*chto@uchicago.edu

Deciphering baryonic feedback: Multiprobe analyses of clusters and weak lensing

Chun-Hao To*

I also work on...

Lensing around dwarf galaxies

Pixel-level Synergies between Roman and Rubin

Galaxy Cluster physics 

Dark Matter Halo

~

5\times 10^{14} M_\odot

Red galaxies

~ 2% of the mass

Hot gas

~ 10% of the mass

Cosmology

Galaxy physics

Baryonic feedback

Yang+03, Lin&Mohr04, More+16,
Kravstov+18, Shin+19, To+20 (APJ 897,15), ... many more

Vikhlinin+06, Eckert+16,
To+24 (JCAP 2024, 037), Dalal+26, Kovac+25, Siegel+25, ...many more

Bahcall 95, Wang&Steinhardt 98,  Borgani+ 01, Allen+ 03, Vikhlinin+ 09, DeHann+16, To+ 21, Bocquet+24, Ghirardini+ 24, DES+25, ... many more

Galaxy Cluster physics 

Hot gas

~ 10% of the mass

  • Millimeter wave (Sunyaev-Zel'dovich effect)

 

 

 

 

  • X-ray

 

 

 

 

 

\frac{\Delta T_{tsz}}{T_{CMB}} \propto \int n_e T_e d\ell
S_X \propto \int_{\sim 0.5\ KeV}^{\sim 2\ KeV} n_e n_H \Lambda(T,E) dE

Line of sight

Cooling function

\frac{\Delta T_{ksz}}{T_{CMB}} \propto \int n_e v_{e, los} d\ell

Why should we care?

To+24,  see also Lucie-Smith+ 25

  • Significant information in cosmic shear is lost due to uncertain baryonic physics.
\xi_+
\xi_-

Why should we care?

To+24,  see also Lucie-Smith+ 25

  • Significant information in cosmic shear is lost due to uncertain baryonic physics.
     
  • Lots of this small-scale information comes from galaxy clusters.

What are the observables

Weak lensing 

CMB

Y_{SZ} \times 10^{-4}
\langle M|Y_{SZ} \rangle (10^{14} M_\odot)

What are the observables

Y_{SZ} \times 10^{-4}
\langle M|Y_{SZ} \rangle (10^{14} M_\odot)

Change of Matter clustering 

Model

Godmax:
A Schneider-Teyssier-type model with parametrized gas distribution implemented in Jax
(Pandey+ (incl. CT) 24)

 

See also Schneider&Teyssier 15, Giri+ 21, Schneider+ 25, and many more

Godmax halo model 

Pandey+ (incl. CT) 24
 

Halo=

  • Collisionless materials (dark matter + stars):
    NFW profile with a scaled radius obtained via adiabatic contraction.
  • Gas:


     
  • Central galaxy:
    Power law with exponential cutoff
\rho_{gas}=\frac{f_b-f_s(M)}{(1+10\frac{r}{r_{200}})^{\beta(M,z)}(1+(r/\theta_{ej}r_{200})^\gamma)^{\frac{\delta-\beta(M,z)}{\gamma}}}

Gas density to observed signal

\rho_{gas}
P_{total}
P_{total}
P_{thermal}
P_{thermal}
P_{e}
Y (r) \propto \int d\ell \frac{\sigma_T}{m_ec^2}P_e(r)
\frac{P_{nt}}{P_{total}}=\alpha_{nt} f(z) (r/r_{500c})^{\eta_{nt}}

hydrostatic equalibrium 

Nelson+14  (Turbulence, magnetic field)

Electron and protons are in equalibrium 

and molecular mass

Goal

What are the observables

Y_{SZ} \times 10^{-4}
\langle M|Y_{SZ} \rangle (10^{14} M_\odot)

Change of Matter clustering 

Model

Godmax:
A Schneider-Teyssier-type model with parametrized gas distribution implemented in Jax
(Pandey+ (incl. CT) 24)

 

See also Schneider&Teyssier 15, Giri+ 21, Schneider+ 25, and many more

Simulation validation

Text

Measurement

Prediction

+ Godmax model 

To+ 24

Simulations validation

Text

To+ 24

Pathfinder study

Dalal+ (incl. CT) 26

ACT cluster finder

Nemo

Shin+25

Godmax
Model

Noise

Pathfinder study

Dalal+ (incl. CT) 26

Pathfinder study

Dalal+ (incl. CT) 26

We find remarkably consistent results compared to other probes.

Status

  • Lots of data exist and have been used to constrain feedback. Here are a very incomplete list:

    • WL: Ario+22, Anbajagane+25, DES+26, Xu+25.

    • tSZxtSZ: Raghunathan+26, Chaubai+26, Efstathiou&McCarthy25.

    • tSZxothers: Sanchez+22, Dalal, CT+25, Pandey+25.

    • kSZ x others: Hadzhiyska+24, Bigwood+25, Ropper+25, Hotinli, Smith, Ferraro 25.

    • X-ray: Kovac+25, Eckert+25, Siegel+25, Zhang+26.

    • FRB: Reischke & Hazstotz25, Wang+25.

    • QSO absorption: Chen & Zahedy26, Qu+23, 24, Zahedy+19.

Status

  • The modeling landscape: 

    • Baryonification-flavored models that parametrize the gas distribution around halos at a given redshift.
      Schneider+19,25, Arico+20, Anbajagane+24, Osato+23, Williams+23, Semboloni+11,13, Fedeli+14, Debackere+20, Mead+20, Giri+21, Pandey (incl. CT)+24, and many more...
       

    • Hydrodynamic simulations.

      ​McCarthy+17, Schaller+25, Springel+18, Quataert&Hopkins+25, and many, many more... ​

What is missing?

  • Most of the baryon probes involve galaxies. 
    • Clusters rely on galaxies for redshift and selections.
    • kSZ stacks on galaxy samples. 
    • FRB needs to be cross-correlated with galaxies if DM (host) is unknown.
       
  • Weak lensing is sensitive to a broad redshift range.
    • Future weak lensing surveys (such as Roman) will be sensitive to z=0-3. 

Tumlinson+17

Cold gas around galaxies is the fuel of star formation.

Galaxy properties and gas content should be correlated.

What is missing?

We need a model that self-consistently describes galaxy evolution and gas properties across z=0-3. 

Diffsky model

To+ in prep (with diffsky team)

Galaxies:
Jax-based galaxy model

Alarcon+23, Hearin+21

Diffsky model

To+ in prep (with diffsky team)

Galaxies:
Jax-based galaxy model

Godmax:

Jax-based gas model 

Diffbaryon

Alarcon+23, Hearin+21

Diffbaryon model

To+ in prep (with diffsky team)

Preliminary

Hydro simulation

Diffbaryon

Diffbaryon model

To+ in prep (with diffsky team)

Preliminary

Hydro simulation

Diffbaryon

Preliminary

  • Diffbaryon captures                          
     
  • Godmax model underestimates the intrinsic scatter.

Central

P(M_{gas}|M_{halo})
  • Diffbaryon captures                        

https://arxiv.org/pdf/2503.17271

 Sutherland & Dopita (1993).

z= 1, 0.3, 0.1, 0.01

Upenn seminar_05062026

By CHUN-HAO TO

Upenn seminar_05062026

  • 10

More from CHUN-HAO TO