Clustering Discussion Session

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# Clustering Discussion Session - PowerPoint PPT Presentation

Clustering Discussion Session. Understanding LAE - Heidelberg 09/oct/08 Chair: Harold Francke, U. de Chile. Why do we care?. Clustering measurements allows the testing of DM hosting halos (of LAEs) Masses, number densities Can constrain evolution of LAE

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### Clustering Discussion Session

Understanding LAE - Heidelberg 09/oct/08

Chair: Harold Francke, U. de Chile

Why do we care?
• Clustering measurements allows the testing of DM hosting halos (of LAEs)
• Masses, number densities
• Can constrain evolution of LAE
• Evolution of DM halos is known in CDM cosmology.
• Gives clean measurement of the occupation fraction of LAE on their hosting halos
• Using LAEs as tracers of LSS, we can constrain cosmological parameters

Talks by Ouchi san & Gawiser san

Talk by Blanc kun in the morning…

Basics
• Two-point autocorrelation function:

P=n2(1 + (12))d1d2 (angular)

P=2(1 + (r12))dV1dV2 (spatial)

Corresponds to excess probability of finding two points in areas (volumes) d1 and d2 (dV1 and dV2) separated by 12 (r12).

• Correlation lengthr0 , slope : (r) = ( r / r0 )-
What does this look like?
• Real galaxies show a power law correlation function
Halo Mass and clustering

Dark matter halos are biased tracers of the matter field.

Autocorrelation function in a numerical simulation…

From 2D into 3D…

dist

observer

SPATIAL correlation function

ANGULAR correlation function

Beware of narrow redshift distributions! (Simon 2006)

distance distribution

Cosmic variance?
• If in a survey we detect N galaxies with angular corr. (), the variance in this number is:
• LAE surveys are spatially thin
• there are less projection effects
• () is considerable
From statistics to halos
• Bias factor: relates halos to mass
• At large scales, the bias is a constant (linear regime)
• Short scales (~Rvir) non-linear collapse and non-gravitational effects play a role
From statistics to halos
• bias(M) can be calculated from theoretical prediction for halo collapse (Mo&White ‘96 and revisions)
• Number densities can be calculated from the halo mass function (Press&Schechter ‘74 and revisions by Sheth&Tormen, 1999-2002)
From statistics to halos
• Having a simulation at hand (semianalytical or hydro), you can compare (r) directly and measure masses and number densities in the simulation.

(C. Lacey’s & A. Orsi’s talks yesterday)

These models should also reproduce the clustering measurements that exist!!

LAE clustering issues
• What are the masses of the halos containing them?
• How many halos are occupied?
• How does LAE clustering relate to Lya and continuum luminosity?
• How do LAEs at redshift X relate to galaxy type Y at redshift Z?
LAE clustering issues
• How do LAEs at redshift X relate to galaxy type Y at redshift Z?

New samples:

at z~3: McLinden poster

at z~2: talks by Nilsson, Reddy)