Vatican 2003 Lecture 20 HWR Observing the Clustering of Matter and Galaxies History: 1920- : galaxies in and around the local group are not distributed

Vatican 2003 Lecture 20 HWR

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– 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)

Lick Galaxy Map

CfA Slice with Great Wall


Star-Forming Galaxies

State-of-the-Art Example: 2DFRS(from Peacock et al 2002)

Red Galaxies


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


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 functionNote: (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: 2

( ) 2 ( ) ( )( )

( )

DD r DR r RR rr

RR r


• 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


The Clustering of Galaxies in the Present Day Universe (from the

2DFRS)• Redshift-space correlation

Angle on the sky

Red galaxies

Blue galaxies

„Redsh

ift“

Dis

tance


Finger-of-God and Inflow Signature

– pairwise velocity dispersion from “finger-of-god”: 400km/s– Cosmic density estimate from inflow: = 0.6/b = 0.43

0.07

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

Finger-of-God

Infall


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

From Peacock et al 2002

More luminous/massive galaxies are more strongly clustered


Cosmological Parameters from the Clustering of (Nearby) Galaxies

Galaxy correlation now reflects:– initial fluctuations– growth rate (enter and ) – transfer-function– Galaxy bias

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

Baryon wiggles?


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.


The Ly-alpha Forest and Mass Fluctuations

• What causes the fluctuation Ly-alpha absorption?– Collapsed objects (mini halos)– General density (+velocity) fluctuations



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!!


Comparing Data and Simulations

From Croft et al 1998


The Correlation of IGM Absorptionat different redshifts

• This probes the mass between galaxies• One can follow the evolution of structure with redshift


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!!

Verde 2003

z=1100

z=0-3


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



Let’s Recapitulate

TheoryBig Bang

Inflation

FRW/cosmological parametersM=0.27,=0.7,H0=70

(Non-baryonic) dark matter dominates

(small) initial fluctuations

Growth of density fluctuationsLinear

ObservationsExpansion,CMB,BBN

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

SN Ia, Galaxy Clustering, CMB

Dynamics,lensing,BBN,CMB

CMB

CMB vs large-scale structureIGM fluctuations

Galaxy large scale struture


Recapitulation II

Theory

Non-linear growth of densitiesN-body,Press-Schechter

(dark matter) halo profiles

Hierarchical build-up of Structures

Successive conversion of gas

into starsCooling, Feed-back

EnrichmentRemaining hot gas in clusters and

IGM

Observations

Abundance, stellar mass and clustering of galaxiesdynamics, lensing

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


Galaxy Properties Recapitulation

ObservationsGlobal 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 RelationsFundamental plane, Tully-Fisher

MBH – relation

TheoryHierarchical merging and gas

supply

Gas cooling, feed-back, cold gas supply

Gas Disks Merging Spheroids

Hierarchical pictureHierarchical picture

Angular momentum (but is it lost?)

Constant star fraction; similar ang.mom.Good thing to work on…

Documents

Vatican 2003 Lecture 20 HWR Observing the Clustering of Matter and Galaxies History: 1920- : galaxies in and around the local group are not distributed