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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 bispectrum Dolney, Jain, and Takada [DJT] astro-ph/0401089 published in MNRAS discussion lead by Stephen Bailey. Halo Model.
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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
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
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 • [?]
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
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]
Bigger Smaller Figure 1 – How do sub-halos affect power? sub-halos increase small 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?
Figure 2 – What contributes what? smooth:smooth within clump smooth:clump clump:clump halo:halo Interesting, but no surprises. Details reflect the specifics of their model
Figure 3 – What size sub-halos contribute? Smaller stuff contributes at smaller scales Is this interesting, or just a reflection of their model inputs?
Figure 4 – comparison with other models Vary halo density profile [?] No substructure varying the halo density profile might be part of the picture
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…
Figure 10 – can we measure substructure? Just weak lensing With CMB Input
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?
