Corentin Cadiou
CNRS Researcher

Filaments @ Kavli IPMU | 2026

What flows from the cosmic web into galaxies?

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

Cosmic web: a multiscale structure  

Mpc to galactic scales

Right: Peng+10 · Related: Peng+12 · Left: Zooniverse

“Environmental” quenching  

Higher density | high mass \(\rightarrow\) redder galaxies


⚠️ cannot explain morphology/orientations!

Cluster-like

Void-like

Right: Peng+10 · Left: Romanowsky & Fall 12

“Environmental” quenching  

Higher density | high mass \(\rightarrow\) redder galaxies


⚠️ cannot explain angular momentum!

Cluster-like

Void-like

Related: Cadiou+22 (controlled stellar AM)

Cosmic web: effects on scalar galaxy properties

Distance to filament changes

  • color & sSFR
  • rotational support (\(v/\sigma\))
Left: Laigle+18 (COSMOS)
Right: Kraljic, … CC+19 (Horizon-AGN)
See also: Kraljic, … CC+18 (GAMA)

Triple effect:

  • Halo assembly bias
  • Feedback
  • Accretion

Cosmic web: effects on halo vector properties  

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

Figures: Codis+18 · Ganeshaiah Veena+18 · Related: Codis+12 · Obs.: Tempel & Libeskind 13

\(\perp\) filament

// filament

Interim takeaway 1/3   Cosmic web drives 1%-level effects?

Cosmic web: effects on halo vector properties  

How can we study this?

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

Storck, CC+25 · Aragón-Calvo 16 · Splicing: CC+21

\( \pm 20\% \)!

Interim takeaway 2/3   Local cosmic web drives 20%-level effects (DM halos)

More in Anatole Storck’s Thursday talk

Cosmic web: effects on galactic vector properties  

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

Experiment: CC+22a · Gas torques: CC+22b · Related: Danovich+15

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

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

Interim takeaway 3/3   Local cosmic web drives 20%-level effects (galaxies)

How strongly does the cosmic web affect galaxy formation?

\(\ll 1\%\) or \(\gg 20\%\)?

How strongly does the cosmic web affect galaxy formation?
\(\ll 1\%\) or \(\gg 20\%\)?

Sabri Errachdi
PhD work in progress
More in his Wednesday talk

Related methods: Aragón-Calvo 16 · Storck, CC+25

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

Related: Dekel+09 · Danovich+15 · Ramsøy+21

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

Related (Mpc scales): Bacon+21
Accretion interpretations: Zhang+23 · Johnson+22
CGM emission: how far can we see?
R = radius from galaxy · L = total span / filament length · selected systems and stacks
ObservableInstrument / sampleProjected reach [physical kpc]Selected references
Lyα — individualMUSE: QSO pairs / overdensitiesRₜ ≈ 110; L ≈ 700–1000Tornotti+25a, 25b
Lyα — stacksMUSE / HETDEX: LAEsR ≈ 60–160Guo+24; Lujan Niemeyer+22
C IV, He II, C III]Quasar nebulae / stacksR ≈ 45 (stack); ≈100 (individual)Guo+20; Zhang+23
[O II]MUSE: quasar + filamentR ≈ 50; filament L ≈ 120Johnson+22
[O III]JWST: quasar / starburstR ≈ 60; L ≈ 100Peng+25
Balmer / optical linesKCWI nearby; JWST z ≈ 6 QSOsR ≈ 30; Hα R ≈ 4–11+Nielsen+24; Ďurovčíková+25
Mg IIMUSE: galaxy groupL ≈ 70Leclercq+22
[C I] / COALMA (+ACA): radio galaxy / QSOL ≈ 100Emonts+23; Li+21
[C II] 158 μmALMA: z ≈ 5–7 galaxies∼10-kpc-scale haloesFujimoto+19; Posses+25
O VIHST: starburstR ≈ 23Hayes+16
Diffuse X-rayseROSITA: massive-galaxy stacksR ≈ R₅₀₀cZhang+25
PAHs / warm dustJWST: Makani windR ≈ 35Veilleux+25
Rₜ denotes the CGM–IGM transition. Emission morphology alone does not establish inflow.
From ionised filaments to cold gas
Three complementary views · projected physical scales
Lyα · MUSE
Tornotti+25 · Fig. 1

Tornotti+25 · \(z\simeq3.2\)

\(L \approx 700\,\mathrm{kpc}\)

CGM–IGM transition: \(R \approx 100\,\mathrm{kpc}\)

[O III] · JWST
Peng+25 · Fig. 2

Peng+25 · \(z=2.8\)

\(L \approx 100\,\mathrm{kpc}\)

Enriched filaments; feedback
[C I] · ALMA
Emonts+23 · NRAO composite

Emonts+23 · \(z=3.8\)

Stream \(L \approx 100\,\mathrm{kpc}\)

Cold-gas stream; inflow candidate
Related accretion diagnostics: Zhang+23 · Johnson+22

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


Ly\(\alpha\) is great, but hard to interpret
Other lines are great… but are we getting the right predictions?

Movies / NEq: CC+26
Lyα: Mitchell, … CC+21
Related NEq: Segers+17

Ly\(\alpha\)

H\(\alpha\) recomb. only

CIII] 1906Å

[CIV] 1548Å

HeII 1640Å

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


Ly\(\alpha\) is great, but hard to interpret
Other lines are great… but are we getting the right predictions?

Movies: CC+26 · Lyα: Mitchell, … CC+21 · Related NEq: Segers+17

H\(\alpha\)

HeII 1640Å

Ly\(\alpha\)

Interim takeaway   Predictions and interpretation of CGM observations may not yet be mature.

[CIV] 1548Å

CIII] 1906Å

Connecting the cosmic web through the CGM

The effects of the cosmic web on galaxies at \(>\mathrm{Mpc}\) scales are well established,
but likely massively underestimated.

How these effects reach galaxies is less clear.
Uncertainties remain on small scales:

  • Effects of feedback and AGN on the cosmic web
  • Survival of cold flows
  • Observational predictions
  • Separating inflows from outflows

Observing the 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

Context: CC+22a · CC+26 · Faucher-Giguère & Oh 23