Clustering of Galaxies in an Expanding Universe IAS School January 26, 2012 Nanyang Technological University Singapore

Size: px

Start display at page:

Download "Clustering of Galaxies in an Expanding Universe IAS School January 26, 2012 Nanyang Technological University Singapore"

Clement Young
5 years ago
Views:

1 Clustering of Galaxies in an Expanding Universe IAS School January 26, 2012 Nanyang Technological University Singapore Naseer Iqbal University of Kashmir Srinagar, India IUCAA, Pune India

2 Astronomy and Astrophysics ASTRONOMY Oldest observational sciences Study of physical nature and composition of universe and everything it contains We study shape, size, brightness, movements as well as interactions between various objects ASTROPHYSICS Deals with physical laws that govern the structure and behavior of the astronomical objects Emphasizes on the physical and chemical processes in astronomical objects such as birth and evolution of the universe as well as for other objects

3 Out Line: 1. Clusters of Galaxies 2. Gravitational Interaction between them 3. LSS of Universe 4. Theoretical Approach 5. St. mechanics / Thermodynamics 6. Comparison between theory observations 7. Correlation Functions (Theoretical overview) 8. Temperature of a cluster / Peculiar velocity

4 Matter in the Universe The world around us is made of ordinary matter! Ordinary matter is made of atoms and molecules (19 th century chemistry) Atoms are made of atomic nuclei and electrons (beginning of 20 th century) Atomic nuclei are made of protons and neutrons (1930 s) Protons and neutrons are made of quarks and gluons (1970 s) Atomic spectroscopy indicates the sun, the milky way, and all stars in the sky are made of ordinary matter!

5 Galaxy Stars + ISM + Supernova remnants + Cosmic rays + Magnetic field. A galaxy is a gigantic mixture of all the above material that combine to form small separate islands in the universe. Miliky-way is our own galaxy. Observational part of universe

6 Galaxies (Various types) Spiral Elliptical Irregular

7 Galaxies (Types) Spiral galaxies Elliptical galaxies Irregular galaxies Infrared Image of the core of Milky way Galaxy

8 E indicates elliptical type, S indicates spiral type SB represent barred spiral type

9 Galaxy Clusters Galaxies are preferentially found in groups or larger agglomerations called clusters. Clusters are in the form of Regular clusters, Irregular clusters. Regular clusters have a concentrated central core and a well defined spherical structure. Irregular clusters have no well-defined centre

10 Galaxy Galaxy Cluster Members of a group

11 Galaxy clusters (Various types) A cluster contain 50, - 1, 000 galaxies, hot X- ray emitting gas and large amounts of dark matter. They have total masses of to solar masses. Typically have a diameter from 2 to 10 Mpc. Notable galaxy clusters include Virgo cluster, Hercules cluster and the Coma cluster.

12 Observational Methods Optical and Infrared;-Optical and Infrared telescopes are used X-rays;-X ray telescopes are used by studying X-ray imaging and spectroscopy Radio;- Groups of radio sources have been found in Cluster formation Gravitational lensing;- Galaxy clusters contain enough matter to distort the observed orientations of galaxies behind them

13 Large scale structure(lss) Superclusters usually consist of about dozen clusters which have a mass of about solar masses. Virgo is our local supercluster with a size of 15 Mpc. Superclustering system forms network through space, on which about 90% of galaxies are located Voids, sheets and filaments;

14 More and more theoretical models Construction of theoretical model is always based on some postulates Galaxies are the building blocks of the universe Galaxy-Galaxy is bound together by a mutual physical force called Gravity On large scale galaxies are assumed to be point mass particles

15 Why to study galaxy clusters? 1. Important role in the evolution. 2. Study of LSS on the basis of galaxy clusters is one of the important challenge in modern cosmology. 3. Nowadays we are able to study the cosmological phase transitions on the basis of clustering phenomena. 4. Study of peculiar velocities.

16 St. Mechanics of cosmological many body problem 1. Why we use St. Mechanics? Ensemble theories. 2. Can we use thermodynamics as well?

17 How galaxies behave in LSS Galaxies Cluster under the influence of their mutual gravitational force. Observations have shown that the galaxies are not randomly spaced. Galaxies are connected in web of sheet like structures to give large scale structure. To understand the large scale structure and distribution of galaxies many methods have been given which include distribution functions, low-order correlation functions, fractals etc.

18 Applicability of thermodynamics Thermodynamics is applied to equilibrium systems and self-gravitating systems are never in equilibrium. The local dynamical time scale in an over dense region is faster than global gravitational time scale: > >

19 Then what? This difference makes it possible for gravitational clustering to evolve through a sequence of quasi-equilibrium states. In other words, local equilibrium arise faster than cosmic expansion can disrupt them As the gravitational clustering dominates, the macroscopic evolution of a Cluster occurs on a timescale longer compared to Hubble expansion time scale.

20 Saslaw and Hamilton (1984) The average thermodynamic properties change slowly on these scales and system can be adequately described by macroscopic thermodynamical variables

21 Equations of state: Virial theorem:in the stationary gravitational system, the potential energy is twice the kinetic energy!

22 b can also be defined as: Measures of b (0 1)

23 Ahmad (1998): combination of Ist and 2 nd law of thermodynamics

24 Grand Canonical ensemble theory

38 Some thing Important here?

39 Main difficulty and its immediate remedy?

40 Achievements' with this theory?

41 For details pl see Ap. J 2002, Vol. 571, 576(Ahmad, F, Saslaw, w.c and Bhat Naseer Iqbal)

42 Correlation functions in galaxy clusters Correlation functions The two-point correlation function is defined as the excess probability, compared with that expected for a random distribution, of finding a pair of galaxies at a separation r12

43 BBGKY Hierarchy equations complicated for higher order correlations 2-point correlation the simple tool We proceed with same thermodynamics make use of equations of state

45 Extended mass structures:

48 After we use the solution of ξ in b equations, all the previous results of Saslaw and Hamilton (1984) get confirmed, this confirms the validity of our thermodynamical model Our results show the validity of power law Our study provides an alternative way of measuring correlation functions in galaxy clusters For details, pl see, JAA (2006), VOL. 27, 373 Iqbal N, Ahmad F and Khan M S.

49 Our Present Interest? Study of Individual temperature Profile of galaxy clusters Study of Peculiar velocity of galaxy clusters Study of Phase transitions in galaxy clusters on the basis of peculiar velocity Study of phase transitions on the basis of entropy change in galaxy clusters

50 Encouraging results but need lot of study Comparison between Theory / Observations

51 THANKS FOR YOUR PATIENT HEARING

Part two of a year-long introduction to astrophysics:

ASTR 3830 Astrophysics 2 - Galactic and Extragalactic Phil Armitage office: JILA tower A909 email: pja@jilau1.colorado.edu Spitzer Space telescope image of M81 Part two of a year-long introduction to astrophysics: