Infrared images...
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by Plenum
When we look at the infrared images, are we looking at a very specific portions of a galaxy, perhaps the central core where the black hole presumably exists? With the other IR sources being nearby individual/pairs/triplets, etc., of stars? And, for what appears to be very distant sources of radio emissions, is the IR source perhaps the entire galaxy? (I don't think so...) I guess a more general question is, "What are the sources of the IR wavelengths in the images we are classifying?" ((I've read the general science articles last night, but don't recall this being addressed.))
Thanks for your answers... Plenum
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by 42jkb scientist, admin
Hi Plenum, great question. The infrared emission tells us about whether or not there is star formation occurring in a galaxy. We see this in the infrared because when stars form the dust surrounding them get heated and emit in the IR. Some galaxies have no star formation and then the infrared shows us the star light, this is typically elliptical galaxies. Here is a good website that shows how galaxies look in different light, the one at the bottom, Centaurus A also has the large radio jets/lobes. http://www.aao.gov.au/local/www/alopez/multiwave.html
Let me know if I haven't made this clear.
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On the infrared images. Some questions I have:
How bright should the infrared source be? Should it be nearly white, or is a barely red dot (possibly a partially obscured by dust galaxy) also a valid source?
Can the overlapping of wavelengths be skewed and distorted by lensing? And if so, should this be taken into consideration?
Could multible IR sources be influencing a radio source? I have found in one complicated image strange contours in radio that seemed to show an effect by multiple IR sources which I thought might be gravitational pull on the radio source by nearby IR sources.Sorry if I ask stupid questions, I havn't studied astrophysics for many years, and not up to speed with current theories.
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by ivywong scientist, admin
Some of the radio jets are nearby so their IR galaxy counterparts should be bright. But if the jets look small and there is a faint galaxy that can be associated to it, then it's probably a very distant galaxy and it's ok to associate this with the jet.
To my knowledge, there aren't many radio lenses so I would say that we wouldn't see many (if any) of them.Sometimes groups of galaxies may each have their own jets but it will be difficult for us to tell them apart so it might get grouped into one big strange looking jet/plume and if we think that there are multiple candidates that can be responsible for them, we can select all the relevant IR sources 😃
Ps/ As I mentioned before, there are no stupid questions! Only silly answers 😉
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by Qoiorav
Thanks for the explanations, I was wondering myself what exactly the source of the infrared emissions was, and how I should deal with less intense infrared sources and skewed or barely overlapping emissions. If Zooniverse would explain this in greater detail more accurate classifications would surely follow!
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by ivywong scientist, admin
@Qoiorav: Judging which IR source is relevant is very difficult for non-overlapping radio+IR emission. The source of the IR emission comes from the stars within the galaxies. This is why some IR images appear saturated if they contain a Milky Way star in the field of view. If the less intense IR sources are in the "right position" (eg. right in between a double-lobed radio source), then it's likely to be the correct match. Unfortunately there are many fields where the classifications aren't as easy and will require follow-up investigations to determine the proper matches with good accuracy.
Hope this helps 😃
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by Rimbaud
I don't see a clear answer to following two questions:
How bright does the IR source have to be for us to identify as a "match"? Some are very faint. Do you want it included anyway as a match?
How overlapping do the IR sources have to be or do you want them identified as a match even if only overlap slightly or merely seem to touch?
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by JeanTate in response to Rimbaud's comment.
@Rimbaud: I just answered a similar pair of questions, posted by you, here.
How bright does the IR source have to be for us to identify as a "match"? Some are very faint. Do you want it included anyway as a match?
I mark as associated an IR source ones that can be very faint. From the POV of this project, my feeling is that it's better to have false positives (i.e. identified IR sources which are not real) than false negatives (i.e. not marking a faint IR source, which turns out to be real).
How overlapping do the IR sources have to be or do you want them identified as a match even if only overlap slightly or merely seem to touch?
For compact (or somewhat extended) sources, I think the center of the radio emission should be within the "IR footprint" of an IR source. Sometimes I think there's an association even though there's only the slightest bit of an overlap; I mark these as #offset.
For #corejets, one end needs to be within the IR footprint, I think. Similarly for #corelobes (which are, very likely, triples, but one lobe is too faint to register).
For #hourglasses, the IR source should be ~in the middle of the radio emission.
I think it's up to your own judgement for #doublelobes (and #wats and #nats, and ...).
Hope this helps, and happy hunting! 😃
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by mattdanley33
What if a small galaxy plunges directly through the center of a larger disk-shaped galaxy, can a collisional ring galaxy can result? The unusual systems can look like smoke rings in lacking a central nucleus, however, a ring in this case represents a shock wave moving outward,
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by ivywong scientist, admin
Yes, this is possible. As a matter of fact, I just had a paper accepted for publication on a study I did on a collisional ring galaxy: https://arxiver.wordpress.com/2016/11/29/early-science-with-the-large-millimeter-telescope-discovery-of-the-12co1-0-emission-line-in-the-ring-galaxy-viizw466-ga/
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by Plenum
...and five years' worth of comments over that time have been great! Thanks for all responses!
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by ivywong scientist, admin
You're very welcome and we're very happy to see you on RadioTalk 5 years later as well.
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