Modeling the Physics ofGalaxy Formation

Andrew Benson

California Institute of Technology

Scientific classification Theorist

Scale Galactic – cosmological

Wavelength range Zero – infinity

Favorite color Dark matter

1 March 2011 Modeling the Physics of Galaxy Formation 3

Overview

Questions I'm interested in..... How to build a coherent picture of galaxy

formation From the smallest scales to the largest From low-z to high-z Encompassing widest range of

predictions/observations possible First need a coherent framework for

calculating expectations

Overview | Models | Science | Collaboration

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Advancing Galaxy Formation Codes

Why a new code? Adding in new features (e.g. self-consistent

reionization, noninstantaneous recycling, new star formation rules) to existing models can be challenging

How? Create a code which is modular by design,

isolating assumptions so that they don't have consequences throughout the code.

Overview | Models | Science | Collaboration

GALACTICUS

sites.google.com/site/galacticusmodel

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Design Features

Open source (compiles with GNU compilers) Modular design

Each function can have multiple implementations, selected by input parameter.

“Node” can have arbitrary number of components (e.g. DM halo, disk, spheroid), all with multiple implementations

Combination of smooth (ODE) evolution and instantaneous events (e.g. mergers)

Overview | Models | Science | Collaboration

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Design Features

Well documented Promotes a standard format for merger tree

data www.ctcp.caltech.edu/galacticus/MergerTreeFileFormat.pdf

Parallelized OpenMP MPI (soon...) Currently simple, but allows for expansion

Source codeBinaries

Cloud (Amazon EC2)

Overview | Models | Science | Collaboration

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External Tools

GNU Scientific Library/FGSL ODE solver; integration; other numerics

FoX library Read/write XML files

FSPS Population synthesis

Cloudy Cooling times

Overview | Models | Science | Collaboration

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Modularity

New implementation of function easily added: Write a module containing the function Add directives indicating that this function is for,

e.g., disk star formation timescale calculations Recompile – build system automatically finds

this new module and works out how to compile it into the code

Modules are self-contained and independent Self-initializing and recursive

Overview | Models | Science | Collaboration

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Current Feature List

Components

DM profile [isothermal/NFW]

Hot halo Disk

[exponential] Spheroid

[Hernquist] Black holes

Tracks mass and spin.Spin from mergers and accretion.Accretion spin-up using Benson & Babul formulaJet power from Benson & Babul also.

Tracks mass and spin.Spin from mergers and accretion.Accretion spin-up using Benson & Babul formulaJet power from Benson & Babul also.

Overview | Models | Science | Collaboration

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Physics Monte-Carlo (PCH method)/N-body merger trees CIE atomic cooling Dynamical friction Star formation/feedback Galaxy merging Adiabatic contraction/sizes Chemical enrichment (instant or non-instant)

Current Feature ListOverview | Models | Science | Collaboration

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Current Feature List

Physics (cont.): Disk instabilities Black hole merging AGN feedback Stellar population synthesis (with arbitrary

IMF)

Overview | Models | Science | Collaboration

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SPH vs. SAM Stellar Mass Functions

SPH (GIMIC; Crain et al. 2010)

12.011.010.09.0

SAM (Bower, Benson, Crain 2011)

Two methods produce near identical results... ...when assumptions are matched

Overview | Models | Science | Collaboration

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Decaying Dark MatterOverview | Models | Science | Collaboration

Peter & Benson (2010; PRD; 82, 3521)

X Y

ζ

MY=M

X(1-ε)

ε ≪ 1

Y gets non-relativistic kick vk≈εc

Decay time is τ

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Decaying Dark MatterOverview | Models | Science | Collaboration

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CCAT Mock Surveys

Comoving coordinates (Mpc)

Sky projection (degrees)

Overview | Models | Science | Collaboration

25 m sub-mm telescope Up to 1 square degree field of view 200μm to 3mm wavelength range

Caltech-Cornell Atacama Telescope

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Example SED

StarsCirrusMolecular cloudsTotal

Overview | Models | Science | Collaboration

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Summary

Collaborate.... Developing observing strategies Getting predictions Exploring the effects of different/new physics Improving existing modeling of physics

...or Don't Collaborate! Model is freely available and well documented Use it for what ever you want

Overview | Models | Science | Collaboration GALACTICUS

sites.google.com/site/galacticusmodel