A project I'm working on involves getting data from SDSS DR12, and cross-matching it with NED, as described in Section 2 of this paper:

2.1 The sample

From the SDSS Data Release 12 (DR12, Alam et al. 2015), we extracted the first 33 643 QSOs with accurate spectroscopic redshifts (δz/z < 0.01), which span the magnitude range r = 14.667 − 22.618. We then used the source coordinates to obtain the nearest source within a 6 arc-second search radius in the NASA/IPAC Extragalactic Database (NED), which usually resulted in a single match. As well as obtaining the specific flux densities, we used the NED names to query the Wide-Field Infrared Survey Explorer (WISE, Wright et al. 2010) and the Two Micron All Sky Survey (2MASS, Skrutskie et al. 2006) databases. For each of the bands3, the photometric points which fell within ∆ log10 ν = ±0.05 of the central frequency of the band were averaged, with this then being converted to a magnitude.


I can find the SDSS DR12 on VizieR, and I know there are tools for cross-matching catalogs (I have TOPCAT) but I'm not sure of what steps to follow.

Can anyone give me some guidance on how to do the cross-match as per the paper, please?

  • $\begingroup$ I think this is a programming question, not an astronomy one. If you disagree, please elaborate in your question. The algorithm's idea is described in the quoted section. (and please quote text as text, not as image) $\endgroup$ Commented Jan 20, 2021 at 0:46
  • $\begingroup$ @planetmaker programming is an essential tool used by astronomers for astronomical research, it's incorrect and unhelpful to give the impression that questions about astronomy programming would not be on-topic here simply because it focuses on programming. Searching this site for "python" yields 379 posts for example. See also this recent comment. $\endgroup$
    – uhoh
    Commented Jan 20, 2021 at 0:57
  • $\begingroup$ @planetmaker What's even worse about that, this question is not about programming! TOPCAT is an already-written program; the question simply asks about using it as a tool to analyze astronomical data. $\endgroup$
    – uhoh
    Commented Jan 20, 2021 at 1:01
  • $\begingroup$ I'm not asking about programming -- I'm asking for help using a common astronomical tool, as @uhoh said. $\endgroup$
    – Jim421616
    Commented Jan 20, 2021 at 19:01


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