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1
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- Today: Chapter 13,
Galaxies
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2
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- Family of Galaxies
- Properties of Galaxies
- Distance; The Hubble Law
- Size and Luminosity
- Mass (including Dark Matter)
- Evolution of Galaxies
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3
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4
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5
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6
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- Spirals
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Sa
Sb
Sc
(large
nuclei
Þ small nuclei)
(little gas,dust Þ lots of gas,
dust)
- SBa
SBb
SBc (as
above, with BARS)
- Ellipticals
- E0 E1 E2 E3 E4 E5 E6
E7
(spherical)
(highly elliptical)
- Irregulars
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7
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- The nuclear bulge is population II
(old objects)
- So the Sa – Sc sequence is consistent with
little gas Þ more gas
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8
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9
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10
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- Distance
- Use Cepheid Variables for close objects
- Other objects for which Absolute Magnitude is known:
- Supernova
- Planetary nebula in certain emission lines
- Use “Hubble Law” for more distant objects
- (Correlation of distance with radial velocity)
- Diameter and Luminosity
- Obtain from angular size and magnitude, combined with distance
- Mass
- Rotation curves
- Velocity dispersion
- 90 to 99% of mass is
“dark matter”
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11
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12
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13
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14
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15
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16
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17
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18
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- Galaxies live in clusters
- Rich clusters: thousands of
galaxies
- Poor clusters: Fewer than a
thousand
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19
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20
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- Galaxies live in clusters
- Rich clusters: thousands of
galaxies
- Poor clusters: Few than a
thousand
- Fundamental difference between stars and galaxies:
- Stars live isolated lives:
- They are much smaller than distance between them
- They virtually never collide
- Galaxies are not isolated
- They are only slightly smaller than the distances between them
- The can (and do) collide, and interact with gas within clusters
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21
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- Stars pass “through” each other, but orbits around galaxy
disrupted
- Gas clouds collide
- Gas stripped away from stars
- Collisions cause bursts of star formation
- Ellipticals may be those galaxies which have suffered collisions
- Spirals may be those galaxies which have not suffered collisions
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22
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23
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24
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- Joshua Barnes: http://www.ifa.hawaii.edu/faculty/barnes/transform.html
- John Dubinksi:
- http://www.cita.utoronto.ca/~dubinski/nbody/
- Chris Mihos:
- http://burro.astr.cwru.edu/models/models.html
- Bob Berrington (Wyoming):
- http://physics.uwyo.edu/~rberring/
- There are others…
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25
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26
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27
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- Movie simulation of galaxy formation via assembly of small pieces
(courtesy of Space Telescope Science Institute):
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28
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- Family of Galaxies
- Properties of Galaxies
- Distance; The Hubble Law
- Size and Luminosity
- Mass (including Dark Matter)
- Evolution of Galaxies
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Notes
