The diverse nature and formation paths of slow rotator galaxies in the eagle simulations

Abstract

We use a sample of z = 0 galaxies visually classified as slow rotators (SRs) in the eagle hydrodynamical simulations to explore the effect of galaxy mergers on their formation, characterise their intrinsic galaxy properties, and study the connection between quenching and kinematic transformation. SRs that have had major or minor mergers (mass ratios ≥0.3 and 0.1 − 0.3, respectively) tend to have a higher triaxiality parameter and ex-situ stellar fractions than those that had exclusively very minor mergers or formed in the absence of mergers (“no-merger” SRs). No-merger SRs are more compact, have lower black hole-to-stellar mass ratios and quenched later than other SRs, leaving imprints on their z = 0 chemical composition. For the vast majority of SRs we find that quenching, driven by active galactic nuclei feedback, precedes kinematic transformation, except for satellite SRs, in which these processes happen in tandem. However, in ≈50 per cent of these satellites, satellite-satellite mergers are responsible for their SR fate, while environment (i.e. tidal field and interactions with the central) can account for the transformation in the rest. By splitting SRs into kinematic sub-classes, we find that flat SRs prefer major mergers; round SRs prefer minor or very minor mergers; prolate SRs prefer gas-poor mergers. Flat and prolate SRs are more common among satellites hosted by massive haloes ($>10^{13.6}\, \rm M_{\odot }$) and centrals of high masses ($M_{\star } > 10^{10.5}\, \rm M_{\odot }$). Although eagle galaxies display kinematic properties that broadly agree with observations, there are areas of disagreement, such as inverted stellar age and velocity dispersion profiles. We discuss these and how upcoming simulations can solve them.

The physical connection between central stellar surface density and stellar spin in SAMI and MaNGA nearby galaxies

“…Excitingly, the potential disconnect between quenching and morphological transformation as well as the large variety of mergerdriven kinematic changes in galaxies suggested here appear in line with predictions from large hydro-dynamical cosmological simulations such as EAGLE (e.g., Lagos et al 2018Lagos et al , 2022 IllustrisTNG (e.g., Tacchella et al 2019;Park et al 2021). However, it is important to note that some of these findings may be affected by spurious collisional heating (Ludlow et al 2021) and next generation/higher resolution runs are needed to fully confirm these scenarios and allow us to perform a quantitative comparison between observations and simulations (see also van de Sande et al 2019).…”

The evolution of the oxygen abundance gradients in star-forming galaxies in the eagle simulations

“…Positive metallicity gradients could also be related to positive age profiles since the new stars formed in the inner region would contribute to flattening or inverting the age slopes, depending on the relative contributions of coe v al stellar populations. Previous works on dispersion-dominated systems in the EAGLE simulations showed a fraction of rejuvenated systems with positive age gradients (Rosito et al 2019a , b ), which seems to be in excess compared to observations (Lagos et al 2022 ). On the other hand, Varela-Lavin et al ( 2021) analysed the age profiles and mass surface density of disc-dominated system in an EAGLE simulation and reported the existence of a significant fraction of disc-dominated galaxies with ongoing central star formation activity and positive age profiles.…”

The SAMI Galaxy Survey: The Link Between [$α$/Fe] and Kinematic Morphology

“…More recently, these results have been reinforced by Lagos et al (2021), who investigated slow rotator formation scenarios in the EA-GLE simulation. They explicitly computed the expected chemical abundances for each assembly history, as a function of galaxy radius.…”

“…Considering later morphological types, we note that substantial number of spiral and lenticular galaxies can be separated out into two distinct components, a central bulge, and an extended disk. Under the inside-out scenario of galaxy formation, so-called classical bulges are thought to form through violent gas collapse or mergers (Larson 1974;Bender et al 1992) over short timescales, with the disk gradually building up around them. In this scenario, disk-dominated galaxies will have had a longer overall duration of star formation relative to bulge-dominated galaxies, and show a greater degree of rotational support.…”