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Originally Posted by parejkoj
First off, thanks for the reply. I'll try and provide a brief (or maybe not so brief... sorry) lesson in eyeball spectroscopy as part of my reply. To really understand these sources, you have to do a deeper analysis of the spectrum, fitting the various lines and the continuum. But you can make some obvious comparisons between sources much more simply.
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Thanks for the lesson. I ensure you that it's appreciated.
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Originally Posted by parejkoj
Also, a technical question about the board itself: when I click the "quote" button, it only quotes your reply, not my comments that you are replying to. Is there a way to get it to quote the entire conversation, so I don't have to go back and fill it in?
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I don't think there's a way around that, other than constructing the quotes yourself.
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Originally Posted by parejkoj
Hmm... Unfortunately, the STSci archive is down, so I can't access the archival HST data for that region, and it's out of the SDSS coverage area. But glancing at their radio map, the radio source that they are assigning to the galaxy *could* just be a jet from the quasar. I can't say much without knowing more about the objects. According to the data from Lehnert et al. 1999, the redshift of 3c343 is actually 0.998, and they call it a Seyfert 2 galaxy. Though, that's a fine splitting of hairs, if you ask me. |
Sorry, I was little sloppy there. I looked at NED and noticed they give same redshift you are citing, but they refer to a paper from 1985. So then I got to thinking that perhaps there's a mistake in the abstract of the paper I cited, because that's where I copied the numbers. I opened the abstract page of that paper again and then it hit me, they are talking about 3C 343
.1 not 3C 343. A small but significant difference, sorry about that. (NED only gives one redshift, the 0.75, for 3C 343.1.)
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Originally Posted by parejkoj
By luminosity profiling, do you mean determining the light profile of the source?
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Yes.
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Originally Posted by parejkoj
But I don't think the DSS PSF is well enough determined to do PSF subtraction
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Just so that it is clear: without PSF subtraction, the luminosity profile of the point-like source is useless?
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Originally Posted by parejkoj
well, photometric redshifts are getting pretty accurate these days, but they are based off of an understanding of the spectral properties of the sources
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From what I've seen in SkyServer, they are still quite far from truth. I think currently I wouldn't trust studies using photometric redshifts to be more than preliminary results, I think they should be confirmed with real redshifts. (Incidentally, the Scranton et al. study mentioned in this thread uses photometric redshifts...)
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Originally Posted by parejkoj
But remember, if the spectral classification is wrong, the redshift could be as well!
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This feels little strange to me. If there's many spectral lines in object's spectrum, isn't the redshift determination then quite solid (excluding some anomalous cases)? I mean it would be quite a coincidence to have all lines showing the same wrong redshift, wouldn't it?
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Originally Posted by parejkoj
Good guess; this confused the heck out of me when I first saw it.
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You're not the only one, NED has two entries for it,
one as a galaxy, and
one as a QSO (with BLLAC as description). (BL LACs are something Arp considers to be a later stage to quasars in quasar to galaxy evolution cycle.)
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Originally Posted by parejkoj
BL Lacs are currently thought to be systems where we are looking directly into the "mouth of the beast," if you will. Direct line of sight into the central black hole with the relativistic jet pointed at us. There are less than a thousand known BL Lacs: a hundred or so with SDSS spectroscopy. So, according to the standard view, this is very similar to a quasar, but viewed at a particular angle. It has many of the same properties of other quasars: bright in X-ray and radio, high variability, and a bright point source in the core of a galaxy.
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So the redshift of BL LACs don't tell the distance to the objects, because there is quite substantial blueshift due to the velocity of the material in the jet towards us? (I tried to peek at the redshift distribution of BL LACs but apparently you can't query just for BL LACs in NED.)
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Originally Posted by parejkoj
Oh, good... I was just chiding myself for not including one of the quasar-like stars on my list, but you found one for me! In the Finding Chart and Navigation pages (I prefer the Navigation, as you can go directly from it to the Explore page for a selected object), you can click the "objects with spectra" box on the left to get red boxes around sources with SDSS spectroscopy. One of your three quasar candidates is actually a blue star. Possibly a white dwarf, though I'm no star expert (if any are reading this, please clarify!):
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And in "PrimTarget" it says "TARGET_QSO_CAP"...
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Originally Posted by parejkoj
I'll deal with these two together, as they are interacting companions (check the finding chart if you don't believe me; the redshifts are the same).
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As I'm willing to give Arp a benefit of doubt, I don't even need the redshifts to be the same to believe that two objects are interacting. However, due to that same reason, I also don't believe that two objects are interacting just because their redshift are the same.
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Originally Posted by parejkoj
The first is a galaxy hosting a quasar (notice the broad emission lines and spectrum that gets stronger towards blue?)
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Well, so far all objects seem to have spectrum that gets stronger towards blue, especially the one you called possibly a white dwarf. So, I guess that feature doesn't distinguish between quasars and stars then?
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Originally Posted by parejkoj
Compare the two spectra with (1): notice how similar the first is, while the second looks very different.
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That probably requires some experience, because besides the fall off I don't notice much difference in lines, sure there's some difference like the couple very narrow lines in galaxy's spectrum, but the galaxy has also a quite broad line at 7000 Å. I don't think I could distinguish these two from each other (in the sense that are they a quasar or a galaxy) without the fall off.
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Originally Posted by parejkoj
There is a spiral galaxy there, but compare the spectrum with the two above; which does it look more like, the star-forming galaxy, or the quasar? Also, compare it with (1). If you use Firefox, Opera, Safari, or another browser with tabs, open each spectrum in a separate tab and flip between them quickly: (1) looks like a redshifted version of this one.
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Yes, but this one doesn't have stronger spectrum towards blue.
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Originally Posted by parejkoj
It is a double star system, but the resolution of SDSS is not quite good enough to separate them. The spectrum looks odd, but that's because we are seeing the spectra of both stars (one cool and red, the other hot and blue) overlaid on top of each other.
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I can see that. Is this kind of spectrum happening only in double objects, or are there objects that produce similar spectrum by themselves?
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Originally Posted by parejkoj
Good call! I'd actually say this is more likely to be a planetary nebula in the blue, star-forming galaxy, rather like the owl nebula (M27) in our own galaxy. Compare it with this spectrum that was taken of a knot in the owl. Strong [OII], very weak H-alpha and H-beta, generally flat continuum. Also compare it to the not-quasar star-forming galaxy in interacting pair above. |
Curiously, it says "z = 0.0052 +/- 0.0012 (0.40), QSO" in the image of the spectrum. I wonder if that's an automatically created text, or did someone write it there?
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Originally Posted by parejkoj
The redshift is high: greater than 2, and it has a strange, very blue spectrum. None of the lines of the other objects above would even be in the SDSS spectral band anymore, due to the high redshift! The strange spectral shape may be due to iron emission (not fit by the SDSS spectroscopic pipeline), or very hot gas (at that redshift, the "peak" around 500 nm corresponds to ~150 nm, which is far-UV!). I might call it a quasar, but that's because the spectrum doesn't look anything like a typical star or galaxy.
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I'm not sure I understand why. This object has couple of quite narrow looking emission lines, and a fall off toward blue.
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Originally Posted by parejkoj
Don't assume that anyone else can identify a quasar just by looking at it!
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I don't, I just meant that Arp probably can do it as well as anyone else, I didn't mean I think he (or anyone else) can do it perfectly.
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Originally Posted by parejkoj
Personally? I don't really know if Arp has an actual working definition of the term quasar, beyond what you said above about looking like a star but having high redshift. From what I've seen of Arp's work, his quasars are simply those objects that he has selected from other catalogs (SDSS, 2df, or even NED) for his own analysis, thus they are whatever the given catalog classified as a quasar.
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I don't remember seeing Arp address specifically his definition of quasar, but I think that browse through some of his papers would reveal at least some details more. I might check for some later if I have time.
For other parts of your post I didn't respond: thanks for the info!