Vatican 2003 Lecture 20 HWR Observing the Clustering of Matter and Galaxies History: 1920- :...
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Transcript of Vatican 2003 Lecture 20 HWR Observing the Clustering of Matter and Galaxies History: 1920- :...
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
Vatican 2003 Lecture 20 HWR
Star-Forming Galaxies
State-of-the-Art Example: 2DFRS(from Peacock et al 2002)
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 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
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
Angle on the sky
Red galaxies
Blue galaxies
„Redsh
ift“
Dis
tance
Vatican 2003 Lecture 20 HWR
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
Vatican 2003 Lecture 20 HWR
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
Vatican 2003 Lecture 20 HWR
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?
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 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
• 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
Vatican 2003 Lecture 20 HWR
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
Vatican 2003 Lecture 20 HWR
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
Vatican 2003 Lecture 20 HWR
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(?)
Vatican 2003 Lecture 20 HWR
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…