1 : Preliminaries   6 :   Dynamics I 11 : Star Formation  16 : Cosmology
2 : Morphology   7 :   Ellipticals 12 : Interactions 17 : Structure Growth 
3 : Surveys 8 :   Dynamics II 13 : Groups & Clusters  18 : Galaxy Formation 
4 : Lum. Functions  9 :   Gas & Dust   14 : Nuclei & BHs 19 : Reionization & IGM  
5 : Spirals 10 : Populations    15 : AGNs & Quasars 20 : Dark Matter





(1) Introduction

Lets start by identifying some of the salient features of galaxy clusters.


(2) Cluster Surveys and Catalogs

(a) Optical Identification

(b) X-ray Identification

(c) Other Methods of Identification


(3) Cluster Classification


(4) Important Timescales

(a) Crossing Time

(b) Violent Relaxation Time

(c) 2-Body Relaxation and Dynamical Friction Times


(5) Cluster Shapes & Kinematics

(a) "Smoothed" Properties

(b) Substructures


(6) Two Nearby Examples : Virgo & Coma


(7) The Morphology-Density Relation

It is well known that the Spiral/Elliptical ratio is often lower in clusters than the field.
We discussed this in terms of Luminosity Functions in Topic 4.6
It seems the morphology of a galaxy depends (statistically) on its environment
This "Morphology-Density Relation" is important since it clearly plays a role in galaxy evolution :

Lets look more closely at this topic.

(a) Early Work at Low Redshift

(b) Possibly Relevant Physical Processes

Overall, the interpretation of the morphology-density relation is still unclear.
Possibilities include :

(c) HI Deficiency - Stripping of Spiral HI Gas

One of the (several) possible environmental effects on galaxies in clusters is the stripping of ISM due to ram pressure as the galaxy moves through the ICM. Observational work in the 80s focussed on HI and CO :

(d) Recent Work at High Redshift

Only with HST has it been possible to study morphology at high-z (z ~ 0.5; lookback times ~6-8 Gyr).
This gives insight into whether the morphology-density relation stems from galaxy formation or galaxy evolution.

HST studies find :
We conclude from this :

(e) Caveat

This is an active area of research, with many details and uncertainties.
The outline I have given here is cleaner than the true situation at this time.


(8) Luminosity Functions


(9) cD Galaxies

cD galaxies are anomalies in the galaxy population :


(10) The Hot Inter-Cluster Medium (ICM)

Clusters are the most luminous extended X-ray sources in the Universe : 1043-46 erg/s
  emission from hot hydrostatic gaseous "atmosphere"   :   (107-8K)

(a) Simple Physics

(b) Hydrostatic Atmosphere & "Beta" Models

(c) X-ray Correlations

(d) Abundances (and Temperatures)

(e) Cooling Flows

(f) Radio Sources & the ICM

Radio halos & the link to ICM shocks
Not yet written up

(g) ICM Substructures and Cluster Mergers

Not yet written up


(11) Cluster Masses

There are a number of methods for measuring the gravitational field in clusters
To some extent, this topic overlaps with Topic 17 on Dark Matter and Gravitational Lensing
So we will be quite brief here.