# The quasar in NGC 7319

1. Mar 16, 2006

### Nereid

Staff Emeritus
[Moderator note: this thread has been created by splitting out posts related to 'the quasar "in" NGC 7319', in the quasar anomaly thread.]
Ah, the quasar that shines through a 'hole' in a galaxy!

Those galaxies, they sure look 'solid', don't they? Who'd'a thunk that you could see right through one?

Of course, the breathless prose of a PR from a marketing department aside, it's interesting, but not at all unexpected.

Consider: Maffei 1 and Maffei 2; Dwingeloo 1; the Lockman hole; and Bill Keel's work (for example).

Last edited: Mar 18, 2006
2. Mar 16, 2006

### ratfink

http://www.pickingjobs.com/job.php?jobid=38
Hi Nereid,
Thanks for the links, but there seems to be a problem. Whenever I click on them I get galaxies that have absolutely nothing to do with the one with the Quasar in the middle. I would be ever so grateful if you could check them and provide the real link that shows that the Burbridge galaxy has a hole in it with the quasar behind.
Thanks. I did find this one though

3. Mar 17, 2006

### Nereid

Staff Emeritus
One step at a time, ratfink.

The first thing to establish is that the disks of spiral galaxies are not (uniformly) opaque. Here in our solar system, we are in such a disk, yet we can not only see out (all directions more than ~5o above the galactic plane, except for towards the bulge, and a few dusty regions), but right through the disk (even amateurs can take images of the Maffei group). Further, even wrt the ubiquitous hydrogen, there are 'holes' - the Lockman hole being one; if you check out the EUV Explorer, you'll find that it detected objects way, way beyond the local region of the Milky Way, despite the Lyman limit.

This shows that it is quite possible to see through the disk of a spiral galaxy, so that finding a quasar 'in' a spiral arm isn't verboten.

Next, if you read the Arp and Burbidge paper, you'll see that the QSO spectrum has absorption lines in it ... consistent with gas in the galaxy. Now this by itself doesn't rule out the QSO being 'in' the galaxy, it does rule it out of being 'in front of' the galaxy (and, BTW, AFAIK, no quasars along lines of sight through galaxies have been observed to have no such absorption lines).

So what's left, in terms of convincing observations supporting the interpretion that the QSO is 'in' the galaxy (and not far, far in the background)? Nothing; ergo, the QSO is where its redshift 'says' it is.

4. Mar 18, 2006

### ratfink

Being possible is not the same as there being a hole in this particular galaxy. Has anyone repeated the work to see if Burbridge is correct?

Light from a quasar in a galaxy, next to the nucleus, passes through 50% of that galaxy. Hence we would expect it to have absorption lines characteristic of that galaxy. Has anyone checked to see if the absorption lines are typical of light passing through 100% of that galaxy or just 50% galaxy? (100% meaning the galaxy is behind the galaxy, 50% in the middle).

Not really. This quasar, if it is 'behind' the galaxy, must be in a prime spot for gravitational lensing. Ergo if it is 'behind' the galaxy then it should be lensed with a few images. If it is 'in' the galaxy then there will be no lensing and hence no images. How many images are there of this galaxy?
Answer: none! Ergo it is in the galaxy.

5. Mar 18, 2006

### Chronos

Ergo you have a profound misunderstanding of gravitational lensing.

6. Mar 18, 2006

### SpaceTiger

Staff Emeritus
NGC 7319 would need to be both further away and more massive to produce strong gravitational lensing (i.e. multiple images) of this quasar.

7. Mar 18, 2006

### ratfink

Ah! very convenient!
I understood that single galaxies are able to produce strong gravitational lensing if one is "within a few arcseconds from the centre" - and low and behold this quasar is within a few arcseconds of the centre of NGC 7319. So why no lensing effects if the quasar is 'behind' the galaxy. Even if no multiple images, a little gravitational blurring would help to prove the case one way or another.

8. Mar 18, 2006

### SpaceTiger

Staff Emeritus
This is starting to smell trollish.

I already told you, it's not massive enough and it's too close. Gravitational lensing is much more effective when the lens is at moderate redshifts. Most galaxy lenses are ellipticals -- spirals, particularly face-on spirals, have a small or nonexistant lensing cross section.

Quasars are point sources, so they don't "blur" unless there are multiple unresolved images. Since this galaxy can't produce multiple images of the quasar, there will be no blurring.

9. Mar 18, 2006

### ratfink

appologies, it wasn't meant to be.

"much more effective", is not the same as none at all. As stated earlier, single galaxies can act as lenses if the quasar is near the centre and this quasar is near the centre. Also how 'close' is 'close?' One can have nearby lensing systems - see here. I know that this is a large cluster but it is at a redshift of z = 0.042 whilst our lensing galaxy NGC 7319 is at a redshift of 0.0225 - only half as far away as a system known to produce lensing.

So we have a quasar close to a galactic centre (a situation known to produce lensing) in a galaxy half as far away from a lensing cluster (a situation known to produce lensing) so why not a little bit of lensing in our quasar?
Even a tiny tiny bit of unresolved images would do it (how about a couple of fuzzy bulges either side?). This would show beyond doubt that the galaxy is far behind the galaxy and lensed - and not inside it. No lensing means the quasar is inside the galaxy, mainstream cosmology needs to show lensing - or is there some other way to separate the two models?

'can't' is a dangerous word to use in science and especially cosmology!

10. Mar 18, 2006

### SpaceTiger

Staff Emeritus
In the image of a point source, it is. Unless there are multiple images produced in the lensing, the point source will not be distorted. It will be magnified somewhat by weak lensing, but we wouldn't be able to tell.

Well, as you say, that's a galaxy cluster, not a galaxy. Near the center, clusters have a much higher surface density and are much more capable of lensing quasars. If the source (quasar) is very far away, then in order to produce strong gravitational lensing, one needs a surface density larger than

$$\Sigma_c=\frac{c^2}{4\pi Gd}$$

A nearby face-on spiral, unless it's extremely massive, won't be able to produce this, so it won't produce multiple-image gravitational lensing. There will be weak lensing effects in the source, but unlike with galaxy sources, a quasar point-source image won't be distorted by it.

You should probably stop putting in these little rhetorical comments. Do you really need me to explain why they're silly and illogical?

Last edited: Mar 18, 2006
11. Mar 18, 2006

### ratfink

Oh. So it is either a point source or it is multiple images? In that case there must be a minimum angular separation between these images. Below this separation we have a magnified point source, above this minimum separation we have multiple images. Just out of interest, what is this minimum angular separation of the images of a lensed quasar?

12. Mar 18, 2006

### SpaceTiger

Staff Emeritus
No, below the critical surface density, there is only one image. Given infinite resolution, this image would be distorted, but quasars are never resolved in images like this, so they continue to appear as point sources.

The whole purpose of science is determine what is and isn't possible in the natural world and then quantify the behavior. If "can't" were a bad word in science, then we would be forced to answer every question in the affirmative. I don't know where you got your impression that we can't rule out things in cosmology.

13. Mar 18, 2006

### Nereid

Staff Emeritus
quasars and galaxies; lensing, weak and strong

Detection of Cosmic Magnification with the Sloan Digital Sky Survey, by Scranton et al., is probably the most extensive study of the (weak) lensing of quasars by galaxies (and clusters).

The Introduction to this paper includes a nice summary of the 'state of the art' prior to this paper.

The CASTLES survey is one search for lensed quasars (an example of strong lensing), using the HST.

The results of these, and other work, are quite clear - quasars are at cosmological distances, and the inferred space densities match predictions of the concordance cosmological models, within a sigma or two. AFAIK, there is no alternative theory that comes close to this degree of match (between observation and prediction), except (of course) those which predict essentially the same thing - in this space - as the concordance cosmological models.

Here is the Galianni et al. paper on the NGC 7319 quasar.

ratfink, if you'd like to do some independent research on quasars (esp the NGC 7319 one), lensing of quasars, or develop an alternative to the mainstream on quasars (or cosmology), please go ahead. When you're ready, PF's IR section is available for you to submit your work, should you choose to have PF's Science Advisors critique any such work.

In the meantime, we welcome your questions and (mainstream) contributions on this topic.

14. Mar 19, 2006

### ratfink

The reason I stated that 'can't' is a dangerous word in science is that scientists who, in the past, have said something 'can't' happen have always gone on to be proved wrong by observation!

15. Mar 19, 2006

### ratfink

Sorry, my fault. I thought that this was a discussion board. I now see that it is not.
I thank you for you kind offer of a critique but, if you don't mind, I prefer to publish in peer reviewed journals. However, may I extend the same offer to yourselves at PF. Should any of you like any help or a critique of your work, just e mail me and i would be pleased to help out.
Please see my other post re posters acting as moderators.

16. Mar 19, 2006

### Nereid

Staff Emeritus
You may wish to review the Physics Forums Global Guidelines; in particular this:

17. Mar 19, 2006

### SpaceTiger

Staff Emeritus
We're looking at the observation. You said theory predicted something that contradicted the observation. I'm saying you're wrong. Now you're telling me the theory might be contradicted by the observation. It looks like you pick your cherries while spinning! Careful you don't pick any crabapples in your disoriented state.

18. Mar 20, 2006

### Chronos

I'm satisfied you are clueless.
Yes. Read the papers already mentioned, ratfink. I would be more tolerant if you asked honest questions, but, you don't. You rely upon crackpot references.

Last edited: Mar 20, 2006