The Quasars.org (QORG, 2004) catalogue can be downloaded from this page.

Note: QORG has been superseded by the Atlas of Radio/X-ray Associations (ARXA -- 2010 PASA, 27,283) which is here .

The catalogue is a flat ASCII file containing each object on one line, so the full quasars.org (QORG) catalogue contains 501761 lines.  A simple ASCII format is presented for easy access.   quick browse here     our paper (pre-publication version)

The full quasars.org data can be found in one catalogue (21Mb zipped):   download Master.zip     the ReadMe     browse subset

A condensed version, all objects, no more than 2 associations per object and omits supporting data (13Mb zipped):  
download Free-Lunch.zip     the ReadMe     browse subset

There are also subset catalogue files available for quasars.org objects bearing identifications from the literature, and QSO candidates which are hitherto unidentified objects for which we calculate odds of 40% to 99+% of being quasars:

119,816 Identified Objects (3Mb zipped)     browse subset
86,009 Quasar Candidates (2Mb zipped)     browse subset
A ReadMe for all four catalogues

How does the Quasars.org catalogue rate when tested against the subsequent SDSS Data Releases 2 through 7? The outcome is 94.9% accuracy in object selection, and useful correlation between the QORG-stated confidences and actual identification accuracy. See here for a discussion, analysis tables, and a full listing of the 36118 objects used in this comparison.

An integral part of building the Quasars.org catalogue was the need to shift ROSAT fields to their optically-optimized astrometric locations, using the whole-sky likelihood algorithm detailed in our paper . This typically involved shifts of 5-10 arcseconds. Researchers using ROSAT detections can use our field shifts to refine their own optical/ROSAT astrometric fits. Only shifted fields are included in these lists; many fields with few X-ray sources were left unshifted due to lack of good optical X-ray fits, but the large majority of X-ray sources are accounted for in these field shifts.

Field shifts for the HRI catalogue:     Individual listing     summary graph
Field shifts for the RASS catalogue:   Individual listing     summary graph
Field shifts for the PSPC catalogue:   Individual listing     summary graph
Field shifts for the WGA catalogue:   Individual listing     summary graph

Photometric calibration of the APM / USNO-A2.0 optical catalogues was necessary to improve the effectiveness of our all-sky likelihood algorithm which uses object colour as a classification. The USNO-A2.0 in particular displays large zero-point offsets in its object magnitudes; as an all-catalogue median, the USNO-A2.0 reports POSS-I O (B) as 0.8 mag too bright and POSS-I E (R) as 0.2 mag too bright. For a discussion which shows that this 0.6 mag colour offset is perforce a consequence of the calibration scheme adopted for the USNO-A2.0, see here. The USNO-A2.0 also displays UKST R as 0.9 mag too bright and UKST Bj as 0.7 too bright, as an all-catalogue median.

Full plate-by-plate photometric calibration of the entire APM and USNO-A2.0 is here
Quasars.org plate-by-plate boundaries, depths & object totals is here

Objects reported in star catalogues as stars and as galaxies/quasars elsewhere are here
Joint-source comparisons of XMM1 vs ChaMP initial releases are here
Old QSO surveys with identifiable mean astrometric or photometric offsets are here

This section only for the hard-core.

Performance of the Quasars.org likelihood algorithm against the ROSAT catalogues as adjudged by XMM1/ChaMP-determined optical targets here
Performance of the Quasars.org double-lobe detection algorithm against the 3CRR catalogue here
All-Sky optical bin counts used as the background for likelihood calculations here
Likelihood background bin counts (zipped) for   HRI   RASS   PSPC   WGA   FIRST   NVSS   SUMSS
Optical fields astrometically mis-alligned to Radio catalogues, by field (zipped) here
Summary graphs of ROSAT field shifts before cutoffs applied   HRI   RASS   PSPC   WGA
Characteristics of "best" ROSAT field shifts at various shift distances here

last changed 16-Jan-05 Eric Flesch