Curious lens/lensalike object
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by mrpsb
Hiya,
Just come across this image, the group of galaxies at the top looks like it has a couple of arcs although they're not massively curved and the top one looks like it curves one way and then the other. Any thoughts?
Thanks
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by ElisabethB moderator
I agree, it looks weird, but I'd definitely flag this one !
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by mrpsb
Yep, marked it up and tagged it 😃
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by Capella05 moderator in response to mrpsb's comment.
Nice Find 😃
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by mrpsb
Appears to be same object as the one in ASW00022of which is easier to seethe whole thing in!
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by Capella05 moderator
Just remember - you still spotted it 😄
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by Tom_Collett scientist
It's definitely a lens. The complicated mass distribution of the group gives the weird configuration to the blue arcs, compared to the training images which are mostly made using a simpler mass distribution. (But you will see some more complicated ones too)
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by AlexandredOr
Great lensing !!
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by JasonJason
That is already a known one it can be found in here page 8 # 22 021409−053532 and here as
#22 http://kicp.uchicago.edu/~anupreeta/sarcs_sampleSorry it is a known one but good eye!
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by Tom_Collett scientist
It doesn't matter that it's already known - it's important to prove that spacewarps can find real lenses!
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by Capella05 moderator in response to Tom Collett's comment.
Agreed.
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by JasonJason
I know that, was just pointing out that it was a known one? It is expected that all 127 will or should be spotted.
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by Tom_Collett scientist
Yeah I think we'll get all 127 and a fair few more (Like this one, the known group scale lenses stick out like a sore thumb - the unknown lenses will be the harder ones to find)
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by JasonJason
Do you think the unknowns will have a high degree of similarity or more variability than the current known ones, and there are some of the known ones that are in question right?
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by mrpsb
Glad I finally spotted a definite one, even if it is because it's already known 😄
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by JasonJason
Like a said, good eye, keep up the good spotting!
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by Tom_Collett scientist in response to JasonJason's comment.
Good questions. Yes some of the known ones may not be lenses - you can never be sure until you have a redshift for both lens and source, but the best test is to fit a lens model to them - if you can get a plausible lens model, with the lensing mass well aligned with and very close to the visible galaxy, then the chances of lensing are pretty high. If you can't get a good model, then it's very unlikely to be a lens. The SARCS website (http://kicp.uchicago.edu/~anupreeta/sarcs_sample) has a quality flag for the known systems - this one is 4.0 or "definitely yes" - the scale goes from 1 to 4 (I think the zeroes haven't been modeled yet - modelling group scale lenses takes ages to do properly)
What will the unknown lenses look like? I don't know - they are unknown! I suspect they'll look slightly different, or the robot would have found them. I suspect they will be in crowded fields, or near bright objects that might have confused the robot. Fainter arcs and smaller image separation systems may also sometimes escape the robot. All that being said, it's an informed guess at best.
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by drphilmarshall scientist, admin
Verdugo et al studied this lens in some detail, you might like to read their paper: http://arxiv.org/abs/1005.1566
Nice example of the kind of modelling we can do with the lenses you find, after they are followed-up. Weighing groups of galaxies, figuring out where the dark matter is 😃Posted