Corentin Cadiou
CNRS Researcher

NAM | 08/07/25

How the Large-Scale Environment Impacts Galaxy Evolution

Left: Leclercq+17
Right: Galárraga-Espinosa+23
Bottom left: Ramsøy+21

Cosmic web: a multiscale structure
 

From Mpc scales
all the way to galactic scales

Cosmic web: effects on scalar halo properties
 

Biasing of possible formation histories:

Late formation & high accretion rate (for high-mass halos)
Early formation & low accretion rate (for low-mass halos)
in filament compared to field

Left: Musso, CC+18
Right: Kraljic, ..., CC+18

See also Tojeiro+16, ...

High mass                                    Low mass
 


Late form.             Early form

High-mass scenario

Cosmic web: effects on scalar galaxy properties
 

Close to cosmic web: redder, lower sSFR, smaller \(v/\sigma\)

Left: Kraljic,...CC+18 (GAMA)
Right: Laigle+18 (COSMOS)

Additional baryon-specific effects in the cosmic web:

- feedback &
- accretion

Cosmic web: effects on vector properties
 

Small \(\perp\) alignment of halo spin/shape with filament 

Left: Codis+18
Right: Ganeshaiah Veena+18

See e.g. Tempel+13 for measurement in observation

\(\perp\) filament

// filament

Cosmic web: effects on vector properties
 

How can we study this?

Sample \(M\) at fixed cosmic web
or sample cosmic web at fixed \(M\)

Storck, CC+25 / Bot. right: Aragon-Calvo 15

Cosmic web: effects on vector properties
 

Small \(\perp\) alignment of halo spin with filament 

Constrained simulations: CC+22

Environment perturbed on \(>\mathrm{Mpc}\) scales

Cosmic-web-scale information trickles to galactic scale \(\Rightarrow\) what's the messenger?

The local cosmic web \(<1\,\mathrm{Mpc}\): observations
 

First (?) measurement of the local cosmic web in observations

\(M_\star=10^{9}-10^{12}M_\odot\); miniJPAS and DESI: Galárraga-Espinosa+25

\(3\,\mathrm{Mpc}\)

\(\sim1/3\,R_\mathrm{vir}\)

The local cosmic web \(<1\,\mathrm{Mpc}\): theory

 

2-3 “Cold flows” embedded in local cosmic web pancakes, feeding the galaxy

\(z=2.5, M_\star = 10^{12}\,M_\odot\); Danovich+12

The CGM cosmic web \(\lessapprox 100\,\mathrm{kpc}\): observations


Hints of detection of anisotropic extended cold emission

Excess of Ly\(\alpha\) in stacked images
\(3< z< 4\); Gallego+18

Ly\(\alpha\) radiation between quasar pairs; \( z\sim 3\); Herwig+24

Ly\(\alpha\), CIV and HeII emissions; Vayner+23

The CGM cosmic web \(\lessapprox 100\,\mathrm{kpc}\): theory

 

Ly\(\alpha\), OIII] \(\lambda\lambda 1663\mathrm{Å}\), HeII \(\mathrm{\lambda} \mathrm{1640Å}\), ...: tracers of the CGM-cosmic web connection?

Simulated \(n_\mathrm{OIII}\), Megatron; \(z=4\); CC in prep

Mitchell, ... CC+20

The CGM cosmic web \(\lessapprox100\,\mathrm{kpc}\): theory

 

Survival and observability of cold flows

Aung+24, see also Mandelker+16,19; Padnos+18; Cornuault+18

Connecting the cosmic web through the CGM

 

Effect of \(>\mathrm{Mpc}\) scale CW on galaxy quite clear now

 

How this manifest much less so. Theoretical uncertainties
remain on small-scale:

  • Effect of feedback/AGNs on CW?
  • Survival of cold flows?
  • Observational predictions?
  • Deblend from outflows?
     

Prospects of observation of cosmic web/CGM interface:

  • VLT/BlueMUSE: \(z\sim 2-4\) (Ly\(\alpha\), CIV)
  • ELT/Harmoni: \(z>3\) (Lyα, CIV, HeII, Hβ)
  • ALMA: \(z\sim 2-4\) ([CII]158µm)

 

Corentin Cadiou — cadiou@iap.fr

Ramsøy+21

Lu+24

Same halo (same initial tides + density)

forming closer and closer to filament

Repeat for 5 halos, 9 positions

Deviation from the mean

For different quantities

spin alignment

shape alignment

Slide #2: Relate large-scale filamentary structure to small scale accretion (Danovich)

 

Magic number: #3 filaments

Kraljic+20

Magic number: 3 filaments

← satellites, Garaldi+18

Danovich+12, gas →

Slide #3: Where cosmological accretion meets the CGM

Mention work by Dekel et al. cold flows paradigm

Pinpoint in mass/time.

Danovich+12

Kocjan+24

Slide #4: Observational evidences of these flows connecting to the web?

Gallego+18→ stacking of Ly-\(\alpha\)

Vayner+23 → Direct emission in Ly-\(\alpha\) and HeII

Slide #4: What happens to the gas in there?

Kocjan+, Danovich+, Prieto+

Mitchell+20: most of the Ly\(\alpha\) escaping-photons come from first-infall

Stewart+17

Cold-accreted gas has an excess of similar rotation

Cadiou+21
Torque are dominated by gravity

[Danovich+15]

I. Torque with cosmic web

II. Transport at constant AM

III. Torque down in inner halo

IV. Mixing in inner disk & bulge

Dark matter
\(80\%\) of mass

Gas
\(20\%\) of mass (initially)

Stars
\(<1\%\) of mass

Galaxy formation

  1. Dark matter (DM)
  2. Gas condenses in DM potential
  3. Stars form out of gas
  4. Supernova reinject energy

T [K]

Cooling rate \(\Lambda\)

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

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

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

But are galaxies truly chaotic?

How complex are galaxies?

Results from Cadiou+ 24a

1

How complex are galaxies?

Results from Cadiou+ 24a

1

Example of the S-curve:

2D manifold embedded in 3D

Compute \(k\)-nearest neighbors
→ edges of a graph

Draw a point
→ find shortest path to all others

Take a radius
count number of points, \(p\) within \([r, r+\mathrm{d} r]\)

\(\Rightarrow p(r) \propto r^{D-1}\)

\(r\)

\(\#(<r)\)

Actually \(p(r)\propto \sin^{D-1}(r)\), Granata & Carnevalle 16

\(\#(<r)\)

COSMOS dataset

300,000 observed galaxies

Horizon-AGN

700,000 simulated galaxies

We have a method to measure
the intrinsic dimensionality of any dataset.

  • Magnitude measurements (not images!)
  • 14 photometric wide-bands (u*, g, r, i, z, y, Y, J, H, Ks, B, V, IRAC CH1 & CH2)
    + 14 narrow-bands
  • SNR > 2
  • passive/active selection

Note: we are not working with images, but integrated magnitudes

COSMOS dataset

300,000 observed galaxies

Horizon-AGN

700,000 simulated galaxies

No more than \(\sim 4\) independent parameters? (with comparable magnitudes)

See Disney 08 for even more controversial results, although with smaller statistics

Horizon-AGN

700,000 simulated galaxies

No more than \(\sim 3\) independent parameters!

Galaxy formation is tightly constrained

Galaxies populate a 3D attractor?

\(M\)

\(z\)

\(j\)

With simulated noise

Without simulated noise

Is DM angular momentum chaotic?

Results from Cadiou+21, 22

2

Is DM angular momentum chaotic?

Results from Cadiou+21, 22

2

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

3

Based on the critical event theory (Cadiou +20)

We can make some reasonable predictions
of orbital spin of mergers

Given: tides + density peaks

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

tides ×0.5 ⇒ merger @ \(z=0.7\)

tides ×1.1 ⇒ merger @ \(z=0.55\)

tides ×1.2 ⇒ merger @ \(z=0.5\)

tides ×2 ⇒ merger @ \(z=0.2\)

How chaotic is baryonic
angular momentum?

Results from Cadiou +21a

4

How chaotic is baryonic
angular momentum?

Results from Cadiou +21a

4

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

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

\( j_0 \times 1.2\)

\( j_0 \times 1.5\)

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

\( j_0 \times 1.2\)

\( j_0 \times 1.5\)

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

See Cadiou+21a

INPUT: Changes to tides  \(z=\infty\)

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

\( j_0 \times 0.66\)

\( j_0 \times 0.8\)

\( j_0 \times 1.2\)

\( j_0 \times 1.5\)

\( j_0 \times 0.8\)

See Cadiou+21a

INPUT: Changes to tides  \(z=\infty\)

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

Stellar angular momentum responds ~linearly
to large-scale tides

Impact of the cosmological-scale tides on halo properties

Results from Storck, Cadiou+25

5

Impact of the cosmological-scale tides on halo properties

Results from Storck, Cadiou+25

5

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

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

halo & galaxy properties

What if the galaxy had formed here instead?

What if the galaxy had formed here instead?

or here?

The “splicing” technique

  1. Generate ICs
  2. Integrate (\(N\)-body)
  3. Select region of interest
  4. Trace back to ICs
  5. “Splice” the region
  6. Integrate again

\(t\)

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

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

-

-

Conclusions

The title might have been clickbait… but

  1. On global scales galaxies aren't that complex: success of simulations
    Actual complexity is on the order of 3 (mass, redshift, SFR?)
     
  2. Tides determine merger orbital parameters & angular momentum accretion
    Mergers are not stochastic/not rerolling the dice
     
  3. 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
     
  4. Non-linear effects on halo shape and alignment are comparable to population-level
    Crucial to investigate further the success of Euclid or LSST

Are galaxies chaotic?