Space Warps Talk

Can someone clear this up?

  • JasonJason by JasonJason

    This is somewhat of a continuance to the discussion on left, read that to get the background.

    The objects in this image are supposed to be Galaxies, yet when they are modeled with the SpaghettiLens modeller they both have clearly different outcomes. What is the reason for the difference in model results? Also if the galaxy on the right were further away it would be harder to determine that it was a galaxy and would need to be modeled to determine what it was, by this hypothesis it would model as it is modeled right now, or would there be a difference in modeling results if it were further away?

    So if there would be no difference in the modeling what would we assume from the model results, given an increased distance or i.e. supposed smaller images, if all we had to go on was the results??

    Image ASW0004ey1 is simmilar the galaxy on the right is much harder to make out the spiral arms and the model of the object on the left has a smooth mass distribution and clearly defined arrival time contour and circular synthetic image, and the same with the object on the right in this image. So galaxies can be modeled and have clean model results, as result of right galaxy http://mite.physik.uzh.ch/data/001886 .

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  • psaha by psaha scientist

    Lens modelling assumes that each object is really two galaxies at completely different distances: a roundish yellow-white galaxy "the lens", and a small blue galaxy "the source" far behind it. [These two objects look like nice spirals, so I'd say the assumption is not true -- but let's follow the hypothesis.] SpaghettiLens assumes by default that the lens is at redshift 0.5 and the source is at redshift 1. These numbers make no qualitative difference, though the affect the mass inferred. But there's always an assumption that the source is much further away than the lens.

    The results in 001880 and 001881 suggest that an Einstein ring could look somewhat similar to one system but not the other. The difference comes from (small) differences in the placement of the points. With SpaghettiLens if you try a sequence of models with slight displacements of the points, the results may change hardly at all -- and then suddenly change a lot. These are a transition between SpaghettiLens finding a nice smooth mass distribution, and resorting to one of the weird checkerboard mass maps.

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  • JasonJason by JasonJason

    Thank you @psaha

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  • Capella05 by Capella05 moderator

    But in the end - It is still two spiral galaxies 😃

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