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View Full Version : Why do many AGNs seem to have just one jet?



Nereid
2006-Aug-29, 11:46 PM
DRAGNs (http://www.jb.man.ac.uk/atlas/), by definition, have two.

But 3C 273 (http://www.astr.ua.edu/keel/agn/3c273.html) and M87 (http://www.astr.ua.edu/keel/agn/m87jet.html) (to give just two examples) have just one.

Why?

Blob
2006-Aug-30, 12:10 AM
..many radio-loud AGN objects, particularly FR--II radio galaxies and radio-loud quasars as defined later, display only one jet. It is very difficult to believe that only one-sided jets are created in symmetrical double radio sources. In fact, it is believed that there are two jets, but due to the relativistic bulk motion of the flow within the jet, there are significant beaming effects due to aberration (Blandford, 1990; Begelman et al., 1984). This is believed to be the reason why counter-jets are not observed on the radio maps.

http://cosmos.astroscu.unam.mx/~sergio/phdthesis/phdlatex2html/node10.html


However, the Roger Blandford twisted-magnetic-field model , although an attractive model, does have problems...


Title: Shedding New Light on the 3C 273 Jet with the Spitzer Space Telescope
Authors: Y. Uchiyama, C. M. Urry, C. C. Cheung, S. Jester, J. Van Duyne, P. Coppi, R. M. Sambruna, T. Takahashi, F. Tavecchio, L. Maraschi

Researchers have performed infrared imaging of the jet of the quasar 3C 273 at wavelengths 3.6 and 5.8 microns with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope.
When combined with the radio, optical and X-ray measurements, the IRAC photometry clearly shows that the optical emission is dominated by the high-energy component of the jet, not by the radio synchrotron component, as had been assumed to date.
The high-energy component may be due to a second synchrotron component or to IC scattering of ambient photons. In the former case, they argue that the acceleration of protons exceeding 10^16 eV or possibly even to 10^19 eV would be taking place in the jet. In contrast, the IC model, into which highly relativistic Doppler beaming has to be incorporated, requires very low-energy electrons (~ 1 MeV). The present polarisation data in the radio and optical would favour the former interpretation in the case of the 3C 273 jet.
Sensitive and detailed measurements of optical polarisation are important to establish the radiation mechanism responsible for the high-energy emission. The present study offers new clues as to the controversial origin of the X-ray emission seen in many quasar jets.

Read more (http://arxiv.org/PS_cache/astro-ph/pdf/0605/0605530.pdf) (294kb, PDF)

madman
2006-Aug-30, 02:47 AM
there was a baut news story a few months back on the subject of the jet of 3c273

http://www.universetoday.com/2006/06/20/distant-quasars-are-natural-particle-accelerators/

in the comments section i've added a composite image that also shows the quasar at top left (where the image alignment lines merge).

note the large gap between the quasar and the first visible (xray) section of the jet.

could this harbor a neutral flow with a very minimal intensity?...or a very bright gamma flow that cannot be seen...since we don't have a gamma shot yet?

Ken G
2006-Aug-31, 04:09 AM
Another way to look at Blob's answer is that if you have a particular Lorentz factor (gamma) in a flow, then isotropic emission kind of gets focused into a forward angle of size 1/gamma, due to the way angles get focused into the forward direction (aberration). So the backward jet is there, but is busy beaming its light in the direction away from us. Of course, that simple analysis applies to a flow in a straight line, whereas presumably the particles are spiraling around magnetic fields that in turn may be convoluted, so the appropriate geometry is constantly debated.

madman
2006-Aug-31, 05:37 PM
thanks for the explanation Ken G.

"plain" aberration did seem to sound a bit weak as a reason.

but also...i'm not sure if i can believe the lorentzian answer either.
in the example of m87...i think it's fairly perpendicular to our sight.

...if you want to see a multiwavelength composite image of it (and maybe consider the possibility that the jet may have a strong helical flow?...and a lot of other crazy things)..come and check out my "galactic smoking gun" thread.

http://www.bautforum.com/showthread.php?t=30009

Ken G
2006-Aug-31, 06:07 PM
but also...i'm not sure if i can believe the lorentzian answer either.
in the example of m87...i think it's fairly perpendicular to our sight.

I don't know anything about M87, but note that it's easy to get fooled by perspective effects. For example, sun beams are always exactly parallel, but they never look that way coming through a cloud. So the jet could be coming toward us and not look like it is. Futhermore, there's the issue of the particles spiralling around a convoluted field, so there can be particles coming straight at you even when the overall jet doesn't appear to be. Perhaps all these issues contribute to one jet being much more visible than the other. By the way, helical jet geometries are often considered as being perfectly reasonable, presumably because of twisting of the fields.

madman
2006-Sep-01, 05:41 AM
Ken G

Perhaps all these issues contribute to one jet being much more visible than the other.

the point that is being made by the authors of the lorentzian answer is that the light from the other jet is being completely extinguished...or rendered invisible along our sight line.


it is just as reasonable (imho) to consider that this is not always happening..and that in a few instances jets occur in a monopole fashion.

it seems that a reason has been generated to explain an effect that perhaps goes against theory...rather than an attempt to consider the possibility of monopolar jets.

Ken G
2006-Sep-01, 08:31 AM
I certainly don't know how one could rule out that possibility for some jets.

madman
2006-Sep-01, 08:48 AM
cool.

it's just that sometimes M (mainstream) doesn't make it clear how open minded they are.

Ken G
2006-Sep-01, 09:23 AM
I think it is a case of favoring what seems to work best in most cases, and subconsciously extending that to an assumption about all cases. It reminds me of a joke-- a man at a conference in a foreign land sees a squirrel and says, "hey, the squirrels are black here". His friend, a lawyer, says "actually, you can only conclude that that squirrel is black". "On the contrary", says a second friend who is a logician, "you can only say that that side of that squirrel is black."

RussT
2006-Sep-02, 08:48 AM
Ken G


the point that is being made by the authors of the lorentzian answer is that the light from the other jet is being completely extinguished...or rendered invisible along our sight line.


it is just as reasonable (imho) to consider that this is not always happening..and that in a few instances jets occur in a monopole fashion.

it seems that a reason has been generated to explain an effect that perhaps goes against theory...rather than an attempt to consider the possibility of monopolar jets.

I think that because we have seen some AGN's with the 2 jets perpendiular to the plane, that it is just easier to go with what is already known, than to come up with a whole new way that only one jet could be shown to be produced.

I also think we need to know more about AGN/Quasar evolution to solve this.

In other words, when galaxies get to the stage where the core is sufficiently 'ready' for the jets to turn on...does it go AGN then turn into a Quasar, then go back to AGN? OR do the jets turn on so powerfully right off the bat, that we see a Quasar and then it slows to an AGN and then to a quiet core?

Or as madman and I have suggested (HE did it first and showed in another thread where he had done it previously), that Quasars are AGNs but with their jets pointed almost directly at our line of sight?

http://www.bautforum.com/report.php?p=812789

madman
2006-Sep-02, 09:23 AM
did i?.....do you mean 3c273?

also...you linked to a "report this thread page".....so i'm unsure as to what you are referring to?

RussT
2006-Sep-02, 11:30 AM
did i?.....do you mean 3c273?

also...you linked to a "report this thread page".....so i'm unsure as to what you are referring to?

http://www.bautforum.com/showpost.php?p=766814&postcount=6

Ah, here it is. When I clicked on the link your first response in this thread, there it said you had done something in the 'comments' at the bottom of that page, and that is where I found this. From June/06.

I put the link that I posted on the other thread in so you could see my explanation was basically the same as yours and clarify any parts that you wanted to.

Ken G
2006-Sep-02, 02:06 PM
Or as madman and I have suggested (HE did it first and showed in another thread where he had done it previously), that Quasars are AGNs but with their jets pointed almost directly at our line of sight?


That wouldn't be enough to explain the differences. Remember, we don't just see the jet, we also see the galaxy, and the main difference about the galaxy is how far away it is. Generally, quasars are much farther away than AGNs. It is conceivable that this is because you can see quasars much farther away (Malmquist bias), but I would imagine that possibility has been examined and discarded. The general conclusion is that quasars don't exist any more, but AGNs do.

RussT
2006-Sep-04, 09:34 AM
That wouldn't be enough to explain the differences. Generally, quasars are much farther away than AGNs. It is conceivable that this is because you can see quasars much farther away (Malmquist bias), but I would imagine that possibility has been examined and discarded. The general conclusion is that quasars don't exist any more, but AGNs do.

[Remember, we don't just see the jet, we also see the galaxy, and the main difference about the galaxy is how far away it is.]

I was under the impression that the techniques for 'filtering' or 'extinguishing'
the extreme brightness/magnitude of a Quasars main light sequence was pretty new and very complicated. So, doesn't that bring into question, after this kind of procedure, can they still get a redhift reading 'from the galaxy'?

Ken G
2006-Sep-04, 02:46 PM
Getting redshifts from quasars is quite straightforward, despite the reticence of a tiny minority of scientists to accept the noses on their faces. Quasars, not their jets, emit line radiation with large and obvious redshifts.

Nereid
2006-Sep-06, 02:42 PM
If you google on type II quasars (or type 2 quasars), and read some of what it serves up, you may find yourself spending an interesting hour or so ...

These objects fit rather nicely into a slot in the unified AGN model (http://www.mssl.ucl.ac.uk/www_astro/agn/agn_unified.html).

Given the model's considerable success, the discovery of a mono-polar jet, coming from an AGN, would be exciting indeed!