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AGN Luminosity Function as f(z)



 
 
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  #1  
Old December 17th 16, 04:10 PM posted to sci.astro.research
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Default AGN Luminosity Function as f(z)

Hello,

I've so far not found any values for numbers of active galaxies vs
normal galaxies across time. What percentage of galaxies go through an
active phase? I would expect that most galaxies would go through an
active phase due to mergers that spin up the angular momentum in the
central region of the combined galaxy. But I'm looking for any
estimates for percentage of galaxies that go through an active phase
during their history.

Thanks for any direction on existing papers,

rt

  #2  
Old December 18th 16, 10:31 PM posted to sci.astro.research
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Default AGN Luminosity Function as f(z)

On Saturday, December 17, 2016 at 10:10:12 AM UTC-5, wrote:
Hello,

I've so far not found any values for numbers of active galaxies vs
normal galaxies across time. What percentage of galaxies go through an
active phase? I would expect that most galaxies would go through an
active phase due to mergers that spin up the angular momentum in the
central region of the combined galaxy. But I'm looking for any
estimates for percentage of galaxies that go through an active phase
during their history.

Thanks for any direction on existing papers,

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.
  #3  
Old December 24th 16, 11:15 AM posted to sci.astro.research
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Default AGN Luminosity Function as f(z)

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.


  #4  
Old January 7th 17, 10:31 AM posted to sci.astro.research
Steve Willner
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Posts: 1,172
Default AGN Luminosity Function as f(z)

In article ,
writes:
How is z determined for quasars? I assume its from
analysis of emission lines rather than absorption lines.


That's correct.

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


Blazars, but there are very few of them. (I think a thousand or two
versus of order 1M QSOs.) About half of the blazars have known
redshifts.

Our understanding of blazars is that our line of sight is right down
the jet, so relativistic boosting makes the synchrotron continuum
much stronger relative to the emission lines. In the blazars with
known redshifts, lines have been detected, often at a time when
variability has left the jet especially faint.

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.


Generally it's difficult or impossible to observe a QSO host galaxy,
depending on distance and relative brightness. The observed emission
lines come from near the active nucleus and are excited by
ultraviolet and X-ray light from the nucleus.

Seyfert galaxies are thought to be the same phenomenon as QSOs but
with fainter nuclei relative to the host galaxies.

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


Because typical AGN continua resemble a power law, it is impossible
to derive redshifts from them.

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Steve Willner Phone 617-495-7123

Cambridge, MA 02138 USA

 




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