Galaxy Zoo Talk

Star / galaxy puzzle

  • Ghost_Sheep_SWR by Ghost_Sheep_SWR

    AGZ000e2iu and AGZ000e2it

    I suspect this is a collisional ring galaxy, but I'm a little bit confused about the yellow object at 11 o'clock near the nucleus. Is it a foreground star or perhaps associated with the ringed galaxy?

    enter image description here

    If I'm correct this object is also ID'd as *2dFGRS N309Z271 in NED. When I use the link in that NED page to SDSS it also brings me to this object, which classifies as 'star'. It has a NED redshift of z=0.0004 +/- 0.000297, so a pretty big error margin. But z=0.0004 is also way too high for a MW star isn't it (should be close to 0)?

    There is also one essential note in NED:

    ESSENTIAL NOTE for 2dFGRS N309Z271
    This is a galaxy with a neighboring star; the 2dF redshift is for the star.

    enter image description here spectrum target

    enter image description here spectrum preview

    NED page http://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Obj_id&objid=1089038&objname=3&img_stamp=YES&hconst=73.0&omegam=0.27&omegav=0.73&corr_z=1

    SDSS page http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?id=1237671141480595494


    Foreground star with a bad redshift or are the other two 'galaxy' designations correct?

    Posted

  • zoob1172 by zoob1172

    Maybe the emoticons will be changed to morphology classification types to help new classifiers. * will be a choice.

    Posted

  • CeciliaB by CeciliaB

    Actually, my first thought was that the ringed galaxy looked like a collisional ring galaxy.

    I'm sure that foreground stars have z=0. Could the yellow object be a nearby, compact galaxy with a low z=0.0004, overlapping the ringed galaxy? In the GAMA image the yellow object isn't quite round and does look as if it is much nearer to us than the slightly blurred ringed galaxy.

    EDIT: ..but it doesn't look much like a galaxy.

    Posted

  • Ghost_Sheep_SWR by Ghost_Sheep_SWR in response to CeciliaB's comment.

    Yeah when I suspect it fits in one of the GZ collections I'll just tag it and leave it to the moderators to judge. Really does look like a collisional ring galaxy but without a suspect galaxy. If yellowball is indeed a star or closer to us the perpetrator might be hiding behind it.


    Yes exactly;

    It has this oblong shape in the GAMA image while the brighter foreground star is just perfectly round. In combination with the strange spectrum redshift makes you wonder.

    But also very likely to be 'just' a foreground star because it doesn't look like a galaxy or anything else really...

    Posted

  • zoob1172 by zoob1172

    May I have your authority on "collision ring" objects? The ONE that distinguishes it/them from other more/less 'violent' types.

    Posted

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

    Assuming the redshift is indeed 0.0004 (how many km/s is that, by the way?), what do you think the more prominent emission and absorption lines in the spectrum are?

    The spectra of ETG (early type galaxies, a.k.a. ellipticals and lenticulars) nearly always have prominent "H" and "K" lines, as well as a "400nm cliff"; can you see any of these features in the spectrum? If you compare it with the SDSS templates (yeah, taken by different equipment, but still), and assuming it's a star, what's its likely spectral class?

    Posted

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

    Good plan, thanks for the info. Have to see when I can get busy with this. Such a high error margin is probably a big red flag, but interesting.

    If I understand correctly there is a dedicated SDSS spectrum template page?

    Posted

  • Ghost_Sheep_SWR by Ghost_Sheep_SWR

    I'' too confused now to examine the 'galaxy' spectrum properly. I think there is a position mix-up because the actual spectrum position is in between the galaxy with GAMA specz z=0.10685 and the big bright foreground star at 10 o'clock, but not on the actual yellow object.

    So the redshift of z ~ 0.0003 - 0.0004 doesn't makes sense at all, although it has a good quality marker; redshift quality = 4 (reliable redshifts have quality≥3) but has a NED redshift of 0.000400 +/- 0.000297 and NED ESSENTIAL NOTE: This is a galaxy with a neighboring star; the 2dF redshift is for the star.

    2dFGRS location of the spectrum: 11:42:39.31 -0:49:25.3 J2000.0

    Here is the object page of 2dFGRS N309Z271 : http://magnum.anu.edu.au/TDFgg-cgi-bin/w3-msql/TDFgg/display.html?fits=858/292772.fits

    and the spectrum image

    enter image description here


    And then there is also the LAMOST DR2 spectrum with exact location on the yellow object RA,Dec175.6627340000 -00.8236720000 which looks like a foreground star spectrum and has LAMOST DR2 designation ''STAR'.

    enter image description here

    Spectrum location: http://vizier.u-strasbg.fr/vizier/vizgraph.gml?-s=V/149&-i=.graph_sql&ObsId= 48110215&Target=J114239.05-004925.2&file=F5601204/spec-56012-F5601204_sp10-215.fits

    VizieR LAMOST DR2 SDSS J114239.05-004925.2 object page: http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ595ccc65a6b9&-out.add=.&-source=V/149/dr2&recno=811507


    So for now I think it is just a mixup with a weird 2dFGRS spectrum location, the oblong shape in the GAMA image is an optical artifact and the LAMOST DR2 spectrum is the correct one for the object (which is a MW star). Maybe look at the 2dFGRS spectrum better later on.

    Posted