Where do galaxies get their spin from?

A story of angular momentum,

tracer particles and data analysis

z ≥ 2: the puzzle of disk galaxies

Cite paper talking about fast rotator, disruption times, etc.

Mention Danovich, Cold flows

Simulation setup

  • suite of zoom-in simulations (~6), RAMSES (Teyssier 2002)
  • Δx = 35pc, Mstar = 1.1 10⁴ M☉ Mhalo=10¹² M☉
  • Turbulent star formation (Kimm+17, Trebitsch+17)
  • Mechanical feedback (Kimm+15)
  • AGN formation with spin-regulated efficiency (Dubois+12,+14)
  • 30,000,000 tracer particles (~10/cell, 0.5/star, Cadiou+19)

Gas density

Gas tracer density

Filamentary accretion is responsible for most of the mass and angular momentum acquisition (at z>3 ; Kereš+05, Pichon+11, Tillson+12, …)

Filamentary accretion: natural "bridge" between large scale structures (cosmic web) and galaxy formation

3. Contribution to disk formation

1. AM acquisition at large scale

2. Transport along cold flows

Cold gas selection

 

( \( \forall t, T(t)\leq 10⁵\ \mathrm{K} \) and

\( 0.3 R_\mathrm{vir} \leq r(t) \leq 2 R_\mathrm{vir} \))

or

$$ r < 0.3 R_\mathrm{vir} \text{ or } r > 2R_\mathrm{vir} $$

Hot gas selection

 

$$ \exists t, T(t)> 10⁵\ \mathrm{K} \\ 0.3 R_\mathrm{vir} \leq r(t)\leq 2 R_\mathrm{vir} $$

⇒ Defined with Lagrangian history

    + removing accretion from satellites

Kinematics

Kinematics

Cold gas: well aligned down to inner halo

Hot gas: aligned down to inner halo

(Local) dynamics

The (Lagrangian) spAM dynamics is given by

\(\displaystyle \phantom{\frac{\mathrm{d} \mathbf{l}}{\mathrm{d} t}} + \text{gravitational torques} \)

\( \displaystyle \frac{\mathrm{d} \mathbf{l}}{\mathrm{d} t} = \textcolor{darksalmon}{\text{pressure torque}} \)

\(\displaystyle \phantom{\frac{\mathrm{d} \mathbf{l}}{\mathrm{d} t} + } \underbrace{\phantom{\text{gravitational torques}}}_{\text{\textcolor{darkgray}{DM} + \textcolor{orange}{Star} + \textcolor{deepskyblue}{Gas}}} \)

Pressure dominates the ⊥ acceleration in CGM…

locally!

Mean of ⊥ force magnitude

(Global) dynamics

Compute global torque in shell

Dynamics

Locally: pressure dominated...

esp. in the hot phase

... but globally: (DM) gravity dominated

esp. in the cold phase

What is happening?

Test

Time-coherence of torques

Compute \(t_\mathrm{decorr.}\) using Lagrangian history such that

$$ \vec{\tau}(t_\mathrm{decorr.}) \perp \vec{\tau}(0) \color{gray}\qquad\text{ (i.e. } \vec{\tau}(t_\mathrm{decorr.}) \cdot \vec{\tau}(0) = 0)$$

A/ Longer coherence in cold phase (esp. pressure)

Slow decorrelation

Fast decorrelation

Spatial-coherence of torques

Compute sum-of-norm vs norm-of-sum

$$ \dfrac{\left\| \sum_\text{neigh}\tau\right\|}{ \sum_\text{neigh}\left\| \tau\right\|} $$

B/ Pressure: \(\lambda_\mathrm{fluct.}\) is small

Spatial-coherence of torques

Compute sum-of-norm vs norm-of-sum

$$ \dfrac{\left\| \sum_\text{neigh}\tau\right\|}{ \sum_\text{neigh}\left\| \tau\right\|} $$

B/ Pressure: \(\lambda_\mathrm{fluct.}\) is small

Conclusions

Conclusions

Kinematics:

  • AM transported through CGM
  • orientation mostly retained down to outer disk

Dynamics:

  • pressure locally dominant (esp. in hot)
  • gravity globally dominant (esp. in cold)
  • torques have spatial & time variations ⇒ need careful treatment
Test