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<p>
<center><table cellpadding=10 border=10 bgcolor=aqua><tr><td><center>
<h2>Normal Galaxies<p></h2><h3>
<center>Chapter 24, Galaxies, Building Blocks of the Universe</td><td>
<img width=500 
src="http://hendrix2.uoregon.edu/~imamura/123/lecture-3/galaxiesHST.jpg">
</td></tr></table></center>
<h3>
<p>
Galaxies are clusters of stars, gas, dust, and dark matter whose emission 
is dominated by the light from its stars; their spectra are sum of the 
individual stars. Galaxies 
serve as markers in our study of the structure of the
Universe. They are interesting in their own right, however. 
Hubble developed the 
following <i>morphological</i> based on their appearance)
classification scheme for galaxies.
Basically, Hubble formed the classes of 
<a href="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/NGC4881.gif">ellipticals</a>,
<a href="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/NGC4639.gif">spirals</a>, and
<a href="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/NGC1365.gif"> barred spirals</a>.
In addition, there are galaxies which have disks but no arms, S0s
(lenticulars), and amorphous looking things which he referred to as 
<a href="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/ngc2363.gif">Irregulars</a>.
Schematically, the <font color=magenta>
<i>Hubble Tuning Fork</i> </font> diagram looks like
<p>
<center>
<img src="http://hendrix2.uoregon.edu/~imamura/123/lecture-2/
HubbleTuningFork.jpg">
</center>
<p>
The preceding is <font color=magenta>not</font> 
thought to be an evolutionary scheme. There, however, appears to be 
evolution between the different Hubble classes as a result of collisions 
between galaxies. 
The Milky Way 
galaxy is usually classified as
an <i>SBb</i> galaxy in the Hubble scheme.
<p>
Despite the fact that the Hubble Sequence is based only on the 
appearance of galaxies (morphology of galaxies), several 
physical properties 
of galaxies vary smoothly along the sequence. We have, 
<p>
<h3>
<pre>
little gas and dust <----------------------> lots of gas and dust
mainly Pop II stars <----------------------> Pop I & II stars
Reddish <----------------------------------> Bluish
little ongoing star formation <------------> star formation
large bulge <------------------------------> small bulge
                      tight arms <---------> loose arms
</pre>
</center>
<p>
<p><hr>
<p>
<center>
Origin of Elliptical and Spiral Galaxies
</center>
<p>
The basic idea is that either an elliptical galaxy or spiral galaxy
will form depending upon when star formation occurs in the galaxy formation
process. Galaxies are thought to form from the collapse of low-density gas
clouds. If the gas turns into stars during the early stages of the 
process, then we essentially have a bunch of BBs 
collapsing to form the galaxy. Because
stars are small and they are far apart, they don't collide 
in the formation process. This allows the stars 
to maintain roughly their initial <i>shape</i> and to settle into a 
roughly spherical form. In this case, they  become elliptical galaxies.
<p>
If the gas does not turn into stars quickly, 
then we have a system of collapsing gas clouds. The gas clouds are 
much larger than are stars and collide much more readily during 
the formation stage. The collapsing material thus <i>runs</i> into 
opposing material as it tries to pass through the equatorial plane
(for an analogous situation, consider the 
<a href="http://hendrix2.uoregon.edu/~imamura/122/images/sform_diag.jpg">
star formation process</a>). The collisions do not allow
the collapsing material to pass through each other and the material is forced
to settle into a disk. After the disk forms, star formation begins in 
earnest and a spiral galaxy is produced. 
<p><hr>
<p>
<center>
Distribution of Galaxies In Space
</center>
<p>
<center>Extragalactic Distance Ladder</center>
<p>
<center>
Clustering Scales
</center>
<p><table cellpadding=10 border=10 bgcolor=aqua><tr><td>
<img src="http://hendrix2.uoregon.edu/~imamura/121/lecture-3/jworlds.jpg"></td>
<td><h3>Solar System</a> ===> ~ 0.5 light day</td></tr>
<tr><td>
<img src="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/NGC4639.gif"></td>
<td><h3>Galaxy Sizes (NGC 4639)</a> ===> 0.1 Mly to 1 Mly</td></tr>
<tr><td>
<img src="http://hendrix2.uoregon.edu/~js/ast123/lecture-3/M31.gif"></td>
<td><h3>Local Group (Andromeda, M31) ===> ~ 3 Mly </td></tr>
<tr><td>
<img src="http://hendrix2.uoregon.edu/~soper/ImGalaxies/virgo.jpg"></td>
<td><h3>Clusters (Virgo cluster) ===> ~ 10 Mly </td></tr>
<td></td>
<td><h3>Clusters of Clusters (Super-Clusters) ===> ~ 300 Mly</td></tr>
<tr><td>
<img src="http://hendrix2.uoregon.edu/~imamura/123/lecture-3/slice.jpg"></td>
<td><h3><i>Great Wall</i> and <i>Voids</i>
===> 600 & 300 Mly (~ 0.6 and 0.3 Bly)</td></tr></table>
<p><hr><p>
<table cellpadding=10 border=10 bgcolor=aqua><tr><td>
<h3><center>Redshift, Look-Back Time, and Distance</center><p>
Because light travels with a finite speed, c = 300,000 kilometers per second,
the light which we receive from distant objects must have left the objects
sometime in the distant past.  In the table to the right (taken from the 
text), we show the relationship between the redshift, current distance of
the object and the <i>look-back time</i> for the object. Note that the 
Universe was smaller when the light left the distant objects.
<td><table bgcolor=pink cellpadding=10 border=10
<tr><td><h3>Redshift</td><td><h3>v/c</tde><td><h3>Distance</td>
<td><h3>Look-Back Time</td></tr>
<tr><td><h3>0.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.010</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.025</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.050</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.100</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.200</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.250</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.500</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>0.750</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>1.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>1.500</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>2.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>3.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>4.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>5.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>6.000</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>10.00</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>50.00</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>100.0</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
<tr><td><h3>infinity</td><td><h3>0.000</td><td><h3>0 Ly</td><td><h3>0 y</td></tr>
</table>
</td></tr></table>
<p><hr><p>
<table bgcolor=aqua cellpadding=10 border=10><tr><td>
<img src=
"http://hendrix2.uoregon.edu/~imamura/123/lecture-1/cmbcobewmap.jpg"></td>
<td><h3><center>Structure Formation</center><p>
There is large scale structure in the Universe. An important problem is
the question of <i> Where and when did this structure form?</i>
Although the cosmic microwave background radiation (CMBR) is very 
<i>smooth</i> ---> the Universe was very smooth
at the time of formation of the CMBR (~380,000 years after the birth of the
Universe), the Universe did show considerable structure even at the time
of the formation of the CMBR.
This means that the Universe started to generate 
the currently observed structure  of the Universe
in the time before the formation of the CMBR (the 
Epoch of Recombination)
(<a href="http://hendrix2.uoregon.edu/~imamura/123/lecture-3/
BigBangtillNOW.flv"/>
computer simulation of structure formation</a>).</td><tr></table>
<p><hr>
<p>
<center>Galaxies in Collision</center>
<p>
Galaxies are often times found in rich clusters and because the Universe
was smaller in the past, collisions between galaxies are likely to have been
more important in the past. Collisions still occur today and will occur in 
the future. For example,
<table cellpadding=10 border=10><tr><td>
<img width=400 src="antennae_1.jpg"></td>
<td><a href="antennae_simulation.mp2">
<img width=500 src="antennae_hst_collision_2.jpg"></a><p><center>
Antennae Galaxy</center></td>
</tr></table></center>
<table cellpadding=10 border=10><tr><td>
<a href="CartWheelEvol.mp2">
<img width=500 src="cartwheel.gif"></a>
<p><center>Cartwheel Galaxy</center></td>
<td><img width=450 src="ngc-4676-when-mice-collide.jpg">
<p><center>
Mice Galaxy</center></td>
</tr></table></center>
<p><hr><p>
<table cellpadding=10 border=10><tr><td><h3><center>Milky Way and Andromeda
Collision<p></center>The Milky Way and Andromeda (distance 2.1 million light
years) are the largest galaxies in the <i>Local Group</I>. Andromeda is 
approaching the Milky Way and is expected to interact in ~2-3 billion years.
The first collision will not disrupt the galaxies but they will re-interact
eventually merging in less than 10 billion years.</td><td>
<a href="andromedaandmilwy.mpg"><img src="M31.gif"></a>
</td></tr></table></center>
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