Corentin Cadiou
cadiou@iap.fr

Researcher @ CNRS (France)

https://github.com/cphyc/

Tracing Cosmic Evolution:

From the CMB to the Web, the CGM, and Galactic Disks

kpc

100 kpc

Mpc

Gravitational
collapse

Baryonic physics, star form, AGNs

Feedback processes

Perturbations

Simulations

Perturbation
theory

Galaxy formation in a 🥜 shell

Dark matter (DM) halo formation
Gas condenses in DM halo
Stars form out of gas
Supernova + AGNs reinject energy

T [K]

Cooling rate \(\Lambda\)

\(\dfrac{\mathrm{d}T}{\mathrm{d}t} = \Lambda(T) \rho^2\)

\(\dfrac{\mathrm{d}M_\star}{\mathrm{d}t}\propto \rho^{3/2}\)

increasingly non-linear

Accretion shocks, adiabatic heating, KH instabilities etc.

Vallés-Pérez+24

Galaxy formation in a 🥜 shell

Dark matter (DM)
Gas condenses in DM potential
Stars form out of gas
Supernova + AGNs reinject energy

increasingly non-linear

increasingly chaotic?

⇒

Intrinsic alignment measurement: Ganeshaiah Veena+ 19 · Alignment: M. Sachs

Neighbouring galaxies' shapes are aligned
(on the plane of the sky)

Intrinsic alignment

Baryon dominated?
No cosmo information?

Weak lensing

L.o.s. measurement of
dark matter density

⇒

Galaxy formation: the biased point of view of the spin

Stochastic spin: Vitviska+ 02, Beson+ 20
Spin prediction, Porciani+ 02

Spin: \[\lambda = \dfrac{j}{\sqrt{2}R_\mathrm{vir}V_{vir}}\]

Spin jumps at mergers
Distribution well reproduced by drawing mergers' parameters randomly
Theoretical predictions are, at best, inaccurate

First complication

\(\pm 100\%\)!

“Mergers bring chaos”

Second complication

Let's be optimistic and assume we can predict DM spin

DM spin is not even a good predictor for the galaxy's!

Jiang+ 19

\(\lambda_\mathrm{DM}\)

Butterfly effect: Genel+ 19, see also Thiébaut+ 08

Third complication

Resimulating the same galaxy twice yields different results ⇒ galaxies are chaotic

Is DM angular momentum chaotic?

Results from Cadiou+21, 22

1 Is DM angular momentum chaotic?

Results from Cadiou+21, 22

1

DM angular momentum

\(z=0\)

\( z = 100\)

\(z=0\)

\( z = 100\)

[White 84]

DM angular momentum

\(z=0\)

\( z = 100\)

[Genetic modifications: Roth+16, see also Rey&Pontzen 18, Stopyra+20]

DM angular momentum

Time

Angular
momentum

DM angular momentum

✅ AM of fixed DM regions responds ~linearly (so is not chaotic!)

However, particle membership hence DM halo does not

Angular
momentum

Time

DM angular momentum

Dark matter spin is hard to predict

the usual culprit are mergers

Are mergers really
stochastic?

Results from Cadiou +24b

2

Cadiou+24
Based on the critical event theory (Cadiou +20)
itself based on Hanami 2001

We can make some reasonable predictions
of orbital spin of mergers

Given: tides + density peaks

\(z\gg 100\)

\(z = 0\)

Changes to tides at \(z=100\), effect at \(z<1\)

How chaotic is baryonic
angular momentum?

Results from Cadiou +21a

3 How chaotic is baryonic
angular momentum?

Results from Cadiou +21a

3

\(\lambda_\mathrm{DM}\)

Full hydro simulations
(RAMSES, New-Horizon model):

Resolved disk height
\(\Delta x_\mathrm{min} = 35\ \mathrm{pc}\)
\(M_\mathrm{200c} = 10^{12}\ \mathrm{M}_\odot\)
at \(z=2\)
SF, AGN, SN feedback
3 galaxies, 5× scenario each

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

\( j_0 \times 1.2\)

\( j_0 \times 1.5\)

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

\( j_0 \times 1.2\)

\( j_0 \times 1.5\)

See Cadiou+21a

INPUT: Changes to tides \(z=\infty\)

OUTPUT: Ang. mom
\(z=2\)

Halo and disk evolve separately,

this allows stellar AM to be ~linear despite halo AM not being

Gas + stars spAM

Stars spAM

Halo spAM

See Cadiou+21a

Special case: no massive satellite

Low tides

High tides

\(\mathcal{B}\searrow\)

\(R_\mathrm{eff} \nearrow \)

\(v/\sigma\nearrow\)

See Cadiou+21a

Impact of the cosmological-scale tides on halo properties

Results from Storck, Cadiou+25

4

Impact of the cosmological-scale tides on halo properties

Results from Storck, Cadiou+25

4

\(\rho_\mathrm{i}, v_\mathrm{i}\)

\(\Lambda\)CDM+baryon non-linear evolution

halo & galaxy properties

What if the galaxy had formed here instead?

or here?

The “splicing” technique

Generate ICs
Integrate (\(N\)-body)
Select region of interest
Trace back to ICs
“Splice” the region
Integrate again

\(t\)

Splicing: equivalent of constraining density field at all points in region

\(\longleftarrow 50\,\mathrm{Mpc} \longrightarrow\)

Same halo (same initial tides + density)

forming closer and closer to filament

Repeat for 5 halos, 9 positions

\(\sigma\)

\(\langle q\rangle\)

Deviation from the mean

For different quantities

spin alignment

shape alignment

\(\sigma\)

\(\langle q\rangle\)

Angular momentum transport: CGM structure

Results from Cadiou+25
(& Rey+CC+25 — Katz+CC+25 — Storck+CC+25 — Choustikov+CC+25)
See also CC+22 — Kocjan+CC+24,

5

kpc

100 kpc

Mpc

Gravitational
collapse

Baryonic physics, star form, AGNs

Feedback processes

Perturbations

Simulations

Perturbation
theory

Simple isothermal CGM vs. Complex multiphase CGM

Well-mixed (isothermal)
"Bathtub" modelling

Not well-mixed (turbulence)
How much gas reaches the galaxy?

Megatron simulations:
high-\(z\) galaxy
+ non-equilibrium chemistry
+ radiative transport
+ \(\sim 50-100\,\mathrm{pc}\) resolution

Complex, multiphase structure,
Smallest structures at resolution limit,
Non-equilibrium ionized structures
- impact on thermochemical structure,
- impact on observations.

Megatron simulations:
high-\(z\) galaxy
+ non-equilibrium chemistry
+ radiative transport
+ \(\sim 50-100\,\mathrm{pc}\) resolution

Complex, multiphase structure,
Smallest structures at resolution limit,
Non-equilibrium ionized structures
- impact on thermochemical structure,
- impact on observations.

Increase of resolution:
⇒ more small scale structures

Megatron simulations:
high-\(z\) galaxy
+ non-equilibrium chemistry
+ radiative transport
+ \(\sim 50-100\,\mathrm{pc}\) resolution

Complex, multiphase structure,
Smallest structures at resolution limit,
Non-equilibrium ionized structures
- impact on thermochemical structure,
- impact on observations.

OIII column density
in simulation

assuming ionization equilibrium

\(40\,\%\)-change in HI covering fraction

Conclusions

Tides set merger orbital parameters & angular momentum accretion
Mergers are not stochastic/not rerolling the dice
Trickling down to galactic scale, which drives scaling relations
Galaxies are less stochastic than expected
Galaxy & DM spin are partially independent at the level of individual galaxies
Non-linear effects on halo shape and alignment are comparable to population-level
Crucial to investigate further for the success of Euclid or LSST
Knowledge/modelling frontier: Circum Galactic Medium transport
Non-equilibrium, multiphase state in obs. (low-\(z\)) and sims (high-\(z\))
Cosmic web → CGM → ISM: how does AM evolve in this picture?