Radio Galaxy Zoo Talk

ARG0001gar - quite strong radio source, wimpy z~0.6 optical; common?

  • JeanTate by JeanTate

    First, is this more likely a double lobe or a core jet? Or something else?? And how do you tell, given that you can't say just where the optical source (SDSS J164932.69+344251.0) is, with respect to the midpoint between the local radio peaks?

    The candidate host is really wimpy:

    enter image description here

    Or not.

    If it is indeed at z~0.6, it's likely a 'giant elliptical'. Yet, here in RGZ, we've seen QSOs with fewer radio contours, out to at least z~1, even z~2, and they're optically quite (SDSS) bright stars.

    To an OOM (order of magnitude) or two, how common (or not) are bright extended radio sources/faint z~0.5-0.8 optical sources?

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  • JeanTate by JeanTate

    ARG00003kl contains another example (bottom right/SW)1: pretty strong radio source, but very wimpy optical (z_ph ~0.675 SDSS J114952.01+610751.0):

    enter image description here

    1 It's not as extended as ARG0001gar, but it's also clearly not a point source.

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  • WizardHowl by WizardHowl

    From my own experience I would say that these kinds of sources (I think of them as doublelobes or hourglass sources) are more common than ifrs sources, by a factor of at least two, maybe three or more, depending on where you draw the line at 'strong' radio source. In some cases there might be two independent radio sources on a line-of-sight although these should be less common, given that both host galaxies would have to be faint in optical. The really strong ones are rarer but I suspect identifying what is behind them will have to wait for next-gen surveys.

    Here's a bright example of a doublelobe that has no exact optical match (a nearby faint object is offset a bit too far to be likely from overlaying the images in SkyView), and extremely weak in IR: http://radiotalk.galaxyzoo.org/#/subjects/ARG00035mr

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  • DocR by DocR scientist

    I think these are just faint, distant double lobe radio galaxies. The statistics are kind of tricky because the reporting by individuals is based on what they find interesting. We'll have a much better handle as the pipeline processing develops.

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  • JeanTate by JeanTate

    Thanks WizardHowl, DocR.

    Having come across at least two, I conclude they cannot be rare, and agree that they're likely to be at least as common as 'single source' ifrs (within a factor of ~3+).

    is this more likely a double lobe or a core jet? Or something else?? And how do you tell, given that you can't say just where the optical source (SDSS J164932.69+344251.0) is, with respect to the midpoint between the local radio peaks?

    My tentative answer is that you can't tell. In most cases, the radio morphology is at best ambiguous, and given radio/IR-optical (mis)alignment (both accuracy and precision), any IR/optical counterparts could be potential hosts at one radio peak (making it a core-jet/single-lobe) or ~midway between them (making it a doublelobe/hourglass).

    With lots of examples, and robust classifications, I guess it will be possible to start to try to untangle projection/inclination effects, and see if there are any patterns in observed radio vs IRoptical flux.

    Somewhat related: I wonder what makes for a radio-bright core (not a lobe) but an IR/optically faint one? If such an object is also x-ray bright, I guess the answer (or part of the answer) is "dust" ... which suggests such objects would be very bright in the mid- to far-IR.

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