Radio Galaxy Zoo Talk

There is radio but no infrared

  • jevomiguel by jevomiguel

    I understand that the radio frequencys are the jet pars, and the infrared point is the black hole, but in the bottom left corner there is a brilliant point in radio freq, but there isn´t a infrared point, there is two, what does it means? Thanks.

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

    Welcome to RGZ, jevomiguel!

    Assuming a radio source - whatever its shape (compact, elongated, or anything up to really complex) - is not an artifact (unlike optical images, such as what you see in Galaxy Zoo, here in RGZ we are classifying radio images produced not by a single mirror, but by interferometry ... artifacts are more common in images produces this way), the absence of an IR source near a bright radio source is almost always due to one of two reasons/causes:

    • the radio emission is part of a lobe or other extended structure, which may appear compact because only the hotspot is (radio) bright enough
    • the host galaxy is so faint, in both WISE IR and SDSS optical, that it doesn't appear

    For the former, you can sometimes - but by no means always! - see the counter lobe/hotspot nearby. In this case, it seems there is no such counterlobe.

    For the latter, it is usually because the host is so far away (has such a high redshift) that it's invisible, even in the IR. For me, that's the more likely explanation here.

    Hope this helps, and happy hunting! 😃

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