Space Warps Talk

Edge on spiral Marked as #lens ?

  • JasonJason by JasonJason

    ASW0001fx6



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  • AlexandredOr by AlexandredOr

    Isn't it a spiral ?

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  • JasonJason by JasonJason

    Probably edge on, to blurred and far to tell, but just 1 of 6 that have it in a collection, so others think it is a lens also, what do you think?

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  • AlexandredOr by AlexandredOr

    I think it's not a lens..

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  • JasonJason by JasonJason

    That's ok, I do after viewing over 21000 images I think it is.

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  • Tom_Collett by Tom_Collett scientist

    To be honest, I think it's a spiral but I'm not very certain.

    Hopefully this object will pop up in one of the other images with slightly better image quality.

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  • JasonJason by JasonJason

    Do you mean spirals can't be lenses?

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  • ElisabethB by ElisabethB moderator in response to JasonJason's comment.

    Spirals are usually not massive enough to do any lensing

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  • JasonJason by JasonJason

    I found these can you explain them and what they infer

    Inclination Effects in Spiral Galaxy Gravitational Lensing http://iopscience.iop.org/0004-637X/486/2/681/fulltext/

    Gravitational lensing of quasars by edge-on spiral galaxies http://dspace.mit.edu/handle/1721.1/42167

    Gravitational Lensing by Spiral Galaxies http://iopscience.iop.org/0004-637X/495/1/157/fulltext/36599.text.html

    Gravitational lensing by spiral galaxies http://www.ias.ac.in/pramana/dec1999/c1.pdf

    Even the sun can lens as per Eddingtons experiment during the eclipse in 1919, any massive object can lens.

    The Sun as a Gravitational Lens :
    A Target for Space Missions A Target for Space Missions
    Reaching 550 AU to 1000 AU
    http://www.spaceroutes.com/astrocon/AstroconVTalks/Maccone-AstroconV.pdf

    Using The Sun as a Magnifying Glass
    JAN 10, 2011 03:14 PM ET // BY RAY VILLARD

    http://news.discovery.com/space/using-the-sun-as-a-magnifying-glass.htm

    THE SUN AS A GRAVITATIONAL LENS:
    PROPOSED SPACE MISSIONS
    Presented by:
    Dr. Claudio Maccone
    Member of the International Academy of Astronautics

    http://websupport1.citytech.cuny.edu/Dept/Physics/docs/seminars/maccone_sp08.pdf

    Surely a spiral must be massive enough, wouldn't you agree?

    There are even simulations of spirals being lenses such as ASW00013o6

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  • ElisabethB by ElisabethB moderator

    Sorry, I should have been clearer. What I meant was that spirals are not massive eough to produce lneses that we can see in these images.
    The sims around lenses are not realistic. We've been tagging them with #simfail

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  • JasonJason by JasonJason

    I still don't understand, could you explain please? How could the person setting up the simulations not know that ahead of time and not leave them out?

    I also just found this

    A search for edge-on galaxy lenses in the CFHT Legacy Survey ⋆

    J.F. Sygnet1,2
    , H. Tu3,1,2
    , B. Fort1,2
    , and R. Gavazzi1,2

    http://hal.archives-ouvertes.fr/docs/00/47/43/31/PDF/3977sygnet-for-AstroPH.pdf

    page 6 shows 16 candidates from the survey which appears to differ from what you state ie. the survey and camera is capable?

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  • Tom_Collett by Tom_Collett scientist in response to JasonJason's comment.

    The key phrase in your examples is 'edge on.'

    Spirals aren't very massive, but they are very flat. Lensing is sensitive to the projected mass of the galaxy rather than the total mass (this is pretty academic for ellipticals but not for spirals). If the spiral is edge on, the projected mass is much larger than the same galaxy seen face on (The mass hasn't changed, but the area of the sky filled by the galaxy has). The galaxy here is somewhere in between the two cases, but they really need to be almost perfectly edge on to have a significant chance of lensing.
    See how all the candidates in the Sygnet paper are edge on?

    The simulations are made by a robot rather than a real person. There are way too many simulations to do it by hand. The robot picks what it thinks is a plausible lens galaxy, generates a mock mass model consistent with the lens light and uses this to lens a plausible background source. Where the simulations show a face on spiral, it's because the robot has failed (#simfail) - it sometimes thinks that the center of the spiral is an elliptical, so simulates a lens. By eye we can tell they are face on spirals (and hence almost no chance of being a lens), but the robot can't. Everytime you see a face on spiral as a simulated lens, please mark it as a #simfail - this will help improve the robot for future iterations of spacewarps.

    BTW viewed from earth the sun can't act as a STRONG gravitational lens - it isn't massive enough for us to see multiple images either side of the sun, but it does deflect starlight passing close to its surface by about 2 arcseconds (the sun is about 1000 times larger than this). It may be possible to use it as a gravitational lens from the outer solar system - but I don't think this will ever be a plausible space mission.

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  • JasonJason by JasonJason

    Thanks again Tom for another enlightening explanation

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  • JasonJason by JasonJason

    So all we are really looking for are quasars, elliptical, strict edge on spirals and groups of galaxies that act as a lens?

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  • Budgieye by Budgieye moderator

    Yes to elliptical, edge-ones, and groups.

    A quasar is not necessarily a good lens, any more than an dormant black hole in an elliptical. and it might have many colours around the nucleus which can confuse the image. The quasars we look at are background quasars, behind the lensing galaxy.

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  • Stedman by Stedman

    Aah! Having read this I suspect I've marked some as lenses that are really just spirals. Thanks for the clarification.

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  • drphilmarshall by drphilmarshall scientist, admin

    Great comment from Tom. I'd only add one thing:

    It is possible for face on spirals to act as lenses, their yellow bulges are fairly massive (and dense). However, a spiral galaxy bulge is like a low mass elliptical galaxy: its Einstein radius will be small. The reason the #simfail systems are not convincing is because the arcs are too far out to be plausible! If you see arcs around a spiral galaxy bulge, they'll be more plausible as lensed features if they lie very close to the bulge itself (like the #buriedrings).

    Many of the systems identified by Sygnet et al are examples of weak lensing, where a background galaxy appears a bit distorted and magnified, but not multiply-imaged. It's the multiple-imaging we need to make accurate mass measurements. For some really nice edge-on disk lenses, check out papers by Dutton, Treu, Brewer et al in the SWELLS collaboration - but watch out, the HST images in those papers are significantly higher resolution than the CFHT images in Space Warps right now! Remember: for galaxy scale lenses, we're looking for buried treasure.

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