CSC 2 Crossmatches
This page contains links and short descriptions of the tables of crossmatches between versions of the Chandra Source Catalog 2 and catalogs of sources from several multi-wavelength surveys. All crossmatches have been performed with a Bayesian method developed by Budavari & Szalay (2008) as implemented and extended by either A. Rots (2020) in the Xmatch code that takes into account local source density as well as both error ellipses and raw-size ellipses of the sources, or in the NWAY code (Salvato et al 2018).
CSC 2.0 sources are extracted from the CSC 2.0 Master Sources table. For each crossmatched source pair the match probability (between 0.0 and 1.0), match type (E when positional error ellipse is used, R if source raw size is used) and match grade (D for definite matches, L for likely matches) are provided. The details on these columns can be found here. In addition, ambiguous matches are provided in separate tables.
PRELIMINARY CSC 2.1 Production Current Database Crossmatches and SDSS Spectra
Using the NWAY algorithm, we have crossmatched the set of X-ray sources extracted from the CSC 2.1 production current database on 14 November 2022 (389k sources) to four catalogs—Gaia DR3, Legacy Survey DR10, PanSTARRS-1, and 2MASS, finding counterparts for 229k CSC 2.1 production current database sources. Cross-matching this table with SDSS DR17 spectroscopy yields more than 17k objects with SDSS spectra, including pipeline classifications and radial velocities. The resulting catalog lists a subset of X-ray information for these sources, includes catalog IDs, positions and magnitudes for all optical/IR matches. We present a README file describing the catalog, and the cross-match catalog itself in FITS and CSV format.
Because this cross-match is performed using the preliminary CSC 2.1 production current database while processing continues, the user should be aware that a few percent of the matches may be wrong, have incorrect positions and/or position errors, or may be rejected entirely by catalog quality assurance when the final CSC 2.1 catalog is released.
A crossmatched table of 188k sources has been submitted to the SDSS-V project as potential targets for spectroscopy. Those that are observed will be matched to upcoming CSC 2.1 sources after the SDSS-V spectral data become public.
CSC 2.0-SDSS unambiguous matches
The table (CSV format) linked below contains the pairs of unambiguous matches between CSC 2.0 and the SDSS DR15 catalog using the Xmatch algorithm. CSC 2.0 sources are from the "Master Sources" table. The SDSS DR15 are from the "Star" or "Galaxy" views within the two rectangular boxes:
- 120° < RA < 240° and 0° < Dec < 60°
- -30° < RA < 30° and -5° < Dec < 30°
|CSC 2.0 name, 2CXO JHHMMSS.s+DDMMSS (name)
|CSC source type (P for point sources, X for extended compact sources < 1 arcmin)
|CSC 2.0 Right Ascension (ICRS) (ra)
|CSC 2.0 Declination (ICRS) (dec)
|CSC 2.0 semi-major axis of the 95% confidence level position error ellipse (errellipser0)
|CSC 2.0 semi-minor axis of the 95% confidence level position error ellipse (errellipser1)
|CSC 2.0 position angle relative to the local true N of the major axis of the 95% confidence level position error ellipse
|CSC 2.0 semi-major axis of the 1σ ellipse fitted to the source as seen in the image
|CSC 2.0 semi-minor axis of the 1σ ellipse fitted to the source as seen in the image
|CSC 2.0 position angle of the 1σ ellipse fitted to the source as seen in the image
|CSC 2.0 match major axis of the ellipse used for the crossmatch
|CSC 2.0 match semi-minor of the ellipse used for the crossmatch
|CSC 2.0 match position angle of the ellipse used for the crossmatch
|SDSS unique identifier
|SDSS Type classification (type) (S for stars, G for galaxies)
|SDSS Right Ascension (J2000)
|SDSS Declination (J2000)
|SDSS semi-major axis of the 1σ error ellipse (SDSS semi-major axis of the 1σ error ellipse, i.e larger of raErr and decErr [arcsec])
|SDSS semi-minor axis of the 1σ error ellipse (SDSS semi-minor axis of the 1σ error ellipse, i.e smaller between raErr and decErr [arcsec])
|SDSS position angle (local true N) of the 1σ error ellipse with major and minor axes
|SDSS semi-major axis of the source raw 1σ size ellipse, calculated from adaptive moments
|SDSS semi-minor axis of the source raw 1σ size ellipse, calculated from adaptive moments
|SDSS position angle of the source raw 1σ size ellipse, calculated from adaptive moments
|SDSS match semi-major of the ellipse used for the crossmatch
|SDSS match semi-minor of the ellipse used for the crossmatch
|SDSS match position relative to the local true N of the ellipse used for the crossmatch
|Angular distance between CSC 2.0 and SDSS DR15 sources
|Match type (E when positional error ellipse is used, R if source raw size is used)
|Match grade (D for definite matches, L for likely matches)
CSC 2.0-SDSS ambiguous matches
The two tab-delimited tables linked below contain the sources from each catalog that have multiple accepted matches in the other catalog (i.e. CSC 2.0 sources with multiple SDSS crossmatches and vice versa) using the Xmatch algorithm. Please notice that these ambiguous crossmatches are not to be confused with ambiguous matches between per-observation sources and master sources internal to the CSC 2.0 catalog. The ambiguous matches tables (CSV format) contain a variable number of columns (but never less than three) with compound formats described below:
- The first column (format %s (%c):) contains the IDs of that catalog's sources that have multiple matches, followed by a space, a single character in parentheses indicating the source's type, and a colon.
All subsequent columns have a single compound format (%s (%c %5.3f %5.3f %c)), containing:
- the ID of a matching source from the other catalog, followed by a space and an opening parenthesis
- a single character indicating that source's type, followed by a space
- the separation of the matched pair, followed by a space
- the match probability, followed by a space
- the match type (E for error ellipse, R for raw size ellipse), followed by a closing parenthesis