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Title: Nway--An accurate algorithm to pair sources simultaneously between N catalogs

Contact person: Mara Salvato (mara@mpe.mpg.de)

Interested/contributing people: Johannes Buchner, Tamas Budavari, Tom Dwelly, Andrea Merloni,Marcella Brusa +Interested people

Description: The  increasing number of surveys available at any wavelength is allowing the construction of Spectral Energy Distribution (SED) for any  kind of astrophysical object. However, a)different surveys/instruments have different positional accuracy and resolution  and often are not registered to the same reference system and b) surveys's depth that do not match each other and depending on its redshift and SED, a given source might or might not be detected in a survey. All this makes the pairing of sources among catalogs not trivial.}{ We propose a new algorithm that combine  the best of Bayesian and frequentist methods. We extend on the work presented in  \citet {Budavari:2008qy}, where we weight the probability that 2 or more sources are associated by one or more priors. We tested the algorithm computing the association between X-ray detected AGN (XMM- and Chandra-COSMOS) and optical and near-infrared sources, simultaneously. When comparing with  literature where Maximum Likelihood ratio methods have been used, we find an agreement up to 95\%. For the remaining 5\% of the case we can not access whether either the new code or the literature is providing the correct associations.  We finally used the code to compute the optical and mid-infrared counterparts to the Rosat all-sky faint sources. In this paper we release the code and the new catalog of counterparts. 

Data used: ROSAT, XMM- and Chandra COSMOS,  SDSS, WISE, COSMOS photmetry

Project conclusion / Publication date: We aim for submission by Dec 2014 / Jan 2015.