simulating the universe · gadget3 – large scale force with fourier convolution and particle mesh...

Romain TeyssierBeyond LCDM, Oslo 2015

Simulating the Universe

Christine Corbett Moran, Irshad Mohammed, Manuel Rabold,

Davide Martizzi, Doug Potter, Aurel Schneider

Oliver Hahn, Ben Moore, Joachim Stadel


Outline

- N-body codes: where do we stand ?

- accuracy

- new solvers ?

- Challenges in Modified Gravity calculations.

- f(R) and MOND

- predictions

- Simulating baryonic effects.

- feedback processes

- the physics of clusters & groups

- baryons as a nuisance


EUCLID requires 1% accuracy up to k=10 h/Mpc in the theory.

Different codes have different systematic effects (time integration).

GADGET3

– large scale force with Fourier convolution and Particle Mesh

– small scale force with tree code (multipole direct space convolution)

PKDGRAV3

– large and small scale force with (fast multipole) tree code

– periodic BC using Ewald summation (use of GPU acceleration)

RAMSES

– Particle Mesh with Adaptive Mesh Refinement

– Direct Poisson solver with Multigrid acceleration

Ongoing Euclid CosmoSim WG project

identical GADGET initial conditions and output files

code comparison beyond the 1% barrier

N body simulations: the state of affairs


Schneider et al. 2015 in prep.

Systematic effects in N body codes

linear non-linear


Schneider et al. 2015 in prep.

Heitmann et al. 2014

Comparing to the Cosmic Emulator


Comparing to the Cosmic Emulator

Dark Sky simulation (Skillman et al. 2014)


Beyond N body codes ? The Vlasov approachHahn & Angulo (2015), Hahn, Abel, Kaehler (2013)


Cosmological simulations with modified gravity

Viable models show small deviations (1-10%) with LCDM.

Motivated theoretically by dark matter (e.g MOND) or dark energy (e.g. f(R)).

A fully developed theory is required with at least:

– time evolution of the expansion factor (homogeneous universe)

– self-consistent initial random fluctuations

– viable weak-field limit for the dynamics of the matter

MOND (AQUAL): a non-linear Poisson equation

f(R) model: a non-linear Poisson equation and a standard linear Poisson solver

MOND (QUMOND): 2 standard (linear) Poisson equations


Cosmological simulations with modified gravity

Challenges for simulations with modified gravity models

– direct or Fourier convolution approach not valid anymore

– non-linear field solvers are slow and converge poorly

– non-linear multigrid techniques; Raphson-Newton iterations

MLAPM with f(R) solver on AMR (Zhao, Li, Koyama 2011)

ECOSMOG: f(R) field solver for the AMR code RAMSES (Li et al. 2012)

MG-GADGET: f(R) models for the GADGET code (Puchwein et al. 2013)

Phantom of RAMSES: QuMOND for the RAMSES code (Lüghausen et al. 2014)

RAyMOND: AQUAL (and QuMOND) for the RAMSES code (Candlish et al. 2015)

…


Lombriser et al. 2012

Simulations with f(R) modified gravity model


Simulations with f(R) modified gravity model

Zhao, Li & Koyama (2011)


Corbett strong (F4) medium (F5) weak (F6) ΛCDMz

Corbett Moran et al. 2014

Zoom simulations with f(R) model


Zoom-in simulations with f(R) models

Corbett et al. (2014)


Very low efficiency of gas conversion into star.

Small mass galaxies are dominated by stellar feedback.

Large mass galaxies are governed by AGN feedback.

“Baryonic effects are too difficult to model” (18%)

Moster et al. (2010)

Dekel & Silk (1986) Silk & Rees (1998)

Stellar-to-halo mass ratio


Dark matter cusp-to-core transformation

Excellent fit of the dark matter profile with a pseudo-isothermal profile

de Blok et al. (2001)


Galaxy formation in groups and clusters


Adiabatic hydrodynamics: 10% accuracy ?

Rabold et al. in prep.


Feedback models from SMBH in massive ellipticals

- Thermal feedback (Sijacki et al. 2007; Booth & Schaye 2010; Teyssier et al. 2010): “thermal bombs”

- Radiative feedback (Choi et al, 2012, 2014; Vogelsberger et al. 2013): dust-absorbed UV radiation from the accretion disk.

- Jet feedback (Omma et al., Cattaneo & Teyssier, Dubois et al. 2010, Choi et al. 2014): injection of momentum in a jet-like geometry.

- Cosmic ray feedback (Pfrommer at al. 2010; Oh et al, 2013): heating from Alfven waves excited by CR-induced instabilities.

- Bubble feedback (Sijacki et al. 2007): buoyantly rising bubble with initial radius close to 50 kpc

These models are related to the quasar mode (thermal, radiative) or to the radio mode (jet, CR, bubbles) of AGNs.

Cosmological simulations with zoom-in or periodic boxes and around 1 kpc resolution.


The effect of baryons on the halo mass

Martizzi et al. 14 Martizzi et al. 14

RAMSES code


Martizzi+14

Central galaxy stellar mass


Central galaxy stellar mass distribution

Martizzi et al.14 Kravtsov et al.14


The effect of baryons on the halo mass

Vogelsberger et al. 14 Genel et al. 14

AREPO code


Analytical halo model for the matter power spectrum

For each halo, we consider analytical models for each of the 3 components: gas, dark matter and the central galaxy

Using simple analytical profiles, we apply the “halo model” methodology to compute the power spectrum. Main ingredients are:

- mass of the central galaxy : abundance matching

- size of the central galaxy : 0.015 of the viral radius

- total gas mass versus total halo mass : free parameter

- adiabatic contraction for CDM

Good agreement with the zoom-in simulations of Martizzi et al. (2014)

White (2004), Zhan & Knox (2004), Rudd et al. (2008), Guillet et al. (2010), Semboloni et al. (2011), van Daalen et al. (2011)…


A simple model for the effect of AGN feedback

Mohammed et al. (2015)Semboloni et al. (2011)


A simple model for the effect of AGN feedback


Cosmological parameters estimation

Mohammed et al. (2015)

Mock weak-lensing observation with 3 redshift bins (EUCLID-like)

increase max. multipole


Beating down baryonic effects ?

Mohammed et al. (2015)


Conclusions

- N-body codes are 1% accurate below k=1 Mpc/h; 5% accurate between 1 and 10 Mpc/h. Do we need higher-order accurate N-body solvers ? Something else ?

- Modified gravity solvers are getting more and more popular. Still slow and fragile.

- Simulations with baryons are not even 10% accurate !

- Massive variations between codes and feedback models !

- AGN feedback models (when properly calibrated) can reproduce reasonably well the main properties of groups and clusters.

- The effect of baryons reaches 10% (deficit) at k=20 Mpc/h. More ?

- Cosmological parameters could in principle be fitted with 1% accuracy down to 1 arcmin if one uses an unbiased model.

simulating the universe · gadget3 – large scale force with fourier convolution and particle mesh...

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