Galaxy Zoo Talk

arcs, lensing and overlaps : can we get some cool examples of each?

  • wouterretuow by wouterretuow

    I often get a small feature next to a big one, giving the impression that it's too close to be just accidental. So I would like to know the telltale signs for calling something a (potential) arc or lensing. Lest I spew out false alarms all the time.


  • Ghost_Sheep_SWR by Ghost_Sheep_SWR in response to wouterretuow's comment.

    You can get more info and examples here:

    3.9 Gravitational lenses

    They usually have a very different color from the lensing galaxy, have distinctive shapes and are very rare.

    Given all the human and algorithm searches that have been done and are ongoing (in SDSS and deeper surveys), and given how rare they are I think the chance of finding an unknown one is near impossible.

    Most small things near galaxies are usually tidal debris, a dwarf satellite galaxy, overlap of a more distant galaxy etc.


  • jeffreyhrwtz by jeffreyhrwtz

    What about these very faint objects in the Gama survey? Will the genuine arcs definately be another color?


  • Ghost_Sheep_SWR by Ghost_Sheep_SWR in response to jeffreyhrwtz's comment.

    AFAIK the current GZ GAMA KiDS dataset is two-coloured based on two bands which severely limits the colour range to distinquish unique objects.

    So it's probably possible a lensing and lensed galaxy have clear different 'colours' there's no way to tell by colour if it is a lens or something else. Ofcourse gravitational lenses have very distinctive shapes too, and I'm sure a lens shape will be obvious in GZ GAMA images.

    Since GAMA images are much deeper than say SDSS this might lead to finding new g-lenses, but it wouldn't surprise me if the data has already been thoroughly run through by arc / lens finding algorithms.


  • Ghost_Sheep_SWR by Ghost_Sheep_SWR

    Found one of them, as you can read here fewer monkeys are needed;