Radio Galaxy Zoo Talk

Disk galaxy smoke-rings?

  • DocR by DocR scientist

    A spectacular source. In a category by itself. Another coup for antikodon FIRST with SDSS
    !

    Posted

  • KWillett by KWillett scientist, admin, translator

    Incredible! It's amazing to see that sharp edge on the radio emission in the lower right; front of a shock?

    Posted

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

    Could these be two separate doublelobes/hourglasses? How best to determine whether or not they are related?

    Posted

  • DocR by DocR scientist

    @WizardHowl - my first reaction was the same as yours. But I really didn't see plausible candidates for the host IDs, in that case, and it would be extremely unlikely to have two unrelated, very unusual but similar to each other such sources on opposite sides of an unrelated bright galaxy. the similarities between the two lobes in brightness, size and structure just "too good to be true" for them to be unrelated.

    Posted

  • JeanTate by JeanTate

    From the comments, <- that way:

    yes, SDSS J160458.97+183547.7, a disc galaxy at z=.1222

    SDSS J160458.97+183547.7, a disk galaxy?!? 😮

    The PhotoObj fracDeV parameter values are 1, for all five filters (i.e. a deVaucouleurs profile is a better fit than an exponential one). True, this is a not especially good test, as I discovered some time ago (but Karen Masters had discovered it well before me).

    In terms of its ellipticity, this is an E3 galaxy*; if it were an E5, E6, or E7 we'd have good grounds for saying it had to be a disk galaxy (all giant ellipticals are E4, or less, per Buta (2011)). So this test is inconclusive.

    Four of the five inverse concentration ratios are less than 0.385, consistent with the galaxy being an elliptical (this SDSS webpage briefly introduces this test); the outlier is the u-band one, and petroR90 has an off-the-chart error, so it can be ignored. Again, elliptical.

    Zooites, in GZ1, classified this galaxy as Elliptical. I agree; to me it looks like an elliptical:

    enter image description here

    (Colors provide another test, albeit not an iron-clad one - there are 'red spirals' after all - I'll do that later).

    What am I missing?

    *it's an E5 in the u band, but the errors are huge

    Posted

  • HAndernach by HAndernach scientist, translator

    admittedly, my comment of 5 months ago "yes, SDSS J160458.97+183547.7, a disc galaxy at z=.1222"
    was not explicitly justified... I said this mainly because NED quotes
    a reference for this galaxy:
    2010MNRAS.406.1595F Fathi, K. et al: Scalelength of disc galaxies
    I hope this paper discusses in more detail what they did to conclude on
    a disky galaxy. The visual impression is certainly not conclusive.

    Posted

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

    Thanks! 😄

    Fathi+ 2010 selected 'disk galaxies' based on the parameter T in LEDA, values in the range [1,8]. T is a numerical mapping of Hubble morphological type, with 1 corresponding to Sa; lenticulars (S0) explicitly excluded.
    ETA: In their catalog, T ("Morphological type from LEDA") is given as 3.3±5.0 ("Morphological type Error").

    Today, HYPERLEDA gives online access to LEDA. SDSS J160458.97+183547.7 is PGC1564280 in LEDA; clicking on the Morph link in the record for this object, I get "The object you have requested is indexed in HyperLeda, but no data match your request".

    NED does not have an entry for "Classification", which is consistent with the result I got from querying LEDA.

    In Huertas-Company+, 2011, the spectral class is 0 ("totally dead and red" is my gloss; this is from ASK (Almeida+ 2010)), pE/S0 ("Probability of being early-type (E or S0)") is 0.90, with pE ("Probability of being elliptical") 0.33 and pS0 ("Probability of being S0 type") 0.57. pSab ("Probability of being Sa or Sb") is just 0.07 (this seems quite inconsistent with Fathi+ 2010/LEDA).

    In GZ1 (Lintott+ 2011), pE0 ("Fraction of votes for Elliptical categories following the debiasing procedure described in Section 3.1") is 0.924, and pS0 ("Fraction of votes for combined Spiral categories following the debiasing procedure described in Section 3.1") 0.076. GZ2 (Willett+ 2013) gives similar results.

    Of the six references NED gives for this galaxy, the only other one which may be relevant is Lin+ 2010. This puts SDSS J160458.97+183547.7 in class a ("HSB spots: opposite sides of RG; Central source: not HSB"), and gives rs ("Ratio of separation and total size") as 0.66. If it were plotted in Fig 6, it would be pretty normal*, except for (a/b)deV ("the axis ratio from the de Vaucouleurs profile"), which is a bit low (0.615±0.01).

    I wonder where LEDA got its value for T from, and why there's no value there now?

    ETA: I added the value for T, and its stated error, in Fathi+ 2010

    *I checked only a few parameters.

    Posted

  • JeanTate by JeanTate

    Fathi+ 2010 selected 'disk galaxies' based on the parameter T in LEDA, values in the range [1,8]. T is a numerical mapping of Hubble morphological type, with 1 corresponding to Sa; lenticulars (S0) explicitly excluded.
    ETA: In their catalog, T ("Morphological type from LEDA") is given as 3.3±5.0 ("Morphological type Error").

    I'm still trying to find out how LEDA derived the T value of 3.3±5.0; so far I'm stuck on "Calculation of homogenized astrophysical parameters". The method for T (t in LEDA) is described in de Vaucouleurs et al., 1991, 1997 (the first is RC3); but what's the actual source, for this galaxy? Is it RC3 itself?

    Anyway, T=3.3 is obviously wrong ... T=3 is Sb, and T=4 is Sbc, and this galaxy is nowhere near even an Sb, in its morphology ...

    Posted

  • zutopian by zutopian

    Jean informed today about following new paper.:

    A Catalogue of Two-Dimensional Photometric Decompositions in the SDSS-DR7 Spectroscopic Main Galaxy Sample: Preferred Models and Systematics, Meert+ 2014:
    http://arxiv.org/abs/1406.4179

    Is it useful for this case?

    Posted