Radio Galaxy Zoo Talk

no SDSS object

  • nico775 by nico775 translator

    On the SDSS image image, there is no corresponding object. Is this object too far to be seen ? or is there no visible light associated with that object ?

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  • JeanTate by JeanTate in response to nico775's comment.

    This is a very nice #triple.

    The core/host - the galaxy/AGN that is the likely source of the two radio lobes - is SDSS J130343.10+205532.6, which is - photometrically - a STAR. Fortunately, there's a spectrum, and that shows this is an unambiguous quasar, at z=1.050

    Optical field, centered on the quasar:

    enter image description here

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  • nico775 by nico775 translator

    thanks again. I was thinking SDSS image were automatically centered on the RZG image.

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  • JeanTate by JeanTate in response to nico775's comment.

    You're very welcome.

    I was thinking SDSS image were automatically centered on the RZG image.

    To within a pixel or two (or perhaps an arcsec or two), all the links below an RGZ image - FIRST, NVSS, SDSS, WISE - will bring up cutouts/images that are centered at the same location as the RGZ image. Or not: at the right below the image is a coordinate location, an RA and a Dec pair of numbers. These are now quoted to three significant places; it may be that at least one of five linked images is centered on this (not that the difference is noticeable, except in SDSS).

    If - as in this case and many others - the core/host (the galaxy containing the AGN etc which is the source of the jets/lobes/etc) is not at (or near) the centroid of the radio source in the center of the RGZ image, then you'll have to work to find the likely core/host.

    Here's what I often do, especially when the likely core is quite some way from the center:

    • open both SDSS and WISE
    • in SDSS, check the 'Objects with spectra' and 'Label' boxes, and click on the bar one to the left, in the zoom tool
    • (this makes the SDSS Navigate image approx the same size as the RGZ one, as confirmed by the scale in the label)
    • often that's enough to be able to pick out the likely optical counterpart to the IR source that's the core; moving the cursor to click on that object and then clicking Explore (right panel) brings up all there is to know about that object, in SDSS
    • sometimes I need to get the location more exactly: in the WISE Band 1 image, move the cursor so that it's over the centroid of the IR source (may need to switch back and forth with the RGZ image to be sure)
    • read the (RA, Dec) location from the panel at the top right (choose the second Eq-J2000; I just remember the first three decimals of each coordinate)
    • go back to SDSS Navigate, more the cursor so that it's close to WISE location; if there's something there, click Explore

    Of course, if there's nothing in the RGZ IR image, it's much harder; however, in these cases it's highly unlikely you'll find anything in SDSS anyway ...

    Hope this helps.

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  • nico775 by nico775 translator

    helping a lot...

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