Clustering and environments of dark matter halos

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Clustering and environments of dark matter halos

• Yipeng Jing
• Shanghai Astronomical Observatory

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Evolution of large scale structures
The importance of studying dark matter halos
1)in CDM models, all dark matter is in halos of
different mass 2) shaping up luminous objects,
such galaxies and clusters 3) dark matter halos
could be directly detected by gravitational
lensing
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Three important aspects of dark matter halos

• Mean number mass function f(m)dm
• Spatial distribution correlation functions bias
  factors, etc.
• Internal properties of dark matter density
  profile, spin,etc

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Excursion Set Theory for identifying dark
matter halos from Gaussian Initial density field
Bond et al. 1991, ApJ
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Predictions of the Excursion Set Theory
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Test of the Excursion theory mass function
Lee Shandarin 1998, ApJ
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Jing et al. 2006 in preparation ??????????????????
?(Based on the background-split assumption and
the bias model)
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• Test of the bias (Jing 1998, ApJL)

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Empirical Modification for MF and bias (based on
peak background split)

• Sheth Tormen (1999) MNRAS

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(No Transcript)
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Environmental effect

• Lemson Kauffmann (1999) spin, concentration,
  no dependence
• Percival et al. (2003) clustering vs age, no
  dependence
• Gao et al. (2005), MNRAS, found age dependence
• Main Reason Gao et al examine MltltM halos

Formation time at the time when the most massive
pregenitor has accumulated a half mass
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Concentration vs formation time
Jing (2000) ApJ see also Bullock et al. (2001),
Wechsler et al. (2002), Zhao et al (2003a,b)
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Clustering vs concentration
Wechsler et al. 2006/astroph0512416

• Small halos agree with Gao et al.
• Big halos reversed
• Small and big halos Not at the same epoch

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Reversal not found for formation time ??
Wetzel, et al. 2006 Astroph/0606699
For massive halos confirmed the dependence on c
but not found for the formation time
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An accurate determination at high halo mass
Jing, Suto, Mo 2006, to be submitted
A set of N-body simulations of 1 billion
particles Using cross-power spectrum
method Superior over the correlation function
method
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Cosmological N-body simulations at SHAO with
10243 particles
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The dependence on the formation time is detected
at gt10sigma for large halos, though small !
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Why old, low mass halos are more strongly
clustered?
Wang, Mo, Jing (2006), astroph/0608690 (MN in
press)
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Association with high initial collapse region
(SC) leads to high clustering of old population
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Tidal stripping/pancake heating suppress
formation of low mass halos in high density
regions (cf. Mo et al 2005 MN, Lee 2006
astroph/0605697)
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Observational Evidence?
Using 2dF catalogs of galaxies and groups, and
the cross correlation Using ? (current SFR)of the
central as the proxy for z_f Yang et al. (2005)
ApJL
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Consequences for Halo Occupation Distribution
Studies (Zhu et al. 2006, ApJL)
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Limitation for precision measurement with HOD
Croton et al. 2006 Astroph/0605636
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Summary

• The dependences of halo clustering on both
  formation time and the concentration are well
  established
• The dependence at low mass is largely due to the
  failure of the spherical model providing clues
  to improve EST
• The dependences at high mass still are
  challenging to Excursion Set Theory
• Preliminary observational evidence, but not fully
  consistent
• Important for precision cosmology studies with
  HOD color dependence