Radio Galaxy Zoo Talk

Comment on object by the science team.

  • Gweilouk by Gweilouk

    When an object you have classified is looked at by one of the science team and they comment on it with "SDSS J130526.09+431228.2, z_ph=.241/0.2757" as has happened with an object, Image ARG0000z8n, I classified what does it mean?

    I can see the survey name SDSS and I assume the object name, J130256.... but is z redshift and have no value associated with it and what is the ph= reference?

    Posted

  • JeanTate by JeanTate

    "ph" means "photometric", in contrast to "sp" (spectroscopic).

    SDSS was primarily an imaging survey, and a very good one. From the estimated fluxes in the five SDSS bands (u, g, r, i, and z; only the middle three are used in SDSS images posted here) an estimated redshift can be calculated; it's often not very accurate, but certainly better than nothing. More lately, SDSS has been used primarily as a spectroscopic survey (actually several), and a great many galaxies have now had their redshifts estimated by the spectra (nearly always these estimates are good; occasionally, however, they are wrong).

    "SDSS Jnnnnnn.nn+/-nnnnnn.n" is an object's 'name' (well, one of them); the SDSS part refers to the survey in which it is named. The first set of numbers is its right ascension (RA), the second its declination (Dec), which are the celestial coordinates of the object (kinda like longitude and latitude). They are written as hhmmss.ss and +/-ddmmss.s, where hh is 'hour' (an archaic term, but still in almost universal use by astronomers! 😮 an 'hour' is 15 degrees), mm 'minutes' (actually, 'arcminutes'; it's an angular measure, not one of time), ss.s(s) 'seconds' (arcseconds). The "J" refers, I think, to "J2000.0", which is the zero-point for the (RA, Dec) pair; this is necessary because the Earth's axis of rotation is moving, due to precession and (nutation, though I think this is trivial).

    In the case of ARG0000z8n, HAndernach's comment means that he thinks the host of the doublelobe you identified is SDSS J130526.09+431228.2, which has a listed photometric redshift of 0.241/0.275. Here's that galaxy (you can find all the SDSS data on it by clicking on the link):

    enter image description here

    Hope this helps, and happy hunting! 😃

    Posted

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

    Hi Jean,

    Thanks for the explanation. 😃

    I thought it was the .ph part that was throwing me, which you have kindly explained however I was also not tying the RA/Dec co-ordinates to the objects name. In fact i was assuming it was following a naming convention similar to that used for optical objects.

    Is it fair to assume that if there's a spectrascopic value for the Redshift it's flagged z_sc or something similar? I have an understanding of RA and Dec from using my scope in the garden, though I am much lazier in my old age age and use a goto scope 😃

    Thanks again

    Paul

    Posted

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

    I also should have read the first line of your response more carefully... sp for spectrascopic. DOH!!! as Homer might say :-0

    Regards

    Paul

    Posted

  • ivywong by ivywong scientist, admin

    Thanks @JeanTate. Good catch!

    @Gweilouk, apologies about the acronyms and jargons... we sometimes get a little too comfortable with the jargon. Thank you very much for asking.

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  • Gweilouk by Gweilouk

    Hi Ivy,

    I work in IT so use Jargon all the time as well, but being an amateur and new to the results of Radio and IR observations so had a need to know what was what. I'm now looking for the objects I classify in SLOAN and flagging them if I find them.

    Another question, if there are no matching objects in SLOAN should I tag them as #nonOptical?

    Posted

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

    if there are no matching objects in SLOAN should I tag them as #nonOptical?

    There's no "official" list of hashtags; for cases where there is no apparent SDSS host, I use #nooptical

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

    Thanks Jean,

    I shall follow your lead and at least I'll be consistent with somebody else 😃

    Paul

    Posted

  • ivywong by ivywong scientist, admin

    Hi @Gweilouk and @JeanTate,

    #nooptical is fine. Note that there will be many #nooptical as many strong AGN live at high redshifts and the sensitivity of Sloan begins to drop at z~0.2.

    Thanks again,
    Ivy

    Posted