Galaxy Clusters & Large Scale Structure

Ay 16, April 3, 2008

Coma Cluster

=A1656

Galaxies Are Not Randomly Distributed in Space

Fundamental discovery (and debate) in the 20th century is that Galaxies cluster.

On small scales: Binaries ~100 kpc intermediate scales: Groups ~1 Mpc larger scales: Clusters few Mpc even larger scales: Superclusters 10’s Mpc largest seen: Voids + Cosmic Web ~50 Mpc

M51 = Whirlpool = NGC 5194+95

NOAO

Seyfert’s Sextet

Stefan’s Quintet

Abell 1689

Coma Cluster

Coma in X-rays

Mass Estimators:

• MV =

• MP = Σ Ri (Vi-VG)2

with fPM =10.2 and γ = 1.5 (Heisler, Tremaine & Bahcall 1985, ApJ 298, 8)

3 π ΣσP2 RP

2 G

fPM

π G (N – γ)

Hydrostatic Equilibrium

Abell 2142 in X-rays CXO

Gravitational Lensing

Cluster Mass Estimates

Now three techniques agree fairly well for the same clusters -- Galaxy Dynamics, Gas Hydrostatic Equilibrium + Gravitational Lensing masses give a mean M/L of around 300 in blue light (solar units) and 100 in infrared light. This is important for cosmology as it implies (1) that there’s lots of Dark Matter on large scales, and (2) that matter is ~ 0.25.

PerseusCluster

Shocks in the hotGas

(Fabian+)

Abell 2597

shocks and bubbles

Large Scale Structure

The study of the galaxy distribution on large scales started out with maps.

Election ’06 Congressional Districts

Its all in the display:

Election ’04

By County R/B

By County color range

By state scaled by population

Messier’s map:What do you see?

W. Herschel

New General Catalogue + Index Catalogues

Fritz Zwicky

et al.

CGCG

Zwicky’s Catalog

Early “Modern” Views• Hubble: The Large Scale is “Sensibly

Uniform,” one cluster per 50 square degrees. “General Field of galaxies, isolated groups and clusters.

versus

• Zwicky “Clusters are Common”

“cluster cells separated by saddles or minima ... and … not … flatlands”

Statistics of Clustering

Many different “statistical” measures.

Peebles and Totsuji & Kihara introduced the correlation function -- a measure of the excess probability of finding a galaxy near another galaxy --- in the early 1970’s.

Correlation Functions

2D Angular Correlation Function

dP = N [1 + w()] d

where N = surface density of galaxies = angular separation and = solid angle (area of sky)

3D Spatial Correlation Function

dP = n [ 1 + (r) ] dV

where n is now the volume density

dV is the volume element

and r is some measure of separation

e.g. s = [d2 + ((v1 - v2)/H)2 ]1/2

Hubble’s Discovery of Expansion

Redshift Surveys

3747 +/- 20 CfA Survey

3D Maps of the Local Universe

Not much progress until the mid 1970’s!

Catalogs existed from Photographic Surveys- 2D only (Zwicky++; Vorontosov-Velyaminov++)

In 1972 the largest “complete” galaxy redshift sample had only ~250 galaxies

Key was innovations in detector technology:

computers + digital detectors

sensitive radio receivers

Larson wasn’t quite right…

The

Little Telescope

that could.

Tillinghast

1.5-m

The Z Machine

Davis, Tonry, Latham & Huchra

Based on a concept by

Shectman & Gunn

Spectral features in galaxies

CfA2 Slice

1985 CfA 2 deLapparent, Geller & Huchra

CfA2 1995

6dF Fiber Positioner, SRC Schmidt, Coonabarabran

KS < 11.25

We are here

Great Wall

Pisces-Perseus

LSC

M. Westover

• Magenta V < 1000 km/s • Blue 1000 < V < 2000 km/s• Green 2000 < V < 3000 km/s

Red 3000 < v < 4000

Blue 4000< v < 5000

Green 5000 < v < 6000

Red 3000 < v < 4000

Red 6000 < v < 7000

Blue 7000 < v < 8000

Green 8000 < v < 9000

Red 9000 < v < 11000

Blue 11000 < v < 13000

Green 13000 < v < 15000

SCDM LCDM

Virgo Consortium: testing cosmological models with LSS. Obs vs Simulations

Red = DM from

Grav lensing

Blue = Hot

x-ray gas

Next Steps:o Distances via TF, d_n-sigma, SN, etc. 4000 galaxies inside 15000 km/s with HI and 2MASS photometry (e.g. see the Cornell group’s work) o Redshifts to K=12.25, ~100,000 galaxies all sky (6dF in the south, ??? in the north)

o Hollywood (movies!)

Remember, This Is A Sphere!

Going Deeper: Wide Field Telescopes

The MMT

Hectospec Positioner on MMT

Dan Fabricant et al.

Hectospec Positioner on MMT

300 Fibers

covering a

1 degree field

of view

D. Fabricant

Large Synoptic Survey Telescope

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