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Lick Galaxy Map. CfA Slice with Great Wall. Observing the Clustering of Matter and Galaxies. History: 1920- : galaxies in and around the local group are not distributed randomly 1950-1970: Shane and Wirtanen made maps of the (projected) galaxy distribution

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observing the clustering of matter and galaxies

Lick Galaxy Map

CfA Slice with Great Wall

Observing the Clustering of Matter and Galaxies


1920- : galaxies in and around the local group are not distributed randomly

1950-1970: Shane and Wirtanen

  • made maps of the (projected) galaxy distribution
  • Non-random distribution on small to large scales

1980-1990: Geller, Huchra and many others

  • made maps of the 3D galaxy distribution
  • Depth variable redshift (not quite distance)

2000+: 2DF Redshift Survey / SDSS

  • 100,000 galaxies with spectra

(Literature: e.g. Peacock: Cosmological Physics, p500-509)

Vatican 2003 Lecture 20 HWR

describing the statistics of clustering
Describing the Statistics of Clustering
  • There is no unique way to describe clustering!
    • Need to describe the degree of clustering not the particular configuration.
    • Isotropy: clustering = f(x,y,z)  f(r)
  • Often-used measures are:
  • Angular or real-space correlation function
  • Genus curve
    • Smooth galaxies on different scales
    • Which fraction of the volume is filled by curves of a given over-/under-density
  • Counts-in cells
  • Main practical problems/issues:
    • Complicated search volumes
    • Finite number of tracers
    • Redshift space distortion

Vatican 2003 Lecture 20 HWR

correlation functions
Correlation Functions
  • Excess probability of finding one galaxy (mass element) “near” another galaxy:

- for a random (uniform) distribution: dP = n dV

n: mean number density

- a clustered distribution can be (incompletely) described by:

dP(r) = n [1 + (r)] dV, where dP is the probability of finding a second object near an object at r = 0

(r): two-point (or, auto-) correlation function

Note: (r) = < (x) (x+r) >, where (x) is the fractional over/under-density

- to account for translation and rotation invariance (cosmological principle) often the Fourier transform is used

P(k)   | k|2  =  (r) eikr d3r P(k): power spectrum

- practical estimation:

Vatican 2003 Lecture 20 HWR


If no redshifts (distances) are available, one can define the angular correlation function dP () = n (1 + w() ) d

  • Note:
  • understanding the sampling window function of a survey is crucial
  • usually one is measuring the correlation of tracers

Vatican 2003 Lecture 20 HWR

the clustering of galaxies in the present day universe from the 2dfrs

Red galaxies

Blue galaxies

„Redshift“ Distance

Angle on the sky

The Clustering of Galaxies in the Present Day Universe (from the 2DFRS)
  • Redshift-space correlation

Vatican 2003 Lecture 20 HWR

finger of god and inflow signature

Axis ratio of the correlation in the space-velocity plane as a function of scale

Infall 

 Finger-of-God

Finger-of-God and Inflow Signature
  • pairwise velocity dispersion from “finger-of-god”: 400km/s
  • Cosmic density estimate from inflow: b = W0.6/b = 0.43  0.07

Vatican 2003 Lecture 20 HWR

galaxy clustering vs galaxy properties

From Peacock et al 2002

More luminous/massive galaxies are more strongly clustered

Galaxy Clustering vs. Galaxy Properties
  • Galaxies with little star-formation (~ “early types”) are much more strongly clustered on small scales
  • A.k.a. morphology-density relation
  • Presumably:dense environments lead to rapid/early completion of the main star-formation

Vatican 2003 Lecture 20 HWR

cosmological parameters from the clustering of nearby galaxies

Baryon wiggles? 

Cosmological Parameters from the Clustering of (Nearby) Galaxies

Galaxy correlation now reflects:

  • initial fluctuations
  • growth rate (enter W and L)
  • transfer-function
  • Galaxy bias

Comparison most straightforward in the linear regime >5-10 Mpc

Vatican 2003 Lecture 20 HWR

mass galaxy clustering at high redshift
Mass/Galaxy Clustering at high Redshift
  • Can one observe the growth of mass fluctuation and galaxy clustering directly?
    • Put a “point” between the CMB and the present epoch.
  • Two possible probes at z~3:
    • Galaxies (Ly-break galaxies)
    • The fluctuation inter-galactic medium (IGM): Ly-alpha forest
  • Galaxies:from Adelberger, Steidel and collaborators:
    • Ly-break galaxies at z~3 are nearly as clustered as L* galaxies now
    •  (massive) galaxies were more biased tracers of the mass fluctuations than they are now.

Vatican 2003 Lecture 20 HWR

the ly alpha forest and mass fluctuations
The Ly-alpha Forest and Mass Fluctuations
  • What causes the fluctuation Ly-alpha absorption?
    • Collapsed objects (mini halos)
    • General density (+velocity) fluctuations

Vatican 2003 Lecture 20 HWR

simulating the ly alpha forest cen ostriker miralda 1994 croft katz weinberg hernquist 1996
Simulating the Ly-alpha forest(Cen, Ostriker, Miralda 1994-; Croft, Katz, Weinberg, Hernquist 1996-)
  • Much of the Ly-alpha forest arises from modest density fluctuations and convergent velocity flows!!

Vatican 2003 Lecture 20 HWR

the correlation of igm absorption at different redshifts
The Correlation of IGM Absorptionat different redshifts
  • This probes the mass between galaxies
  • One can follow the evolution of structure with redshift

Vatican 2003 Lecture 20 HWR

combining the cmb with the low z universe



Verde 2003

Combining the CMB with the low-z Universe
  • Until the last few years (BOOMERANG, MAXIMA, WMAP), the CMB fluctuations were measured on larger (co-moving) scales than the fluctuations measured in the low-z universe
  • Only joint extrapolation in redshift and scale possible!

With new generation of z<5 LSS measurements and CMB experiments, a much more direct comparison is possible.

 Impressive confirmation of structure growth prediction!!

Vatican 2003 Lecture 20 HWR

joint constraints from large scale structure and the cmb
Joint Constraintsfrom large scale structure and the CMB
  • Note:
    • this is pre-WMAP, I.e. data from COBE + ground-based and baloon experiments!

(from Peacock et al 2003)

    • h  H0=100

Vatican 2003 Lecture 20 HWR

let s recapitulate

Big Bang


FRW/cosmological parameters


(Non-baryonic) dark matter dominates

(small) initial fluctuations

Growth of density fluctuations




Space is flat, CMB is uniform, fluctuations are scale free

SN Ia, Galaxy Clustering, CMB



CMB vs large-scale structure

IGM fluctuations

Galaxy large scale struture

Let’s Recapitulate

Vatican 2003 Lecture 20 HWR

recapitulation ii

Non-linear growth of densities


(dark matter) halo profiles

Hierarchical build-up of Structures

Successive conversion of gas into stars

Cooling, Feed-back


Remaining hot gas in clusters and IGM


Abundance, stellar mass and clustering of galaxies

dynamics, lensing

Observed merging, fewer massive galaxies at high-z(?)

Recapitulation II

Vatican 2003 Lecture 20 HWR

galaxy properties recapitulation

Global star-formation history and QSO evolution(z>6 to now)

Galaxy luminosity function and colors (as function of z)

Morphologies, Bulge/Disk, etc f(z)

vs. mass

vs. environment

Typical Sizes

Global Scaling Relations

Fundamental plane, Tully-Fisher

MBH – s relation


Hierarchical merging and gas supply

Gas cooling, feed-back, cold gas supply

Gas Disks Merging  Spheroids

Hierarchical picture

Hierarchical picture

Angular momentum (but is it lost?)

Constant star fraction; similar ang.mom.

Good thing to work on…

Galaxy Properties Recapitulation

Vatican 2003 Lecture 20 HWR