The Effects of Baryons on Dark Matter Halos: A Brief Summary - - PowerPoint PPT Presentation

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The Effects of Baryons on Dark Matter Halos: A Brief Summary Andrew R. Zentner University of Pittsburgh Outline 1. Overview of Structure Formation 1.1. Dark Matter Halos and Halo Structure 1.2. Galaxies and Galaxy Formation 2. Baryonic

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The Effects of Baryons on Dark Matter Halos: A Brief Summary

Andrew R. Zentner University of Pittsburgh

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Outline

  • 1. Overview of Structure Formation

1.1. Dark Matter Halos and Halo Structure 1.2. Galaxies and Galaxy Formation

  • 2. Baryonic Influences on Dark Matter Halos

2.1. Halo Contraction 2.2. Halo Shapes 2.3. Halo Substructure (Subhalos)

  • 3. Effect on Dark Energy Measurements
  • 4. Summary & Future
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Why Care?

  • 1. Contraction affects tests of dark matter on a

variety of scales, using a variety of techniques 1.1. Rotation Curve Measurements 1.2. Gravitational Lensing Tests 1.3. Direct DM Search Signal Predictions 1.4. Abundance of Halo Substructure (subhalos) 1.5. Halo Shape Tests for DM Self-Interactions 1.6. DM Annihilation Luminosities & Morphologies

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Halo Structure

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SLIDE 5
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Dark Matter Halos

  • Halos are “building

blocks” of Nonlinear structure

  • Virialized “Halos”

have masses and radii...

Mvir = 4π 3 ∆ρ R3

vir

∆ ∼ 200

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SLIDE 7

Dark Matter Halos

  • Halos have

spherically-averaged density structures...

  • The concentration

parameter “c” specifies how centrally concentrated the dark matter is at fixed

  • verall, Mvir

ρ(r) ∝

  • c

r Rvir −1 1 + c r Rvir −2

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Subhalos

  • “Subhalos” are the

self-bound, smaller clumps the Lie within the “Virialized” regions

  • f larger “Halos”
  • Subhalos are, to

rough approximation, much like smaller, denser halos

Subhalos

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Dark Matter Halos

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Galaxies Form in Halos

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Galaxy Formation & Halo Contraction

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Halo well-mixed, baryonic Gas

L

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Halo

L

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Halo “Spiral” Galaxy

L

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Halo “Spiral” Galaxy Energy “Feedback” by a central quasar?

L

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Adiabatic Contraction

r M(<r) is an adiabatic invariant for circular orbits

Steigman et al. 1978; Zel’Dovich et al. 1980; Blumenthal et al. 1986

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Adiabatic Contraction

Use r × M(<〈r〉) as an invariant to account for noncircular orbits

Gnedin et al. 2005

Fit, 〈r〉= Arvir (r/rvir)w to particle orbits

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Halos with Galaxies

galaxy formation non-radiative Gas dissipationless n-body

Modify Halo structure, account for contraction, compute lensing spectra Halos in baryonic simulations look like NFW halos with modified concentrations

Rudd et al. 2008 Also: Guillet et al. 2009; Casarini et al. 2010

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Halos with Galaxies

  • Modified Halo Concentration Relation

Relative to the Standard N-Body Result

Rudd et al. 2008

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Example Contraction

Duffy et al. 2010 Density “Weak” Feedback “Strong” Feedback See also: Gnedin+04; Gustafsson+06; Pedrosa+09; Tissera+10; Wang+10

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Contraction Model Residuals

Wang et al. 2010 Similar: Gustafsson+06; Pedrosa+09; Tissera+10; Duffy+10

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Is there evidence for contraction?

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Yes?

Dark matter contribution to mass based on velocity dispersions & stellar population modeling Mass implied by weak lensing on large scales & NFW assumption for halo

Schulz et al. 2010

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No?

Dutton et al. 2010 Also: Gnedin et al. 2006; Sand et al. 2008; Simon et al. 2008; Trachternach et al. 2008; de Blok et al. 2010... ratio of measured star/gas speeds to halo virial speed measured speeds within galaxies Points: Simulations Galaxy Data Compilation

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Can the simple model be “Corrected”?

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Adiabatic Contraction

Use r × M(<〈r〉) as an invariant to account for noncircular orbits

Gustafsson+06; Wang+10; Duffy+10

〈r〉= Arvir (r/rvir)w fit A & w to get better contraction model!

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Orbit Correction?

Duffy et al. 2010 Similar: Gustafsson+06; Wang+10 “Weak” Feedback “Strong” Feedback

  • 1. “Best” model does not reflect particle orbits!
  • 2. “Best” model depends upon baryonic feedback

and assembly history: complicated!

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Halo Dependence?

Wang et al. 2010

  • 1. Residuals depend upon dark matter halo

properties

High Concentration Low Concentration

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Failures are not surprising

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Halo Shapes

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Halo

L

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Halo well-mixed, baryonic Gas

L

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Halo Galaxy

L

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Halo Galaxy

L

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a b q=b/a s=c/a

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a b q=b/a s=c/a

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Shapes in DM-Only Halos

Zentner et al. 2005 See also: Allgood et al. 2007

  • Halos in DM-Only simulations

typically are not round, q≈0.65 & s≈0.6

  • However, many inferences

drawn from local group data suggest a nearly spherical MW halo (Olling+00; Ibata+01; Majewski+03; Helmi+04; Johnston+07; Majewski+08; Smith+10)

  • Distant galaxy halos as well...

(Dubinski+91; Olling+00; Buote +02; Hoekstra+04; Mandelbaum +08; Buote+09)

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With Baryons

  • 1. Halos become significantly more spherical

when baryons cool and form galaxies

No Baryon cooling With Baryon cooling

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With Baryons

r/Rvir 0.1 1.0

Kazantzidis et al. 2005

  • Baryonic cooling in

simulations gives dramatic changes in halo shape (but not velocity anisotropy; Tissera+2010)

  • Changes as large as

∆(c/a)≈0.2 are typical

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Testing This

Lau et al. 2010

  • Mock X-ray maps of simulated clusters

No Baryon cooling With Baryon cooling

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Testing This

Lau et al. 2010

  • Mock X-ray maps of simulated clusters compared to data...
  • Elliptical shapes of

cluster suggest minimal shape transformation (and minimal cooling?)

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Locally

Pato et al. 2010

  • Shape of halo may have interesting consequences for direct

and indirect search results locally...

[rad]

  • 1

2 3 4 5 6

]

3

/kpc [M

  • 5

10 15 20 25

6

10

  • SR6-n01e1ML

stellar disk [rad]

  • 1

2 3 4 5 6

]

3

/kpc [M

  • 5

10 15 20 25

6

10

  • SR6-n01e1ML
  • rthogonal to stellar disk (1)
  • Stellar disk enhances DM density in the plane (compared to

measures that average spherically to derive DM density)

  • Deviations from axial symmetry lead to time-dependent

density along the Sun’s orbit.

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Halo Substructure with Baryons

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Galaxy

Disk “Heating”

Subhalo Orbit

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Galaxy

Disk “Heating”

Subhalo Orbit Accelerations of Particles on Halo Outskirts

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Disk Consequences

Kazantzidis et al. 2010

  • The disk is heated and disk “features” are generated...
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Subhalo Consequences

D’Onghia et al. 2010

  • The disk “heats” substructure and serves to destroy them

more efficiently than N-body only simulations

Also: Kazantzidis et al. 2009

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Dark Energy?

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Halos with Galaxies

  • Modified Halo Concentration Relation

Relative to the Standard N-Body Result

Rudd et al. 2008

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Parameter Biases

AZ, Rudd, & Hu 2008

Parameter Bias Relative to Statistical Uncertainty Maximum Multipole Under Consideration

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“Conclusions”

  • 1. Some Halo Contraction Likely Happens, but it

is hard to assess the degree and it depends upon messy details of galaxy formation

  • 2. Baryonic Contraction likely makes halos

rounder (altering, in principle, constraints on SIDM), but the degree is again hard to assess

  • 3. The presence of galaxies should reduce the

prevalence of substructure, but the degree is hard to assess

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The Correlation Function

  • Excess probability of finding a galaxy a

distance r, from another:

  • If the local galaxy density is ng = ng [1+δ(x)],

then:

  • and:

dP = ¯ ngdV1 × ¯ ng[1 + ξ(r)]dV2

  • dP= ¯

n2

g [1 + δ(

x1)][1 + δ( x1 + r)] dV1dV2 = ¯ n2

g[1 + δ(

x1)δ( x1 + r)]dV1dV2

ξ(r) = δ( x1)δ( x1 + r)

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SLIDE 55

Correlation Function

Totsuji & Kihara 1969

angular separation correlation function

power laws, ξ∝(r/r0)-s

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The Halo Model

Halo, M1 satellite galaxies

r

Halo, M2

r

  • Compute correlation statistics using halos as the

fundamental unit of structure: ξ(r)=ξ1H(r)+ξ2H(r)

satellite galaxies central galaxy central galaxy

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Analytic Method

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Modeling Framework

time

Gnedin & Ostriker 1999; Gnedin, Ostriker, & Hernquist 2000; Taffoni et al. 2002; Taylor & Babul 2002; Zentner & Bullock 2003; Zentner et al. 2005a,2005b