Download
1 / 13
130 likes | 224 Views
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.
E N D
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?
