Download The Relative Ages of M5 and Pal 4/Eridanus from their

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.
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.
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
The Hubble Classification
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
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.
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 edgeon

They contain less cool gas
than normal spirals.
Elliptical Galaxies



only have a spheroidal component; no disk
component
very little ISM, which is mostly low-density and
ionized.
contain mostly red stars
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
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
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 (<1% solar)
Forming stars for the first time
only now.
Groups and Clusters of Galaxies


Among large galaxies…
• most (75–85%) 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
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
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).
LMC
Type
RSG
Age
Young
Velocity
dispersion
(km/s)

15

The kinematical properties:
Gas – HI maps (Kim et al 1998).
From discrete LMC tracers:
(Gyuk, Dalal & Griest 2000).
HII
Young
6
Carbon
stars
Young
15
PNs
Intermediate
20
LPV
Old
33
GC
Old
30
A common result from all
these studies is that the lineof-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.
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 185,000 light year from
Earth, in the constellation Tucana.
Regions of the Milky Way Galaxy
•The Milky Way Galaxy consists of a
thin disk about 100,000 light-years
in diameter with a central bulge.
•The spherical region surrounding
the entire disk is called the halo.
Sun is in disk,
28,000 l.y. out
from center
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