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GalaxiesGalaxies
Island Universes
1414Copyright – FORS1 VLTI, European Southern Observatory
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Ellipticals
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Ellipticals
• Huge• No gas.• No dust.• No young
stars.• Nothing but
old stars.– Random
orbits.
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M 87 Copyright – Anglo-Australian Telescope Board
Copyright - HST
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Spirals
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Spirals
• Like Milky Way.• Disks and
bulge.• Young stars
and old.• Gas and dust.• Stars forming.• Stars dying. M81 and M82 – Copyright R. Gendler
1414M63 Copyright – S. Miyazaki, Suburu
1414NGC1365 Copyright – VLT
1414M31 The Andromeda Galaxy Copyright – Jason Ware
Copyright – S. Miyazaki, Suburu
1414M33 – Copyright NOAO
1414M51 - Copyright HST
John P. Gleason
1414NGC 4314
1414NGC 891 – Copyright J.C. Barentine, NOAO
NGC 891 – Copyright WIYN
1414Sombrero Galaxy – Copyright P. Barthel VLT
M10 – copyright Credner and Kohle
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NGC 4526
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Irregulars
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Nearby Galaxies
• Cepheids.• Period.• Luminosity
abs. mag.• Know app. Mag• Get Distance.
10pc
distancelog5 10Mm
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Groups
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The Local Group
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Clusters
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The Virgo Cluster
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Distant Galaxies
• Can’t see individual stars.• Can use nearby galaxies to get
distances to further galaxies.• Distance ladder:
– Parallax nearby stars– Nearby stars H-R diagram– H-R diagram distant stars (variables)– Variable stars nearby galaxies– Nearby galaxies ?
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21cm Radiation
• Neutral hydrogen (HI) gives off radiation at 21cm.
Milky Way HI emission – Copyright J. Dickey
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Extragalactic HI
• Observe HI in other galaxies.• Measure wavelength of 21 cm radiation.• Get velocity away from us.
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Hubble’s Law
• Measure the velocity of every galaxy.
• Nearly all are redshifted.
• Use Cepheids to measure distances to nearby galaxies.
• Result: The faster it’s moving, the farther away it is.DH v
distance velocity
o
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Map the Universe• V = HoD
• If you know Ho:
• Measure v• Get D• Find:
VoidsWalls
Clusters
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Homework #12Homework #12
• Read: Bennett Ch 22.1 – 22.4• Do Ch22:
– Problems: 1, 6, 9, 12– Math folks substitute problem 18 for 9 and
12.