12 Other Galaxies

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12 - Other Galaxies
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Types of Galaxies Spiral
Sa Bulge large Arms tight
Sc Bulge small Arms loose
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Arm Types
M51 - grand design
M101
M33 - flocculent
M - Charles Messiers catalog of fuzzy objects
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Why dont the arms wind up?
Our Sun orbits with P200 Myr The MWG is 14 Gyr
old.. (G? giga billion)
Need 2 different models to explain the 2 type of
arms
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Problem Where DO the spiral arms come from?
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Self-Propagating Star Formation (Stochastic Star
Formation)
Each round of star formation induces more star
formation nearby
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Spiral Density Wave
Gas compression in density wave
New stars exit with old
Stars low density gas
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NOTE dust molecules are coolants in GMCs
4-young stars exit
1-Stars gas ( dust) enter
2-Compression, growth of GMCs, more dust,
molecules, star formation
3-New massive hot stars ionize gas
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Problem(!) Spiral density wave can sustain
itself, once formed. So where did it come from in
the first place?
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Types of Galaxies Barred Spiral
The MWG?
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Types of Galaxies Elliptical Spiral
En where n indicates ellipticity (how
squashed it appears)
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Giant Ellipticals
Dwarf Ellipticals
Wide-angle view of the Virgo Cluster of Galaxies
Close-up view of Leo I galaxy - very nearby MWG
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Hubbles Tuning Fork Classification Scheme Once
thought to represent galaxy evolution -
WRONG! (but astronomers still use terms like
early type and late-type to describe
galaxies.)
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Irregulars.
Small Magellanic Cloud (SMC)
Large Magellanic Cloud (LMC)
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Clusters of Galaxies
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M31 Andromeda Galaxy
M32
NGC205
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M31
NGC185
NGC205
M32
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M33
NGC6822
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Cepheids in galaxies
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Ladder of Extragalactic Distance Scale
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Hercules Cluster - Irregular - Lots of Ss
Coma Cluster - Regular - Mostly Es
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Colliding Galaxies
The Antennae
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21 cm map (H I)
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Collisions Mergers.
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Galaxy Cannibalism
Interactions can initiate the spiral density
waves!
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Flat Rotation Curves Dark Matter
Flat rotation curves require lots of dark
matter in the halos..
It isnt just a problem for the MWG!
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1920s 1930s - Humason Hubble discover the
Expansion of the Universe!
Hubble Flow
Hubble Law v H0d
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H072 8 km/s/Mpc
A LOT of work has been expended in the past 50
years to measure H0 precisely. Values ranged from
50-100 km/s/Mpc!
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Problem How do galaxies form evolve?
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Top-Down Galaxy Formation
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Bottom-Up Galaxy Evolution (mergers dominate
the process)
Remember this one?
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The Hubble Deep Field (HDF)
HDF detail
looking far away looking back in time
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Ultra-Deep Field (UDF)