Kavli Affiliate: Luis C. Ho
| First 5 Authors: Jinning Liang, Fangzhou Jiang, Houjun Mo, Andrew Benson, Avishai Dekel
| Summary:
We study the connection between galaxy morphology and host dark matter (DM)
halo structure using cosmological simulations. Introducing a new kinematic
decomposition scheme, we robustly separate thin and thick discs and measure
halo properties, including cosmic web locations, internal structures, and
assembly histories. In the TNG50 simulation, we find that the
orbital-circularity threshold for disc differentiation varies systematically
with galaxy mass and redshift. Similarly, the energy threshold between stellar
halos and inner galaxies depends on mass and redshift, minimizing at
sub-Galactic halo mass where the circularity threshold approaches its peak.
Revisiting galaxy size predictors, we show that disc sizes in TNG50 correlate
with three structural parameters beyond virial mass and redshift: 1) a positive
correlation with halo spin $lambda$ across redshifts — stronger than
previously reported for zoom-in simulations but still weaker than the simple
$r_{1/2}/R_{rm vir} propto lambda$ scaling; 2) an anti-correlation with DM
concentration $c$; 3) larger discs in more actively accreting haloes. Disc mass
fraction is higher in rounder haloes and in cosmic knots and filaments,
implying that disc development needs both stable halo conditions and continuous
material supply. Our methodology is public and adaptable to other simulations.
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