Radio Galaxy Zoo Talk

Great Example?

  • civilsparky by civilsparky

    Is this a black hole with big jets?

    Posted

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

    Welcome to Radio Galaxy Zoo, civilsparky!

    This is a classic #doublelobe with the faintest of radio emission from the core; one side (the lower, or south) has a nice lobe-and-jet structure, the other more a lobe without jet. The galaxy from which these radio features originate - the host - is SDSS J133538.98+073000.3, at the center of this image:

    enter image description here

    It doesn't have an SDSS spectrum, so we don't know its redshift for sure, but photometrically it's 0.446 ± 0.0574 (by one method) and 0.458 ± 0.1466 (by another). Using commonly accepted values for cosmological parameters, and Ned Wright's online calculator, its distance is ~8 billion lightyears.

    The engine which creates these giant radio structures is in the nucleus of the host galaxy, a supermassive black hole (an SMBH, with a mass of perhaps a billion times that of our own Sun) and accretion disk (very hot matter mostly on a one-way trip outside our universe); somehow - the details are poorly understood - magnetic fields and accretion disk plus the SMBH's mass and spin combine to launch two jets of ultra-relativistic particles, likely in the 'pole' directions (relative to the disc).

    This may be particularly interesting, and rare, for a reason I'll explain in my next post.

    Happy hunting! 😃

    Posted

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

    This may be particularly interesting, and rare, for a reason I'll explain in my next post.

    The red smudge which is the host of the nice doublelobes (plus faint core) looks somewhat elongated. Which means it may be an edge-on spiral, or at least a highly inclined one; either way, it could likely be NOT a boring elliptical.

    Per astronomer Ray Norris, we're on the lookout for these sorts of galaxies, as he explains in the thread Hourglass sources associated with spiral galaxies. If this is, indeed, a spiral (or at least a disk galaxy), it would be a most interesting find indeed! 😄

    How to tell if it's a disk galaxy, and not a boring elliptical?

    Its elongated shape is one way: true giant ellipticals (and giant ellipticals are the only ones we can see in SDSS images, at redshifts of ~0.4) aren't much out-of-round. Astronomers use a simple formula for expressing out-of-round quantitatively, ellipticity, defined as INT(10*(1-axis ratio)); 'axis ratio' is the ratio of the estimated length of the minor axis to that of the major axis (imagine the galaxy as an ellipse). The SDSS photometric pipeline provides estimates of these ratios (plus errors), assuming two models of light distribution. While the errors are large (and the u-band ones impossibly so), the ellipticities are all greater than 4, meaning this galaxy almost certainly is not a giant elliptical.

    Another method is the way the amount of light falls off, from the center. A standard way to do this is to fit the classic 'elliptical intensity profile' (called, for historical reasons, deVaucouleurs) and the exponential one (the disks of spirals galaxies often have such a profile), and see which fits best. The SDSS photometric pipeline does this automatically, and the result it pretty clear: the r and i band fits are exponential; the g band one a toss-up, and the u and z band ones deVaucouleurs. By far the strongest signals are in the r and i bands, and the u band has no signal.

    Yet another test, concentration, as measured by the inverse concentration ratio. This can be calculated from two sets of values provided by the pipeline, petroR50 and petroR90 (one pair for each band). Only two bands have values not dominated by errors, g and i; for both the key ratio says 'disk galaxy!' (0.576 and 0.548, respectively; the threshold is 0.385).

    So, civilsparky seems to have discovered a kind of galaxy I've been hunting for years now, a Huds (Huge distant spiral)[1]
    Yay! 😃

    [1] this post, in the GZ forum, contains one Letter I wrote on these

    Posted

  • JeanTate by JeanTate

    Sure looks like the host is the Huds Eos! 😃 E, model profile, and inverse concentration ratio later.

    enter image description here

    <enter image description here>

    Boilerplate: SDSS image per http://skyservice.pha.jhu.edu/DR10/ImgCutout/getjpeg.aspx, FIRST (red) contours derived from the FITS file produced using SkyView with Python code described in this RGZ Talk thread. Image center is the galaxy SDSS J133538.98+073000.3, near the ARG image (ARG0003a73; J2000.0). "z_ph" is an SDSS photometric redshift of the galaxy in the center.

    Posted