Modeling the Physics of Galaxy Formation
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Modeling the Physics ofGalaxy Formation
Andrew Benson
California Institute of Technology
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Scientific classification Theorist
Scale Galactic – cosmological
Wavelength range Zero – infinity
Favorite color Dark matter
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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