Review

#02

Ellipticals are similar to our Milky Way halo in several aspects: they contain old stars, these have random orbits, and there is little gas or star formation. Ellipticals however are also repositories of hot gas that emit X-rays, which our halo does not have.

#05

Standard candles are objects with known luminosities associated with particular kinds of behavior (such as Cepheid pulsators, or SN explosions). As such, we can directly relate apparent brightness to distance for the known luminosity.

#09

We can measure the rotational speeds of galaxies, using the doppler effect. The Tully-Fisher relation connects these speeds with the luminosity of the galaxy as whole, so that one can infer distances.

#11

Active galaxies are usually much more luminous, and most of their luminosity comes from a fairly compact central region.

#13

Seyferts are spiral galaxies with unusually bright central cores. They may be X-ray bright or infrared bright, and they show broad spectral lines, indicating high speed motions in their cores.

#16

Large redshifts.

#17

Distances require knowledge of the hubble constant, whereas redshift is a directly measured quantity having to do with the spectral displacement of some regular feature (such as a spectral line). So distances will ``change'' from time to time, based on improvements in knowing the Hubble constant, but redshifts will not.

#19

A central supermassive black hole surrounded by a bright accretion disk, often accompanied by a central jet outflow of gas.