Galaxy Zoo Talk

Lensing

  • colcol by colcol

    Does this show gravitational lensing?

    Posted

  • Capella05 by Capella05 moderator

    I think it is meant to simulate it 😃

    Hopefully one of the Illustris project scientists could confirm if this is the case!

    I will flag it up!

    Posted

  • KWillett by KWillett scientist, admin, translator

    Great question, and good spotting from the Zooites who tagged this as an arc! I do agree that it strongly resembles the examples of strong gravitational lensing that have been already found in Galaxy Zoo images (and done in more detail at SpaceWarps). This particular case isn't a lens, however (confirmed by the Illustris scientists).

    The nature of the simulated images actually makes it impossible for gravitational lenses to appear in these images. The main reason is due to computational limits; in the real Universe, a gravitational lens is what you see when light from a very distant galaxy is warped by the gravitational effects of an intervening galaxy or cluster. To trace that in a simulation, the program would need to trace the simulated photons from every galaxy in every direction over an enormous volume. It's simply not possible to do that at every step; these images are made by considering only the stars/gas/dark matter particles from the local environment (known as the "subhalo") and then rendering that as the images you see here. The backgrounds that you see are randomly generated from SDSS imaging, and so the galaxy in the center really doesn't "know" about any other galaxies either behind or in front of it. Hence, lensing isn't possible to observer.

    So - the blue arc that you've spotted is likely a low-mass satellite galaxy in the simulation that has just made a close passage to the large galaxy in the center. That triggered star formation in the satellite due to tidal disruption, which results in the blue color and the long stretched appearance.

    If you see features like this in future images, definitely classify them as "lens or arc" in the interface, since we do want to know how well this correlates with merging events. Feel free to use the #arc or #illustris_arc hashtags on Talk as well.

    • Kyle

    Posted

  • Capella05 by Capella05 moderator

    Thank you Kyle!

    From a personal point of view - I am disappointed that we cant see simulated lenses in the Ilustruis images. Lenses are a favourite of mine.

    As for "low mass satellite galaxy" Hmmmmmm.

    But, I will still keep on clasifying 😃

    Posted

  • KWillett by KWillett scientist, admin, translator

    It would be neat to see, and there are lots of simulations that do do lensing. The problem is simply that it's mind-bogglingly expensive (in terms of computing power) to do it for all galaxies on this scale. You'd also have to add general relativity to your ray-tracing calculations, which I'm pretty sure Illustris doesn't do.

    Posted