Galaxy Zoo Talk

Arm number, and Spiral emission on the disc axis

  • Peter_Jackson by Peter_Jackson

    common to many closely studied galaxies this seems to have a form of axial emission stream creating an expanding helix or 3D spiral form, looking like to series of feint red loops from this angle. (the Milky Way has significant axial outflows though a spiral pattern is difficult to resolve).

    The answer given to the question on spiral arms (4) doesn't quite match the graphic provided because, as also common, the ares are somewhat paired. They may then be termed 2 arms, one from each end of the bar, but each split into 2. Again the Milky way arms can also be loosely resolved into this morphology.

    There's much established evidence and analysis of these characteristics but the GZ graphics and choices to seem based on rather older theoretical assumptions which can tend to misguide and perpetuate poor understanding.

    Posted

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

    this seems to have a form of axial emission stream creating an expanding helix or 3D spiral form, looking like to series of feint red loops from this angle.

    I think those are all artifacts, unique to DECaLS.

    There's much established evidence and analysis of these characteristics but the GZ graphics and choices to seem based on rather older theoretical assumptions which can tend to misguide and perpetuate poor understanding

    I suspect this is a problem every Zooniverse astronomy-related project faces, in one way or another (in RGZ, for example, there's something similar re 'double lobes'). In part, I think it may be partly due to the inherent conservatism of morphology classification schemes ... for example, in the main GZ2 paper, there's a shorthand 'gz2_class' which seems to rely heavily on the Hubble scheme (note: although "We emphasise that the intent is not to create a new classification system; rather, this is only a convenient shorthand for interpreting portions of the GZ2 results", it will almost certainly be used, by some, as exactly that).

    Posted