Transcript Class 22 galaxy formation Collisions of galaxies. Formation of galaxies.

Class 22 : Galaxy collisions &
galaxy formation
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Collisions of galaxies.
Formation of galaxies.
I : Collisions of galaxies
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Galaxy collisions are comparatively
common (and spectacular!).
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Major collision…
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Collision of 2 big galaxies.
Quite rare.
Minor collision…
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Collision of a large galaxy with a small
“dwarf” galaxy.
Very common!
Movies of galaxy merger
simulations…
What happens when two
galaxies pass close to
one another?
Chris Mihos & Sean Maxwell
Flyby…
Notice the “tidal tails”
that are thrown off
and the disorganized
“lump” at the center.
Chris Mihos & Sean Maxwell
The Antennae Galaxy
The Cartwheel Galaxy
Cartwheel Simulation
Chris Mihos & Sean Maxwell
Fate of the Milky Way?
Centaurus A shells
• Cen A is a
peculiar galaxy
with strong
radio emission.
• Star shells
are a common
sign of recent
mergers.
CTIO
Minor (satellite) merger
• Most mergers are
like this one: big guy
eats little guy.
• Dumps a lot of gas
and dust into big
galaxy.
• Small galaxy
completely disrupted.
Chris Mihos & Sean Maxwell
Galaxy Harassment
• Multiple small
interactions over time
in clusters can tear
galaxies apart.
N-body shop, U Washington
Internal evolution
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Galaxy collision can drive “internal evolution”
of galaxies…
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Rapid star formation
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Galactic collisions make gas clouds collapse and turn
into stars.
Makes galaxy look blue (since there can be many
young, hot stars).
Quasar activity
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Galactic collision drives gas into center of galaxy.
Gas can rain onto central massive black hole and
produce tremendous amounts of energy…
More about this possibility soon…
II : Galaxy formation
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How did galaxies form?
In the beginning…
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The BIG BANG!
Universe started off very hot, and very
uniform (matter smoothly filled all space).
BUT, there were very small fluctuations in
the uniform distribution of matter…
Gravity caused fluctuations to grow.
What happened next?
Nowadays, can study this process using
computer simulations…
Simulation from the “Virgo
Consortium”… (CDM)
Zoom in on a forming galaxy
cluster (Virgo Consortium)
This movie
zooms in on one
patch of a larger
simulation where
we know that a
galaxy cluster is
about to form.
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“Bottom-up” formation scenario…
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All driven by gravitational collapse.
Some small things form first.
Collisions/mergers cause bigger things to
grow…
Dwarf galaxies  galaxies  galaxy clusters
 superclusters and so on.
Las Campanas
Redshift survey
Sloan Digital Sky Survey