1. THE
GALAXY
Prepared by: Myrell Joyce Esteban

2. Two Models of Galaxy
Formation and Evolution
The Classical or Monolithic Model
•proposes that galaxies form and evolve
as relatively isolated bodies.
•In this scenario galaxies evolve in a
pre-determined fashion dependant on
the initial conditions and with relatively
little impact from the surrounding
environment

3. The Hybrid Hierarchical Model
proposes that galaxies
form and evolve through
successive mergers of
smaller bodies and their
fate is more dependent on
the environment which
they inhabit.

4. Figure 1: The two competing models of galaxy formation and evolution that
could produce the galaxies we observe today. The classical ‘top down’ or
monolithic model is shown on the left. This involves the collapse of a large
cloud over time. The hierarchical or ‘bottom up’ model is shown on the right and
involves successive mergers of small bodies.

5. Figure 2: A simplified schematic of the hybrid
hierarchical model of galaxy formation and evolution .

6. The Evidences
1.Cold Dark Matter (CDM)
It is created in the early stages of the Big
Bang and survives to the present time in
sufficient numbers to contribute
significantly to the present density of the
Universe. The term ‘cold’ signifies that
these particles move at speeds much less
than that of light, usually because they are
heavy.

7. 2. Blue Galaxy
Figure 5: These 18 small blue objects imaged by the HST could be the
precursors to galaxies we see in the universe today.

8. 3. Star Formation Rate (SFR)
The history of recent star formation from the recent compilation of Blain (2000). Data
points are taken from a variety of sources referenced in that article. Thick solid and
dashed lines represent trends expected from simple luminosity evolution and hierarchical
models, respectively. It is clear there is considerable observational scatter at all
redshifts, not just beyond z 1 as often assumed.

9. Cluster of Galaxies
are the largest known gravitationally bound
objects to have arisen thus far in the process of
cosmic structure formation. They form the
densest part of the large scale structure of the
universe. In models for the gravitational
formation of structure with cold dark matter,
the smallest structures collapse first and
eventually build the largest structures, clusters
of galaxies. Clusters are then formed relatively
recently between 10 billion years ago and now.
Groups and clusters may contain from ten to
thousands of galaxies.
.

10. Two classes of Clusters in terms of shape
1. Regular Clusters
are relatively compact, with highest
density near the center. Members are
mostly elliptical galaxies.
2. Irregular Clusters
including our Local Group, have a looser
structure with little central
concentration and less very hot gas.

11. Superclusters
large groups of smaller galaxy groups and
clusters and are among the largest
structures of the cosmos. They are so
large that they are not gravitationally
bound and, consequently, partake in the
Hubble expansion

12. Clusters of Galaxies
Cluster of Galaxy

14. How Did Large-Scale Structure
Evolve In The Universe?
The Hubble Deep Field will be used to perform a
statistical study of the distribution of galaxies on
the sky. This is an essential test of models for the
structure of the universe and galaxy formation
theories. Predicting how clustering should vary
with brightness (or other galaxy properties) is a
key challenge to models of structure formation.
Current observations show that galaxies tend to
cluster around other galaxies. However, the
faintest galaxies are almost randomly distributed
on the sky. The Hubble Deep Field will push such
studies to fainter limits.

15. Active Galaxies
A galaxy emitting unusually high quantities of radiation from
an active galactic nucleus at its center. Some active galaxies
emit more energy in radio wavelengths than they do visible
light
Properties:
(1) High Luminosity,
(2) Nonthermal Spectra that do not look like the sum of many
stellar spectra,
(3) Most of the luminosity is in a region of the spectrum other
than optical (e.g., radio, UV, Infrared),
(4) bright, star-like nucleus,
(5) strong emission lines (most),
(6) rapid variability, and sometimes
(7) radio jets.

16. Starburst Galaxy BL Lac

17. Normal galaxy
one that does not have material for the
supermassive black hole to "feed" on. But
even if these normal galaxies are quite in
regards to core activity, they still emit in
other wavelengths.

18. X-ray Image Mid Infrared Image

19. Differences between
Normal Galaxy and Active Galaxy

20. Quasars
a very energetic and distant active
galactic nucleus. Quasars are the most
luminous objects in the universe.
Quasars were first identified as being
high redshift sources of electromagnetic
energy, including radio waves and visible
light, that were point-like, similar to stars,
rather than extended sources similar
to galaxies.

21. The region of the sky containing one of the high-energy quasars, PKS 0528+134, is shown
at two different times using the EGRET instrument on the Compton Gamma-Ray
Observatory These active galaxies are highly variable, strongly emitting gamma-rays
sometimes, disappearing at other times.

22. THANK YOU!!!
THANK YOU!!!
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BLESS YOU!!!
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