Description
Dark matter halo formation history correlates strongly with halo concentration,
but it remains unclear if other halo and galaxy properties retain memory of
assembly once halo mass is fixed. We use the large-volume hydrodynamical
FLAMINGO simulation
to investigate this question for a statistically robust sample of 30,665 central haloes
selected in a narrow present-day mass bin centred on $\log_{10}M_{200}/M_\odot(z=0)=13.5$
(bin width 0.3 dex). Haloes are divided into formation-time cohorts using the half-mass
formation redshift $z_{50}$, and we track the median evolution of halo mass growth,
concentration, normalised half-mass radii (dark matter, gas, and stars), and a
dimensionless angular-momentum proxy $\lambda_X \equiv J_X/J_{200}$ as a function of
$\log_{10}(1+z)$.
Despite converging to the same present-day mass by construction, different follow
distinct assembly pathways. Halo concentration shows systematic offsets between early-
and late-forming systems over a broad redshift range, confirming that internal halo
structure retains a strong imprint of formation history. The response of baryonic
properties is more component-dependent: stellar sizes exhibit modest but detectable dependence, whereas gas sizes show weaker and less systematic separation. In
contrast, the spin parameter displays clear cohort-dependent behaviour at
intermediate redshift, with late-forming systems exhibiting systematically higher
normalised angular momentum.
These results demonstrate that halo formation history leaves a measurable imprint on galaxy properties at fixed present-day mass, with the strongest memory preserved
in halo structure and angular momentum, and weaker coupling evident in gas-related size
evolution for this group-scale mass regime.
| I am the presenting author | Yes |
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