Angular momentum evolution can be predicted from cosmological initial conditions
With A. Pontzen & H. V. Peiris — arXiv:2012.02201

The origin of angular momentum
- Galaxies → origin of rotational support?
- Physics → origin of vector quantity irrotational field?
- Cosmology → origin of spin alignment signal?

New-Horizon simulation — Dubois+20

Tempel+13
Focus on closed systems: Lagrangian patch
Predict one value for L
Focus on open systems: dark matter haloes
Predict p(L)
Tidal Torque Theory
& semi-Analytical Models

L=a2D˙L0

White 84, Codis+15
Vitvitska+02



AM can be predicted
AM is stochastic/chaotic
TTT
Focus on closed systems: Lagrangian patch
Predict one value for L
sAMs
Focus on open systems: dark matter haloes
Predict p(L)
TTT & semi-analytical models
AM can be predicted from the initial conditions
AM is stochastic/chaotic
Is AM chaotic or not?
Is AM chaotic or not?
Not chaotic if for a given region,
L(t)=f(t)×L0,(1+ϵ),
with f indep. of L0.
Is AM chaotic or not?
Not chaotic if for a given region,
L(t)=f(t)×L0,(1+ϵ),
with f indep. of L0.
Is AM chaotic or not?








How to change L0 all other things being equal?
ΛCDM gives you =L0 … all other things different.
*Only an illustration, ICs do not correspond to the halos below.



N-body numerical integration


N-body numerical integration




+
Original L0
Genetic modif.
N-body numerical integration
Contrast x50
Roth+15, Stopyra+20
Can compute
P(δδ(x)=v)
or
P(δi∑αiδi=v)
or
P(δLx=v)
+ minimization of Δχ2
⇒ unique solution
= "genetically modified density field"




+
=
Original L0
Genetic modif.
New initial L0′
N-body numerical integration

N-body numerical integration
Same region & environment
Different L0
Contrast x50
Roth+15, Stopyra+20



Original L0

New initial L0′








Original L

New initial L′





We can predict/control AM down to z=0.*
How does it compare to predictions from linear theory?
*AM of regions, not halos
Prediction from linear theory:
Lpred.=timea2D˙×spaceL0.
Simulations with genetically modified initial conditions
Lpred.=timef(t)×spaceL0,
where f(t) is the measured growth rate of a given region in the ref. simu.
Comparison with tidal torque theory
Prediction from linear theory:
Lpred.=timea2D˙×spaceL0.
Simulations with genetically modified initial conditions
Lpred.=timef(t)×spaceL0,where f(t) is the measured growth rate of a given region in the ref. simu.
Comparison with tidal torque theory
Comparison with tidal torque theory
Median of deviations
Prediction from linear theory:
Lpred.=timea2D˙×spaceL0.
Simulations with genetically modified initial conditions
Lpred.=timef(t)×spaceL0,where f(t) is the measured growth rate of a given region in the ref. simu.
Comparison with tidal torque theory
Median of deviations
Scatter of deviations
Prediction from linear theory:
Lpred.=timea2D˙×spaceL0.
Simulations with genetically modified initial conditions
Lpred.=timef(t)×spaceL0,where f(t) is the measured growth rate of a given region in the ref. simu.
Comparison with tidal torque theory
Median of deviations
Scatter of deviations
- Much more accurate pred. than linear theory
- Departure happen at later time
- The smaller the modif., the smaller the scatter
⇒ linear response
Conclusions
Explored how L of given fixed regions changes with changed L0
- angular momentum can be predicted accurately from initial conditions (not chaotic)
- possible to improve linear theory by predicting growth rate f(t)
- apparent stochasticity of AM of halos ⇒ result of particle membership
Read more in Cadiou, Pontzen & Peiris arXiv:2012.02201.
Conclusions
What's next?
- apply to baryons instead of DM only?
- extend analysis to halos?
- predict f(t) rather than measure it?
Read more in Cadiou, Pontzen & Peiris arXiv:2012.02201.
Explored how L of given fixed regions changes with changed L0
- angular momentum can be predicted accurately from initial conditions (not chaotic)
- possible to improve linear theory by predicting growth rate f(t)
- apparent stochasticity of AM of halos ⇒ result of particle membership
AM genetic modifications
Initial L given in initial conditions by
Lz,0∝i,j,k∑[(qxijk−qˉx)∇yϕijk−(qyijk−qˉy)∇xϕijk].
Genetic modifications: find u such that
u⋅δ=L0,
with δ={δi0j0k0,…,δinjnkn} and solve for
u⋅δ′=L0′
with minimal change.
deck
By Corentin Cadiou
deck
- 266