Transcript Observing the Clustering of Matter and Galaxies

History:
1920-
Observing the Clustering of
Matter and Galaxies
Lick Galaxy Map
: galaxies in and around the local group are
not distributed randomly
1950-1970: Shane and Wirtanen
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made maps of the (projected) galaxy distribution
Non-random distribution on small to large scales
1980-1990: Geller, Huchra and many others
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made maps of the 3D galaxy distribution
Depth variable redshift (not quite distance)
CfA Slice with Great Wall
2000+: 2DF Redshift Survey / SDSS
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100,000 galaxies with spectra
(Literature: e.g. Peacock: Cosmological Physics, p500-509)
Vatican 2003 Lecture 20 HWR
State-of-the-Art Example: 2DFRS
(from Peacock et al 2002)
Star-Forming
Galaxies
Red Galaxies
Vatican 2003 Lecture 20 HWR
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
• 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:  (r ) 
DD(r )  2 DR(r )  RR(r )
RR 2 (r )
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)
• Redshift-space correlation
Red galaxies
Blue galaxies
Angle on the sky
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
– pairwise velocity dispersion from “finger-of-god”: 400km/s
– Cosmic density estimate from inflow: b = 0.6/b = 0.43  0.07
Vatican 2003 Lecture 20 HWR
Galaxy Clustering vs. Galaxy Properties
•
•
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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
Vatican 2003 Lecture 20 HWR
Cosmological Parameters from the
Clustering of (Nearby) Galaxies
Galaxy correlation now reflects:
–
–
–
–
initial fluctuations
growth rate (enter  and L)
transfer-function
Galaxy bias
Baryon wiggles? 
Comparison most straightforward
in the linear regime >5-10 Mpc
Vatican 2003 Lecture 20 HWR
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
• What causes the fluctuation Ly-alpha absorption?
– Collapsed objects (mini halos)
– General density (+velocity) fluctuations
Vatican 2003 Lecture 20 HWR
Vatican 2003 Lecture 20 HWR
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
Comparing Data and Simulations
From Croft et al 1998
Vatican 2003 Lecture 20 HWR
The Correlation of IGM Absorption
at 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
• 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!
z=1100
With new generation of z<5
LSS measurements and CMB
experiments, a much more
direct comparison is possible.
z=0-3
Verde 2003
 Impressive
confirmation of structure
growth prediction!!
Vatican 2003 Lecture 20 HWR
Joint Constraints
from 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
Vatican 2003 Lecture 20 HWR
Let’s Recapitulate
Theory
Observations
Big Bang
Expansion,CMB,BBN
Inflation
Space is flat, CMB is uniform,
fluctuations are scale free
FRW/cosmological parameters
M=0.27,L=0.7,H0=70
SN Ia, Galaxy Clustering, CMB
(Non-baryonic) dark matter dominates
Dynamics,lensing,BBN,CMB
(small) initial fluctuations
CMB
Growth of density fluctuations
CMB vs large-scale structure
IGM fluctuations
Galaxy large scale struture
Linear
Vatican 2003 Lecture 20 HWR
Recapitulation II
Theory
Observations
Non-linear growth of densities
N-body,Press-Schechter
(dark matter) halo profiles
Hierarchical build-up of Structures
Abundance, stellar mass and
clustering of galaxies
dynamics, lensing
Observed merging, fewer massive
galaxies at high-z(?)
Successive conversion of gas into
stars
Cooling, Feed-back
Enrichment
Remaining hot gas in clusters and IGM
Vatican 2003 Lecture 20 HWR
Galaxy Properties
Observations
Recapitulation
Theory
Global star-formation history and
QSO evolution (z>6 to now)
Hierarchical merging and gas supply
Galaxy luminosity function and colors
Gas cooling, feed-back, cold gas
supply
(as function of z)
Morphologies, Bulge/Disk, etc f(z)
vs. mass
vs. environment
Typical Sizes
Gas Disks
Merging  Spheroids
Hierarchical picture
Hierarchical picture
Angular momentum
(but is it lost?)
Global Scaling Relations
Fundamental plane, Tully-Fisher
MBH – s relation
Constant star fraction; similar ang.mom.
Good thing to work on…
Vatican 2003 Lecture 20 HWR