The Importance of Subtleties in the Scaling of the 'Terminal Momentum' For Galaxy Formation Simulations
arxiv(2024)
摘要
In galaxy formation simulations, it is increasingly common to represent
supernovae (SNe) at finite resolution (when the Sedov-Taylor phase is
unresolved) via hybrid energy-momentum coupling with some 'terminal momentum'
p_ term (depending weakly on ambient density and metallicity) that
represents unresolved work from an energy-conserving phase. Numerical
implementations can ensure momentum and energy conservation of such methods,
but these require that couplings depend on the surrounding gas velocity field
(radial velocity ⟨ v_r⟩). This raises the question of whether
p_ term should also be velocity-dependent, which we explore analytically
and in simulations. We show that for simple spherical models, the dependence of
p_ term on ⟨ v_r⟩ introduces negligible corrections
beyond those already imposed by energy conservation if ⟨ v_r⟩≥ 0. However, for SNe in some net converging flow (⟨ v_r⟩<0), naively coupling the total momentum when a blastwave reaches the
standard cooling/snowplow phase (or some effective cooling
time/velocity/temperature criterion) leads to enormous p_ term and
potentially pathological behaviors. We propose an alternative Δ-Momentum
formulation which represents the differential SNe effect and show this leads to
opposite behavior of p_ term in this limit. We also consider a more
conservative velocity-independent formulation. Testing in numerical
simulations, these directly translate to large effects on predicted star
formation histories and stellar masses of massive galaxies, explaining
differences between some models and motivating further study in idealized
simulations.
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