El universo:

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El universo
Edad 13.7 millardos de años (1 de
error) Expansión 71 km/sec/Mpc actualmente (5
de error) 73 Energía oscura 23 materia
oscura fría 4 átomos de materia
ordinaria Ocurrió una etapa de expansión rápida
(inflación) Se expandirá para siempre.
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The Galaxies
We assume the stars are grouped together into
galaxies and that these form the basic building
blocks of the visible matter in the Universe.

• The image shows the Hubble Deep Field the Hubble
  Space Telescope was pointed at the same region of
  the sky (in the constellation Ursa Major) for 10
  days and images were combined to give the most
  distant optical view of the Universe. Almost
  every object is a galaxy and objects down to
  visual magnitude 30 can be seen.

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Classification of Galaxies

• Using a system proposed by Edwin Hubble (1926
  1936) astronomers classify galaxies into three
  major types
• Spiral (75)
• Elliptical (20)
• Irregular (5)
• The sizes of all three types span a wide range
  from
• dwarf galaxies
• which contain 100 million (108) stars
• to
• giant galaxies
• which contain 1 trillion (1012) stars

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The Hubble Classification
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Spiral Galaxies

• have a disk component and bulge halo
  (spheroidal component)
• disk contains an ISM of gas dust
• relative sizes of bulge/disk amount of ISM vary
  among galaxies
• contain both blue red stars

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Spiral Galaxies
Properties Mass 109 - 1012 M Diameter 5 -
50 kpc Luminosity 108 - 1011 L

• Structure Dynamics
• Disk Spheroid
• Supported by relatively rapid rotation but in
  the spheroid - random motions.
• 10-20 gas
• On-going star formation in the disks
• Mix of Pop I and Pop II stars

NGC 1232 is located in the constellation Eridanus
. The distance is about 100 million light-years.
The central areas contain older stars of red
color while the spiral arms are populated by
young blue stars and many star-forming regions.
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Barred Spiral Galaxies

• Some spiral galaxies have a bar of stars cutting
  through their centers.
• spiral arms are attached to the ends of the bar
• we call them barred spiral galaxies.

• Some galaxies have disks with no spiral arms.
• we call then lenticular galaxies
• they look like a lens seen edge-on
• They contain less cool gas than normal spirals.

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Elliptical Galaxies

• only have a spheroidal component no disk
  component
• very little ISM which is mostly low-density and
  ionized.
• contain mostly red stars

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Elliptical Galaxies
Properties Mass 105 - 1013 M Diameter 1 -
200 kpc Luminosity 106 - 1012 L

• Structure Dynamics
• Spheroid of old stars with little gas or dust
• Supported by random motions of stars with some
  very slow rotation
• Very little or no gas or dust
• Star formation ended billions of years ago
• See only old Pop II stars

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Irregular Galaxies

• none of the above category neither spiral nor
  elliptical
• appear white dusty with ISM
• have more in common with the disk component of
  spirals
• distant galaxies are more likely to be irregular
• they were more common when the Universe was young

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Irregular Galaxies
Properties Mass 106 - 1011 M Diameter 1 -
10 kpc Luminosity 106 - few x 109 L
Structure Dynamics Chaotic structure lots of
young blue stars Moderate rotation in
Irregulars but very chaotic motions as well.

• Irregulars
• Can range up to 90 gas
• On-going star formation
• Dominated by young Pop I stars
• Dwarf Irregulars
• Very metal poor (lt1 solar)
• Forming stars for the first time only now.

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Groups and Clusters of Galaxies

• Among large galaxies
• most (7585) are spirals
• they tend to associate in loose groups of several
  galaxies

• Some galaxies are associate in clusters.
• contain hundreds of galaxies

• Our Local Group (at least 40) is an example.
• dominated by two large spirals
• the Milky Way
• Andromeda

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LMC

• The Large Magellanic Cloud is one of the closest
  galaxies 50 kpc. The Sagitarrius dwarf is at 24
  kpc.
• It is of fundamental importance for
• - studies of stellar populations
• - interstellar medium
• - dark objects in the Galactic Halo
  through microlensing
• - determinations of the extragalactic
  distance scale

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LMC

• Morphologically
• In the optical wavelength is dominated by the
  bar regions of strong star formation and dust
  absorption.
• - in the near IR is more uniform hint of
  some spiral structure (de Vaucouleurs Freeman
  1973) but with very low contrast.
• The LMC is generally considered an irregular
  galaxy as a result of these characteristics. It
  is in fact the prototype of the class of galaxies
  called Magellanic Irregulars (de Vaucouleurs
  Freeman 1973).

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LMC

• The kinematical properties
• Gas HI maps (Kim et al 1998).
• From discrete LMC tracers
• (Gyuk Dalal Griest 2000).
• A common result from all these studies is
  that the line-of-sight velocity dispersion of the
  tracers is at least a factor of 2 smaller than
  their rotation velocity. This implies that the
  LMC is kinematically cold and must therefore be
  a disk system.

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SMC

• The Small Magellanic Cloud (SMC) dwarf galaxy is
  a satellite galaxy of our Milky Way.
• It contains numerous emission nebulae which are
  clouds of gas that glow red as the hydrogen gas
  they contain is ionised by radiation from nearby
  hot young stars.
• The SMC lies about 185000 light year from Earth
  in the constellation Tucana.

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Regions of the Milky Way Galaxy

• The Milky Way Galaxy consists of a thin disk
  about 100000 light-years in diameter with a
  central bulge.
• The spherical region surrounding the entire disk
  is called the halo.

Sun is in disk 28000 l.y. out from center
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Regions of the Milky Way Galaxy

• Disk
• younger generation of stars
• contains gas and dust
• location of the open clusters
• Bulge
• mixture of both young and old stars
• Halo
• older generation of stars
• contains no gas or dust
• location of the globular clusters