Radio Galaxy Zoo Talk

ARG0002j9g GALAXY SDSS J112701.71+170744.7 with large IR & very small RADIO contour

  • A1001 by A1001

    what is the cause of the large IR & very small RADIO contour/
    SDSS J112701.71+170744.7

    enter image description here

    SDSS J112700.90+170711.3

    enter image description here

    Posted

  • JeanTate by JeanTate in response to A1001's comment.

    The fundamental answer is that the physical processes which produce the IR we see in WISE images and the radio in FIRST ones are very different. And related only indirectly.

    For example, infrared is (strongly) produced by stars (more or less as blackbody radiation) and dust (ditto, but dust is more efficient, being a lot cooler than stars). And by AGN (active galactic nuclei), where several different physical processes are at work (holler if you'd like some details).

    Radio - of the frequency we see in FIRST images - is primarily produced by a synchrotron process, fast electrons spiraling in magnetic fields (perhaps a radio astronomer might jump in here to add more?). Where do you find lots of hot electrons and non-zero magnetic fields? In supernova remnants (which is why you see FIRST radio sources marking the sites of star-formation; star-formation means massive stars, which go boom!), and in AGN.

    In some galaxies with AGN, there is a nuclear star-burst (lots of stars formed "recently", lots went supernova); and also lots of dust (similar reasons). In all AGNs there is a lot of hot plasma, and magnetic fields. So AGNs are often - but not always! why not? - FIRST sources.

    Some AGNs, by processes not yet well-understood, launch back-to-back jets of highly relativistic particles; think the LHC 'straightened out', a trillion (or much more) times more powerful. In AGNs in elliptical galaxies, these jets blast out into the intergalactic medium (IGM), eventually being stopped (weird isn't it; the IGM is a 'harder' vacuum that we could ever possibly hope to create in any earthly lab, yet it can stop a particle beam which would make the Death Star's look like a firefly). Thus we see the lobes (etc) in FIRST. Nothing in WISE there, because there are no stars and no dust.

    Of course, this is a quick summary; whole books have been written on the details (and the kinds of processes and sources I've not mentioned).

    Radio astronomy sure is fun, isn't it?

    Hope this helps, and happy hunting! 😃

    Posted

  • 42jkb by 42jkb scientist, admin

    Hi A1001,

    This is a great question!

    Yes, the infrared emission as JeanTate says come from stars and dust. The radio emission in this case comes from synchrotron radiation at 1.4 GHz (21cm). The radiation comes from relativistic electrons accelerating around magnetic fields. The acceleration produces the radiation that we detect.

    In this particular case, I would say that the supermassive black hole at the centre of the galaxy is accreting material. This accretion produces bi-polar jets that get launched. The launching process is not understood too well. The jets then pass through the galaxy and can travel to large distances from the host galaxy. The largest distances are known as Giant Radio Galaxies.

    The reason why the radio emission looks so small is that:
    (1) the radio jets are launched towards us so we don't see the extended radio lobe structure: or
    (2) the radio jets are "stuck" within the galaxy.

    Please, send more questions our way.

    Posted