Radio Galaxy Zoo Talk

If ifrs means 'infrared radio source', then ...

  • JeanTate by JeanTate

    ... how come that hashtag can be applied to a radio source where there appears to be no IR counterpart?

    At best, all you can say is that such an object is an ifrs candidate, surely?

    Aren't there many - known - kinds of 'radio source without infrared counterpart' which are not high redshift (galaxies with) AGNs? For example, pulsars, RRATsWP, ...

    Besides, if you find a compact radio source and at the same location a compact IR source, isn't that - by definition - an 'infrared radio source'?

    In short, isn't ifrs a close-to-useless hashtag (or at least a highly confusing one)?

    Posted

  • enno.middelberg by enno.middelberg scientist, translator

    Most "normal" galaxies follow the radio-infrared relation, which is an observational fact that radio emission and infrared emission pretty much scale with one another. The brighter the radio, the brighter the IR.

    IFRS are special because it is quite difficult to understand how objects can produce so much radio emission without IR. If they are extended we understand what's going on - large radio lobes don't come with much IR emission, but more compact objects are difficult to understand. It seems they are at rather high redshifts (z>2...3), and fainter IFRS may even be located at even higher redshifts.

    When IFRS were discovered/identified (see http://arxiv.org/abs/astro-ph/0610538 for the discovery paper) it was clear there were many potential explanations, but we have ruled them out one by one. For example, the number of IFRS is much higher than the number of pulsars, so while the one or other IFRS could be a pulsar, most are not (see http://arxiv.org/abs/1103.6062).

    The general definition of IFRS is that the radio is more than 500x brighter than the IR, so without knowing the flux densities of the sources every IFRS is speculative. And if the radio-to-IR ratio is only 100, but the source is faint and the IR happens to be below the sensitivity of the IR telescope, than we have, as you say, a IFRS candidate.

    But when the radio is bright and the source is compact (which means it is the size of a galaxy, and doesn't have jets and lobes) and there is absolutely no IR emission then I'd like to keep the #ifrs tag, because these buggers are really, really puzzling. See also my other post on this at http://radiotalk.galaxyzoo.org/#/boards/BRG0000002/discussions/DRG00000ld.

    Posted

  • mini.mintaka by mini.mintaka scientist

    Awesome response enno.middelberg, but I think JeanTate just thought IFRS was 'Infrared Radio Source' when in fact IFRS stands for 'Infrared FAINT radio source' 😃

    So Jean, IFRS is used when there is a radio source without a clear IR counterpart. The reasons for this are outlined by Enno above.

    Furthermore, IFRS differ from the 'relic' classification as relics tend to be more diffuse. I hope this helped 😃

    Posted