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A Comparison of Active Galactic Nuclei
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| Property |
Quasars |
Seyfert Galaxies |
Radio Galaxies |
BL Lac Objects
|
| Galaxy Type |
Spiral & elliptical |
Spiral |
Giant elliptical & Elliptical |
Elliptical
|
| Appearance |
Compact, blue |
Compact bright nucleus |
Elliptical galaxy, halo or lobes of RF |
Bright, starlike |
Maximum
Luminosity |
100-1000 x Milky Way |
Comparable to brightest spirals |
Strong RF from 0.1-10
times optical luminosity |
10,000 x Milky Way |
| Continuum Spectrum |
Non-thermal |
Non-thermal |
Non-thermal |
Non-thermal |
| Emission Lines |
Broad and Narrow |
Broad and Narrow |
Rare but Broad and Narrow |
Very Weak |
| Absorption Lines |
Yes, redshift often less than for emission lines |
None |
Yes |
None |
| Variability |
Days to weeks |
Days to weeks |
Short as Days |
Short as hours |
| Radio Source? |
Some |
Weak (from nucleus) |
Strong (jets & lobes) |
Weak (from nucleus) |
| Redshifts |
z > 0.5 |
z ~ 0.05 |
z < 0.05 |
z ~ 0.1 |
| Jets |
Some |
Some |
Often |
Perhaps aimed at us |
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