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Early-type Galaxy Spin Evolution in the Horizon-AGN Simulation
Choi, Hoseung,Yi, Sukyoung K.,Dubois, Yohan,Kimm, Taysun,Devriendt, Julien. E. G.,Pichon, Christophe American Astronomical Society 2018 The Astrophysical journal Vol.856 No.2
<P>Using the Horizon-AGN simulation data, we study the relative role of mergers and environmental effects in shaping the spin of early-type galaxies (ETGs) after z similar or equal to 1. We follow the spin evolution of 10,037 color-selected ETGs more massive than 10(10) M-circle dot that are divided into four groups: cluster centrals (3%), cluster satellites (33%), group centrals (5%), and field ETGs (59%). We find a strong mass dependence of the slow rotator fraction, f(SR), and the mean spin of massive ETGs. Although we do not find a clear environmental dependence of f(SR), a weak trend is seen in the mean value of the spin parameter driven by the satellite ETGs as they gradually lose their spin as their environment becomes denser. Galaxy mergers appear to be the main cause of total spin changes in 94% of the central ETGs of halos with M-vir > 10(12.5) M-circle dot, but only 22% of satellite and field ETGs. We find that non-mergerinduced tidal perturbations better correlate with the galaxy spin down in satellite ETGs than in mergers. Given that the majority of ETGs are not central in dense environments, we conclude that non-merger tidal perturbation effects played a key role in the spin evolution of ETGs observed in the local (z < 1) universe.</P>
On the Evolution of Galaxy Spin in a Cosmological Hydrodynamic Simulation of Galaxy Clusters
Choi, Hoseung,Yi, Sukyoung K. American Astronomical Society 2017 The Astrophysical journal Vol.837 No.1
<P>The traditional view of the morphology-spin connection is being challenged by recent integral field unit observations, as the majority of early-type galaxies are found to have a rotational component that is often as large as a dispersion component. Mergers are often suspected to be critical in galaxy spin evolution, yet the details of their roles are still unclear. We present the first results on the spin evolution of galaxies in cluster environments through a cosmological hydrodynamic simulation. Galaxies spin down globally with cosmic evolution. Major (mass ratios > 1/4) and minor ( 1/4 >= mass ratios > 1/50) mergers are important contributors to the spin-down in particular in massive galaxies. Minor mergers appear to have stronger cumulative effects than major mergers. Surprisingly, the dominant driver of galaxy spin-down seems to be environmental effects rather than mergers. However, since multiple processes act in combination, it is difficult to separate their individual roles. We briefly discuss the caveats and future studies that are called for.</P>