Clumps within Lumps
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Transcript of Clumps within Lumps
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Clumps within Lumps
or, why adding small scale substructure increases the small scale power spectrum…
Effects of halo substructure on the power spectrum and bispectrumDolney, Jain, and Takada [DJT] astro-ph/0401089published in MNRAS
discussion lead by Stephen Bailey
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Halo Model
Instead of full N-body simulations, track clumps of dark matter (haloes)
Does a pretty good job of matching N-body simulationswith a lot less work
See Corray and Sheth (2002) Phys. Rep. 372, 1 for a review
From Cooray and Sheth, 2002
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Basic Ingredients
Mass functions How many halos there are of a given mass
Halo density profile How the matter is distributed within a halo Spherically symmetric Smoothly decreasing with radius
Bias prescription [?]
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The Problem
N-Body simulations have halo substructure 10%-ish of halo matter is in a sub-halo clump This shouldn’t be too surprising
the halo model is a pretty severe limit which works surprisingly well adding substructure is a first order correction back toward the truth
Several recent papers discuss halo substructure DJT try to quantify the size of the effect and relate it to future
measurements
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What DJM do
Standard halo model, plus Sub-halos within each halo, with their own density distributions,
mass functions, etc. Sub-halo density follows the parent halo density They ask: How does this affect the power spectrum?
power spectrum [2 point correlation] bispectrum [3 point correlation] reduced bispectrum [3 point normalized by 2 point squared]
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Figure 1 – How do sub-halos affect power?
Bigger Smaller
sub-halos increasesmall scale power(no surprise)
Questions:- Why Smith et al. (2003)?- Normalization between 0%, 10%, 20%?- What size scales are galaxies, clusters, superclusters, etc.?- What size does weak lensing probe?
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Figure 2 – What contributes what?
smooth:smooth
within clump
smooth:clump
clump:clump
halo:halo
Interesting, but no surprises.Details reflect the specificsof their model
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Figure 3 – What size sub-halos contribute?
Is this interesting, or just areflection of their model inputs?
Smaller stuff contributes at smaller scales
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Figure 4 – comparison with other models
No substructure
Vary halo density profile [?]
varying the halo density profile might be part of the picture
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Figure 6 – other cosmological effects
Other cosmological parameters mimic substructure
But they each affect different measures in different ways spectrum (2 point) bispectrum (3 point) reduced bispectrum
(3 point / 2 point) So there is hope for
disentangling this
Side notes:• yay! for model error bars!• they might spoil the day…
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Figure 10 – can we measure substructure?
With CMB Input
Just weak lensing
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Questions and Comments
I don’t see anything deep, subtle, or surprising in their results But it is important to make quantitative comparisons between
models and relate simulations to observations
Their claim: with SNAP-like weak lensing and Planck-like CMB, we should be able to measure halo substructure It would be nice to be able to test models against data rather
than against each other…
DJM aren’t the first authors to use sub-halos in their halo models What have they done which is new? and/or Why didn’t the other authors do it first?
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Movie(from Ma & Bertschinger)