Radio Galaxy Zoo Talk

Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array

  • KWillett by KWillett scientist, admin, translator

    A new paper (Hurley-Walker et al. 2014; accepted to MNRAS) appeared on the arXiv a few days ago. It reveals the discovery of a new "dying" giant radio galaxy in NGC 1534.

    What I think is interesting:

    • another example of what we think are rare objects (although we're discovering more and more of them as better instrumentation and data reduction becomes available)
    • examples of what we can see at different radio wavelengths. This is a low-frequency discovery using the Murchison Widefield Array in Australia. It operates at 185 MHz, about a factor of 10 lower in frequency than the VLA/FIRST images you've been classifying at 1.4 GHz. The electron population that produces this emission is much older, which means they have a lower velocity and emit radio emission at lower frequencies.
    • the radio emission appears to be associated with the dust lane seen in optical images of the galaxy
    • Given the numbers of these types of galaxies, we can put a limit on how long radio galaxies live in this sort of phase: no more than 6% of their lifetimes. So it's a big deal to catch one of them in the act!!

    If anyone has questions, or is interested in reading the paper, I'd be happy to keep discussing it.

    Link to paper on the arXiv

    Posted

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

    Thanks Kyle.

    Although they don't say so, this seems to be another SDRAGN! 😃

    I found this particularly interesting:

    Highly extended radio sources hosted by galaxies with disks are very rare, with only six other clear examples known: [J2345-0449, Speca, PKS0131-36
    (NGC 612), Fornax A (NGC 1316), Centaurus A (NGC 5128), and 0313-192 (PMN J0315-906)]

    No mention of J1649+26 😮

    It would seem that we have essentially zero chance of finding anything like the fading lobes of NGC 1534 in RGZ, for quite a few reasons.

    All but one of "the six" have redshifts less than 0.08 (Speca, at 0.14, is the exception); unless there's something really strange about the local universe (to z ~0.1), there should be ~dozens of objects like these six out to z ~0.3 (more or less the SDSS limit of 'large disk galaxy' detectability). In turn, that suggests that we have already found at least a few of these, in the RGZ project so far; for example, as posted in the What are our VERY BEST 'hourglass sources associated with spirals'? thread.

    This newly discovered source is quite faint; the radio lobes' estimated 325 MHz luminosity is not quite 1024 W Hz-1. Yes, it seems we're lucky to have caught it as it fades; conversely, without knowing anything much about the luminosity density function for SDRAGNs, it's surely difficult to put any (robust) limits on things like duty cycle or evolution, right?

    Posted

  • ivywong by ivywong scientist, admin

    Yes, this is very true! Well spotted Jean! But this would possibly be the oldest SDRAGN relative to the ones that we will find because the emission typically found at such low-frequencies tend to be aged lobes.

    Posted

  • ivywong by ivywong scientist, admin

    Thanks for posting this paper Kyle! It is a very interesting find!

    Posted