On Sunday, December 18, 2016 at 1:31:41 PM UTC-8, wrote:
On Saturday, December 17, 2016 at 10:10:12 AM UTC-5, wrote:

Jeanta, thanks for these links. Lots to read. Duty cycle makes good
sense.

It occurs to me that there is a very basic issue I'm not sure I
understand. How is z determined for quasars? I assume its from
analysis of emission lines rather than absorption lines.

Is there a class of quasar where the z value is unknown due to the light
being featureless?

I guess I'm confused since if the quasar is light from some process
around a BH within a galaxy, then I'd expect that light to blind
observation of stellar emissions nearby, from which a z value could be
attained.

Does z come somehow from the continuum from the BH light, or, ????

Thanks again for the references,

rt

The magic word is "duty cycle".

Here are two articles from 2000 that give a good background:
"Evolution of QSOs and other Active Nuclei",
http://pages.astronomy.ua.edu/keel/g...qsoevolve.html
"Fueling the AGN", esp Section 8,
https://ned.ipac.caltech.edu/level5/..._contents.html
This paper, Shankar+ (2010), arXiv version:
https://arxiv.org/abs/1004.1173, shows how much work was done in
just a decade; check the papers which cite this for more recent
work.

Hope this helps.