Astro 1050 Fri., Nov. 14, 2004
| Today: Chapter 13, Galaxies | |
| Family of Galaxies | ||
| Classification | ||
| Properties of Galaxies | ||
| Distance; The Hubble Law | ||
| Size and Luminosity | ||
| Mass (including Dark Matter) | ||
| Evolution of Galaxies | ||
| Clusters | ||
| Mergers | ||
Types of Galaxies (pg. 254-255)
| Spirals | ||
|
Sa Sb Sc (large nuclei Þ small nuclei) (little gas,dust Þ lots of gas, dust) |
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| SBa SBb SBc (as above, with BARS) | ||
| Ellipticals | ||
| E0
E1 E2 E3 E4 E5 E6 E7 (spherical) (highly elliptical) |
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| Irregulars | ||
| The nuclear bulge is population II (old objects) | |
| So the Sa – Sc sequence is consistent
with little gas Þ more gas |
Irregular Galaxies: Magellanic Clouds
| 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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The Hubble Law using galaxies with visible Cepheid variables.
Hubble Law Example
vr = H0 d
with H0=0.5 (mile/hr)/mile
Hubble Law Example
vr = H0 d
with H0=0.5 (mile/hr)/mile
Hubble Law Example
vr = H0 d
with H0=0.5 (mile/hr)/mile
Hubble Law Example using relative vr and relative d
The Hubble Law using
secondary distance indicators
Ho = 72 ±8
km/s/Mpc
| Galaxies live in clusters | ||
| Rich clusters: thousands of galaxies | ||
| Poor clusters: Fewer than a thousand | ||
| 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 | |||
| 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 | ||
| Joshua Barnes (Hawaii) and the Space Telescope Science Institude provide a simulation of the Antenna Galaxies: http://imgsrc.stsci.edu/op/pubinfo/pr/1997/34/images/anima.mov | ||
Interacting Galaxies: The Antennae
Interacting Galaxies: Cartwheel
Simulation of the Cartwheel Encounter
| From the Space Telescope Science Institute which also provided the Cartwheel image in the textbook: | |
| http://imgsrc.hubblesite.org/hu/discoveries/striking_encounters/graphics/cartwheel.mpg |
Evidence for “Hierarchical” Galaxy Formation from the Hubble Deep Field
| Movie simulation of galaxy formation via assembly of small pieces (courtesy of Space Telescope Science Institute): http://imgsrc.stsci.edu/op/pubinfo/mpeg/galaxies.mpg |
| Family of Galaxies | ||
| Classification | ||
| Properties of Galaxies | ||
| Distance; The Hubble Law | ||
| Size and Luminosity | ||
| Mass (including Dark Matter) | ||
| Evolution of Galaxies | ||
| Clusters | ||
| Mergers | ||