Reorientation Rates of Structural and Kinematic Axes in Simulated Massive Galaxies and the Origins of Prolate Rotation

Abstract

In this work, we analyze a sample of $\sim$4000 massive ($M_{\ast }\ge 10^{11}{M}_{\odot }$ at $z=0$) galaxies in TNG300, the $(300\mathrm{Mpc}{)}^3$ box of the IllustrisTNG simulation suite. We characterize the shape and kinematics of these galaxies with a focus on the kinematic misalignment (${\Psi }_{\mathrm{int}}$) between the angular momentum (AM) and morphological major axis. We find that the traditional purely shape- or kinematics-based classifications are insufficient to characterize the diversity of our sample and define a new set of classes based on the rates of change of the galaxies' morphological and kinematic axes. We show that these classes are mostly stable over time and correspond to six distinct populations of galaxies: the rapid AM reorienters (58% of our sample), unsettled galaxies (10%), spinning disks (10%), twirling cigars (16%), misaligned slow reorienters (3%), and regular prolate rotators (galaxies that display major axis rotation; 2%). We demonstrate that the most-recent significant (mass-ratio $\mu >1/10$) mergers of these galaxies are the primary cause for their present-day properties and find that these mergers are best characterized at the point of the satellite's final infall -- that is, much closer to the final coalescence than has been previously thought. We show that regular prolate rotators evolve from spinning disk progenitors that experience a radial merger along their internal AM direction. Finally, we argue that these regular prolate rotators are distinct from the similarly-sized population of rapid AM reorienters with large ${\Psi }_{\mathrm{int}}$, implying that a large ${\Psi }_{\mathrm{int}}$ is not a sufficient condition for major axis rotation.

26 pages, 17 figures; accepted for publication in ApJ

References in corpus (14)

• The SAURON project -- IX. A kinematic classification for early-type galaxies
• Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge
• The Size Evolution of Star-forming and Quenched Galaxies in the IllustrisTNG simulation
• The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for disks in fast rotators
• P-MaNGA: Full spectral fitting and stellar population maps from prototype observations
• The diverse nature and formation paths of slow rotator galaxies in the EAGLE simulations
• CALIFA reveals Prolate Rotation in Massive Early-type Galaxies: A Polar Galaxy Merger Origin?
• Galaxies with prolate rotation in Illustris
• Formation of massive disk galaxies in the IllustrisTNG simulation
• The SLUGGS survey: combining stars, globular clusters and planetary nebulae to understand the assembly history of early-type galaxies from their large radii kinematics
• Accurate Identification of Galaxy Mergers with Stellar Kinematics
• Prospects for Recovering Galaxy Intrinsic Shapes from Projected Quantities
• Ubiquitous signs of interactions in early-type galaxies with prolate rotation
• Origin of stellar prolate rotation in a cosmologically simulated faint dwarf galaxy

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