like galaxy, along with the chemical abundance pattern, implies that J1109+0754 likely originated in a low-mass dwarf galaxy located ∼60 kpc from the center of the Galaxy, which was accreted ∼6-7 Gyr ago, and that the star now belongs to the outer-halo population. Unified AstronomyThesaurus concepts: Chemically peculiar stars (226); Population III stars (1285); R-process (1324); Stellar kinematics (1608); Chemical abundances (224); Stellar dynamics (1596); Orbits (1184); Galaxy dynamics (591)

Aims. We investigate the orbital and phase space properties of loss cone stars that interact strongly with a hard, high-redshift binary supermassive black hole (SMBH) system formed in a cosmological scenario. Methods. We use a novel hybrid integration approach that combines the direct N-body code φ-GRAPE with ETICS, a collisionless code that employs the self-consistent field method for force calculation. The hybrid approach shows considerable speed-up over direct summation for particle numbers > 106, while retaining accuracy of direct N-body for a subset of particles. During the SMBH binary evolution we monitor individual stellar interactions with the binary in order to identify stars that noticeably contribute to the SMBH binary hardening. Results. We successfully identify and analyze in detail the properties of stars that extract energy from the binary. We find that the summed energy changes seen in these stars match very well with the overall binary energy change, demonstrating that stellar interactions are the primary drivers of SMBH binary hardening in triaxial, gas-poor systems. We find that 76% of these stars originate from centrophilic orbits, only possible in a triaxial system. As a result, even the slight triaxiality of our system results in efficient refilling of the loss cone, avoiding the final parsec problem. We distinguish three different populations of interactions based on their apocenter. We find a clear prevalence of interactions co-rotating with the binary. Nevertheless, retrograde interactions are the most energetic, contributing only slightly less than the prograde population to the overall energy exchange. The most energetic interactions are also likely to result in a change of sign in the angular momentum of the star. We estimate the merger timescale of the binary to be ≈20 Myr, a value larger by a factor of two than the timescale reported in a previous study.