CSC Crossmatches
Introduction
This page contains short descriptions of the crossmatch tables between the Chandra Source Catalog and other multi-wavelength catalogs. The CSC sources are extracted from the Master Sources table. For each counterpart, the match probability (between 0.0 and 1.0) and separation (in arcsec) are given so that users may apply their own selection criteria appropriate for their goals.
PRELIMINARY CSC 2.1 Database Crossmatches for SDSS-V Target Selection and SDSS Spectra
Using the NWAY algorithm, we have crossmatched the X-ray sources extracted from the CSC 2.1 production database on 14 November 2022 (389k sources) to four optical and near-IR catalogs—Gaia DR3, Legacy Survey DR10, PanSTARRS-1, and 2MASS— finding counterparts for 229k sources. The resulting matched catalog lists a subset of X-ray information, catalog IDs, positions, and magnitudes for all optical/IR matches. Cross-matching this table with SDSS DR17 spectroscopy yields about 17k objects for which SDSS spectra, classifications, and radial velocities are given. We present a README file describing the catalog, and the cross-match catalog itself in FITS and CSV format.
A crossmatched table of 188k sources has been submitted to the SDSS-V project as potential targets for spectroscopy.
CSC 2.0-SDSS DR15 Crossmatches
All crossmatches have been performed with a Bayesian method developed by Budavari & Szalay (2008) as implemented and extended by 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. 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 are provided in the Xmatch quick summary. In addition, ambiguous matches are provided in separate tables.
Unambiguous Matches
The table (CSV format) linked below contains the pairs of unambiguous matches between CSC 2,9; 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°
The descriptions of all the columns provided in the table can be found below. A web-based query tool for the table provided by the VizieR service can be found here.
Files:
Final CSC2.0 - SDSS matches (CSV, TSV)
CSC 2.0–SDSS Crossmatch Column Descriptions
| Column Name | Class | Description | |
|---|---|---|---|
| 1 | CSC2_ID | String | CSC name, 2CXO JHHMMSS.s+DDMMSS (name) |
| 2 | CSC2_Type | String | CSC source type (P for point sources, X for extended compact sources < 1 arcmin) |
| 3 | CSC2_RA | Double | CSC Right Ascension (ICRS) (ra) |
| 4 | CSC2_Dec | Double | CSC Declination (ICRS) (dec) |
| 5 | CSC2_ErrMaj_95% | Double | CSC semi-major axis of the 95% confidence level position error ellipse (errellipser0) |
| 6 | CSC2_ErrMin_95% | Double | CSC semi-minor axis of the 95% confidence level position error ellipse (errellipser1) |
| 7 | CSC2_ErrPA | Double | CSC position angle relative to the local true N of the major axis of the 95% confidence level position error ellipse |
| 8 | CSC2_RawMaj_1-sigma | Double | CSC semi-major axis of the 1σ ellipse fitted to the source as seen in the image |
| 9 | CSC2_RawMin_1-sigma | Double | CSC semi-minor axis of the 1σ ellipse fitted to the source as seen in the image |
| 10 | CSC2_RawPA | Double | CSC position angle of the 1σ ellipse fitted to the source as seen in the image |
| 11 | CSC2_MatchMaj_1-sigma | Double | CSC match major axis of the ellipse used for the crossmatch |
| 12 | CSC2_MatchMin_1-sigma | Double | CSC match semi-minor of the ellipse used for the crossmatch |
| 13 | CSC2_MatchPA_1-sigma | Double | CSC match position angle of the ellipse used for the crossmatch |
| 14 | SDSSDR15_ID | Long | SDSS unique identifier |
| 15 | SDSSDR15_Type | String | SDSS Type classification (type) (S for stars, G for galaxies) |
| 16 | SDSSDR15_RA | Double | SDSS Right Ascension (J2000) |
| 17 | SDSSDR15_Dec | Double | SDSS Declination (J2000) |
| 18 | SDSSDR15_ErrMaj_1-sigma | Double | 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]) |
| 19 | SDSSDR15_ErrMin_1-sigma | Double | 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]) |
| 20 | SDSSDR15_ErrPA_1-sigma | Float | SDSS position angle (local true N) of the 1σ error ellipse with major and minor axes |
| 21 | SDSSDR15_RawMaj_1-sigma | Double | SDSS semi-major axis of the source raw 1σ size ellipse, calculated from adaptive moments |
| 22 | SDSSDR15_RawMin_1-sigma | Double | SDSS semi-minor axis of the source raw 1σ size ellipse, calculated from adaptive moments |
| 23 | SDSSDR15_RawPa_1-sigma | Double | SDSS position angle of the source raw 1σ size ellipse, calculated from adaptive moments |
| 24 | SDSSDR15_MatchMaj_1-sigma | Double | SDSS match semi-major of the ellipse used for the crossmatch |
| 25 | SDSSDR15_MatchMin_1-sigma | Double | SDSS match semi-minor of the ellipse used for the crossmatch |
| 26 | SDSSDR15_MatchPA_1-sigma | Double | SDSS match position relative to the local true N of the ellipse used for the crossmatch |
| 27 | CSC2-SDSSDR15_separation | Double | Angular distance between CSC and SDSS DR15 sources |
| 28 | Match_probability | Double | Match probability |
| 29 | Match_type | String | Match type (E when positional error ellipse is used, R if source raw size is used) |
| 30 | Match_grade | String | Match grade (D for definite matches, L for likely matches) |
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 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 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