Lecture 21
Radio sources, jets, and modern surveys
Tuesday August 5, 2008
Slides on Angel
Concepts:
- Inclination: High inclination sources viewed from edge (see through torus, narrow lines only), moderate inclination sources viewed from above (see broad lines), low inclination viewed down jet (featureless optical spectrum)
- Relativistic beaming: Radiation in jet concentrated in direction of motion, so acts more like flashlight than lightbulb
- Radio morphology: High inclination objects tend to be lobe-dominated, low inclination objects core-dominated, and moderate inclination objects in between
- Survey type: SDSS and FIRST are wide and shallow surveys, covering a large fraction of the sky to moderate faintness. Contrast with the Hubble Ultra Deep Field, a narrow/deep survey that looks at a very small region of the sky but can see extremely faint objects
Vocabulary:
- Synchrotron radiation: Electrons spiraling in magnetic field emit synchrotron radiation. Spectrum is featureless, non-thermal (power-law)
- SDSS: Sloan Digital Sky Survey, the best modern optical survey. Both photometric (image) and spectroscopic data for hundreds of thousands of objects
- FIRST: Radio counterpart to SDSS, covers similar area and to complementary depth
Activity:
Looked at optical spectra and radio images of 9 sources, categorized them by optical spectra
into narrow-line, broad-line, or featureless, and by radio structure into lobe-dominated, in-between,
or core-dominated. Saw that optical spectral properties were related to radio morphology, and
deduced inclination of the sources based on understanding of unification models.
Random link:
Excerpt from Hubble news release titled "Globular Clusters Tell Tale of Star Formation in Nearby Galaxy Metropolis"
Globular star clusters, dense bunches of hundreds of thousands of stars, have some of the oldest surviving stars in the universe. A new study of globular clusters outside our Milky Way Galaxy has found evidence that these hardy pioneers are more likely to form in dense areas, where star birth occurs at a rapid rate, instead of uniformly from galaxy to galaxy.