Kavli Affiliate: Luis C. Ho
| First 5 Authors: Jinning Liang, Fangzhou Jiang, Houjun Mo, Andrew Benson, Avishai Dekel
| Summary:
We present a series of studies on the connection between galaxy morphology
and the structure of host dark-matter (DM) haloes using cosmological
simulations. In this work, we introduce a new kinematic decomposition scheme
that features physical identification of morphological components, enabling
robust separation of thin and thick discs; and measure a wide range of halo
properties, including their locations in the cosmic web, internal structures,
and assembly histories. Our analysis of the TNG50 simulation reveals that the
orbital-circularity threshold for disc differentiation varies across galaxies,
with systematic trends in mass and redshift, so the widely used decomposition
method with constant circularity cuts is oversimplified and underestimates thin
disc at JWST redshifts. The energy threshold between the stellar halo and the
inner galaxy is also a function of mass and redshift, minimizing at the
sub-Galactic halo mass, where the circularity threshold peaks. Revisiting the
issue of galaxy size predictor, we show that disc sizes in TNG50 exhibit
correlations with three structural parameters besides 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 $c$ that is well described by $r_{1/2}/R_{rm vir}
propto c^{-0.7}$ even when $c$ is measured in the DM only run; 3) more
actively accreting haloes having slightly larger discs, as well as more
significant stellar haloes and lower thin-to-thick ratio. 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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