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MILLIQUAS - Million Quasars Catalog, Version 7.2 (2 May 2021)



This table contains the Million Quasars (MILLIQUAS) Catalog, Version 7.2 (2 May 2021). It is a compendium of 829,666 type-I QSOs and AGN, largely complete from the literature to 30 April 2021, including the SDSS-DR16Q and VLASS radio catalogs. Also included are 703,348 quasar candidates which are calculated as 60-100% likely to be quasars, including 225,051 which are radio/X-ray associated. Type-II and BL Lac objects are also included, bringing the total count to 1,573,824. Gaia-DR2 astrometry is used where available, amounting to ~66% of all objects. Objects have been de-duplicated across multiple source catalogs.

Low-confidence/quality or questionable objects (so deemed by their researchers) are not included in Milliquas. Additional quality cuts can be applied as detailed in the HMQ paper (Flesch 2015,PASA,32,10). Full QSO/AGN classification is via spectral lines, thus hidden/occluded objects may be absent from Milliquas. Two NIQs offset <2 arcsecs can be reported as a single object if within the same host. The author's aim here is to present one unique reliable object per each data row.

This version has the following changes from the previous edition:

(1) Quasars added from publications to 30 April 2021.
(2) The VLASS Quick Look radio catalog is included, which adds 34189 new
    radio core associations and 6793 probable double radio lobe associations.
(3) Ongoing audits of SDSS & LAMOST quasars have led to a few additions and
    drops. Some WISEA-supported SDSS/LAMOST pipeline quasars are now accepted
    which were otherwise marginal. Also, some likely galaxies have been
The contents are relatively simple; each object is shown as one entry with the sky coordinates, its original name, object class, red and blue optical magnitudes, PSF class, redshift, the citations for the name and redshift, and up to four radio/X-ray identifiers where applicable.

Questions/comments/praise/complaints may be directed to Eric Flesch at If you use this catalog in published research, the author requests that you please cite it. The paper for Milliquas is at Please cite as Milliquas v7.2, Flesch, E.W. 2021, arXiv:2105.12985 or as the refereed citation, Milliquas v7.2 (2021) update, Flesch, E.W. 2015,PASA,32,10.

The confirmed quasars of this catalog (to Jan 2015) were published as the Half Million Quasars (HMQ) catalog: Flesch E., 2015,PASA,32,10. Note however that Milliquas uses optical sky data from ASP (2017,PASA,34,25) whereas the HMQ used optical sky data from QORG (2004,A&A,427,387) Appendix A.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

This research has made use of the SIMBAD database and cross-match service (to obtain Gaia DR2 data) provided by CDS, Strasbourg, France.


Flesch, E.
    The Million Quasars (MILLIQUAS) Catalog, Version 7.2 (2 May 2021)
See also:
   APM Catalog    
   USNO-A/B Catalogs
   NVSS Catalog   
   FIRST Catalog  
   SUMSS Catalog  
   MGPS Catalog   
   ROSAT Catalogs 
   1WGA Catalog   
   Chandra Source Catalog
   XAssist Home Page
   XMM-Newton Catalog
   XMM-Newton Slew Survey


This table was updated by the HEASARC in May 2021 based on a machine-readable catalog obtained from the author's MILLIQUAS website at

Version Log

     0.1  22Apr09
     0.3   6May09  Added a radio identifier and an X-ray identifier.
     0.5  11May09  Added 30816 objects from newly calculated associations to
                         XMM, Chandra and SUMSS detections, plus some tweaks.
                         Also added QSO probability % for non-confirmed QSOs.
     0.8  22Jun09  Added Chandra Source Catalog 1.0 (2009).
     1.0   3Aug09  Extensive de-duplication. XMM Slew Catalog data added.
     1.4  20Aug09  Misc fixes in the de-duplications.
     1.5  29Aug09  Used XMM Slew Catalog v1.3
     2.0  14Jun10  Used XMM Slew Catalog v1.4, XMM3, and XAssist4.
     2.1  17Aug10  Removed 8627 NELGs masquerading as AGNe.
     2.2   7Jan11  About 10,000 AGNe from the previous edition are now
                   presented as QSOs. 796 AGNe mistakenly expunged in 2.1
                   have been restored.
     2.3   5Mar11  SDSS DR-8 and BOSS targets have been included and the
                   threshold for inclusions of candidates has been raised
                   from 60% to 70%.
     2.4   5Jun11  Improved QSO-likelihood calculation for the BOSS targets,
                   so 17% of previously included BOSS targets drop out.
                   Newly included data from several sources (see above).
     2.5  20Jul11  Some de-duplication of quasars which were discovered prior
                   to 1990, 200 recent NED quasars added, some radio/X-ray
                   associations to USNO-B optical data added.
     2.6  10Sep11  The USNO-B catalog has been added and hard-deduplicated
                   against APM and SDSS data to make a background pool of
                   1.04 billion optical objects. Also, about 12 million
                   orphaned one-color APM objects have been removed. There
                   are consequently improvements in this catalog's optical
                   selections and astrometry without changing the net totals
                   much. XMM Slew 1.5 catalog added. Some further astrometric
                   fixes and de-duplications of early quasars.
     2.7   5Nov11  New quasar publications to 4 November 2011 were added,
                   and a few fixes on individual objects incorporated.
     2.8  29Jan12  Completed the fixes of non-astrometric relic data from the
                   Veron-Cetty & Veron 13th edition. About 150 other fixes.
                   Quasars compilation updated through 27 January 2012.
     2.9   2Apr12  Data brought up to publications as of 31 March 2012,
                   about 50 astrometric fixes done, and the new FIRST radio
                   catalog, 12Feb16 version, incorporated.
     2.10  6Aug12  Data brought up to publications as of 31 July 2012, including
                   the SDSS-DR9 release, XAssist XMM-Newton and Chandra X-ray
                   data updated to 30 June 2012; as this is a catalog for
                   type I (broad-line) objects, 1870 Seyfert-2s, 532 LINERs,
                   and 6 NELGs were removed, but BL Lacs were retained as
                   unconstrained emission objects.
     3.0   9Sep12  Data brought up to publications as of 31 August 2012.
                   Redshifts are calculated for the XDQSO photometric quasar
                   candidates. Fixed issues with 30 DEEP2 object. Separated
                   out 15 SDSS-DR9 object that had been conflated with others.
                   QSO-AGN separator restored to that used through v2.9, thus
                   ~5000 QSOs were re-classified as AGNe. AGNe historic names
                   sourced from the Principal Galaxy Catalogue.
     3.1  22Oct12  Quasar data brought up to publications as of 20 Oct. 2012,
                   including the new DR9 Quasar catalog (Paris I., 2012,
     3.2  10Feb13  Quasar data brought up to publications as of 9 Feb. 2013.
                   MMT quasar positions fixed, and made a few small
                   miscellaneous fixes.
     3.3   7Apr13  Quasar data brought up to publications as at 6 April 2013.
                   Added 713 new quasars from Palanque-Delabrouille et al.
                   (2013, A&A, 551, A29). Included SWIRE data, consisting of
                   117 confirmed quasars and >20K photometric quasars from
                   Rowan-Robinson et al. (2013, MNRAS, 428, 1958).
                   Located 8 QSOs that were previously uncertainly located
                   and removed 1 that had no credible candidates. Removed 26
                   SDSS-DR9 quasars after inspection showed they were only
                   artifacts. Removed 144 questionable quasars from Iovino
                   et al. (1996, A&AS, 119, 265). Removed 8 blazars classified
                   as white dwarfs by the SDSS DR7 WD Cat (2013,ApJS,204,5).
                   Miscellaneous: 4 moves, 2 de-dups, and 4 deletions found
                   after extensive trawling.
     3.4  11Jul13  Quasar data brought up to publications as at 11 July 2013.
                   The author's paper (2013, PASA, 30, 4) marked 9 QSOs as
                   uncertainly located. Of those:
                   (a) Q 0112-27 is finally sited at J011517.2-271223,
                       courtesy Cyril Hazard.
                   (b) Q 0752+617 is moved to J075646.6+613639, r=16.9, b=17.4,
                      as a better fit with its co-published quasar (NOTNI 16,
                      r=16.7, b=17.2).
                   Added 92 new quasars from Cyril Hazard. Q 1409+732 was found
                   to be sited on a plate flaw, and is now moved one arcmin
                   due East to perfect optical fit at J141003.2+725939,
                   r=19.3, b>22. XAssist v4 XMM-Newton & Chandra X-ray data
                   updated to 30-June-2013.
     3.5  11Aug13  Quasar data brought up to publications as at 10 August 2013,
                   including SDSS-DR10. Note that the DR10 is an automated
                   catalog, so its object classifications are not as
                   trustworthy as manual classifications. Thus, earlier
                   manual classifications are retained over DR10
                   classifications. XMM-Newton X-ray data updated to 3XMM-DR4
                   version (24-July-2013). FIRST radio data updated to
                   13Jun05 version (05-June-2013).
     3.6  23Oct13  Quasar data brought up to publications as at 22 October
                   2013. Two additional columns of radio/X-ray detections
                   were added. This is so that any radio lobes will always be
                   fully displayed, and extra detections from other source
                   catalogs give a sense of fuller coverage. 158 additional
                   quasars were added from SDSS-DR10. These were flagged as
                   bad astrometry, but they are confirmed by the author's
                   optical background database. Photometric quasar candidates
                   from surveys other than NBCKDE and XDQSO, e.g., SWIRE,
                   have been dropped because much of their yield are type 2.
                   This includes Palanque-Delabrouille et al.
                   (2011,A&A,530,122), which has been well investigated
                   spectroscopically and its residue thus less likely to be
                   QSOs. X-ray detections from the Champ2 catalog, Kim M. et
                   al., 2007,ApJS,169,401 have been removed. It's a small
                   catalog which, unlike others, does not present its raw
                   astrometry needed for calculating optical solutions. The
                   Veron quasar catalog v13 (2010 A&A,518A,10) included some
                   objects denoted as non-quasars by their discovery papers,
                   and the following have been removed as a result:
                   (a) 484 emission-line galaxies (ELGs) of z<0.46 from
                       Schneider/Schmidt/Gunn 1994,AJ,107,1245, incorporated
                       as QSOs by VCV13;
                   (b) 55 ELGs of Schneider/Schmidt/Gunn 1999,AJ,117,40;
                   (c) 58 galaxies from 2dF-GRS (Colless M. et al.,
                       astro-ph/0306581); and
                   (d) 41 galaxies from La Franca F. et al.,
                   A few positional fixes, de-duplications, and removals of
     3.7  26Nov13  Quasar data brought up to publications as at 26 November
                   2013, including the SDSS DR10Q release by Isabelle Paris
                   et al., 2013 arXiv:1311.4870. 318 SDSS "quasars" of
                   auto-redshift>4 which were not subsequently confirmed by
                   visual inspection are removed as bogus (communication Adam
                   Myers). The Veron quasar catalog v13 (2010 A&A,518A,10)
                   flagged some objects as questionable in their "spec"
                   field. These have unclear spectra or are described as
                   "possible" by their discovery papers. 178 of these are
                   removed, and 52 such BL Lacs with redshift>0.5 are
                   re-classed to AGNs. Some positional fixes and
                   de-duplications of individual objects.
     3.8  16Feb14  Quasar data brought up to publications as at 15 February
                   2014. NBCKDE and BOSS quasar likelihoods have been
                   calibrated against the DR10Q (Paris I. et al., 2013
                   arXiv:1311.4870) classifications. The Swift X-ray Point
                   Source catalog (Evans P.A. et al., 2014,ApJS,210,8) is added
                   to the background data, resulting in 12604 associations.
                   110 SDSS-DR10 automated survey objects are removed as
                   artifacts. De-duplication of radio/X-ray detections
     3.9  30Jun14  Quasar data brought up to publications as at 30 June 2014.
                   The XMM-Newton Slew Survey source catalog release 1.6 was
                   added to X-ray data. The 1SXPS X-ray detections were being
                   dropped; this was fixed and 21268 were included as a
                   result. The Veron-Cetty & Veron Quasar Catalog (VCV) 13th
                   edition (2010,A&A,518,10) was fully mapped into optical;
                   corrections from this were incorporated.
     4.0  05Aug14  Quasar data brought up to publications as at 5 August 2014.
                   The threshold for inclusion of QSO candidates was raised
                   to 80% confidence. This resulted in the loss of ~240,000
                   objects from v3.9, but it improved the confidence of use.
                   XAssist v4 XMM-Newton and Chandra X-ray data was updated
                   to 21-July-2014. 98 entries were found to be type II or
                   not quasars, and so removed. The catalog layout was
                   changed to conform better to the NED guide "Best Practices
                   for Data Publication" by Marion Schmitz et al. (v1.2, 2013)
                   in these ways: (a) all citations were changed to original
                   discovery papers and no longer to VCV 13th edition or to
                   NED and discovery citations are now indexed in a separate
                   file; (b) quasar and radio/X-ray names which used to run
                   together have been corrected to adhere to naming standards.
     4.1  20Oct14  Quasar data brought up to publications as at 5 October 2014.
                   The input values of RA and DEC used for this table were
                   given in degrees rather than sexagesimal. Type 2 objects
                   were included for the convenience of the users, but
                   completeness of these is only about 95%. The type I
                   objects are believed to be 100% complete from the
                   literature. About 3000 SDSS "quasars" were removed as not
                   quasars. These were auto-objects which were not taken up
                   by the manual Paris files, and which were not given a
                   subclass by the SDSS pipeline -- thus, the lowest quality
                   objects. Another 2000 were reclassified as AGN or type 2
                   in this catalog. VCV mis-copied the redshifts from 2008
                   A&A,488,417 -- now fixed. QSOs & AGN re-partitioned by psf
                   class and modified luminosity equation. Miscellaneous
                   tweaks and fixes done when revealed by publication-related
     4.2  06Dec14  Quasar data brought up to publications as at 6 December
                   2014. SDSS DR10/DR10Q and DR7/DR7Q data were reprocessed,
                   yielding a few more quasars and using the DR10Q redshifts
                   more as the current standard. Further adjustments were
                   made to the luminosity equation separating QSOs from AGN,
                   resulting in about 2000 AGN reclassified as QSOs. 18 new
                   quasars from Dan Weedman, based on his re-analysis of the
                   Weedman 1985 spectra in combination with NBCKDE
                   photometric redshifts for those objects.
     4.3  11Jan15  Quasar data brought up to publications as at 10 January
                   2015, including the newly-released SDSS-DR12 and
                   SDSS-DR12Q ( Approximately, 800 quasars
                   sourced from the AGES catalog, Kochanek et al. (2012,
                   ApJS, 200, 8). Approximately, 200 extra quasars added in a
                   full round-up from NED and SIMBAD.
     4.4  06Feb15  Quasar data brought up to publications as at 25 January
                   2015. Some reprocessing of the SDSS-DR12 and SDSS-DR12Q
                   data. About 1000 type-1 objects reclassified to type-2.
                   Photometric candidate likelihoods and redshifts were
                   recalibrated using the SDSS-DR12Q quasars as the benchmark.
     4.5  10May15  780 new quasars from LAMOST-DR1 (Luo et al. 2015,
                   arXiv:1505.01570) were added. LAMOST-DR1 is a pipeline
                   catalog with much provisional data, so the author selected
                   the best-eligible objects only. LAMOST plans a manual
                   (reliable) QSO catalog later this year. Also, NED/SIMBAD
                   quasar data is included up to 9 May 2015. Citations were
                   greatly simplified, referencing the recently published
                   Half Million Quasars catalog (HMQ: Flesch E., 2015
                   PASA, 32, 10, arXiv:1502.06303) for smaller legacy citations
                   while still citing large surveys like SDSS and 2QZ. A
                   legend for the citations is given below, and the separate
                   citations file is no longer needed as a result of this.
                   3XMM-DR5 (Rosen et al., 2015, arXiv:1504.07051) included
                   in X-ray data. Also, high-confidence data from 2XMMi-DR3
                   is included, as acknowledged in section 8.2 of the Rosen
                   paper (dropped 2XMMi-DR3 data recognized as valid). Minor
                   fixes to optical data resulted in a few more radio/X-ray
     4.6  30Nov15  Additional QSO candidates were sourced from the new
                   NBCKDE v3 catalog (Richards G.T. et al., 2015-ApJS-219-39)
                   and a variability and refraction sourced catalog (Peters
                   C.M. et al., 2015-ApJ-811-95). These added about 300,000
                   new candidates to Milliquas. Note that the NBCKDE v3
                   catalog uses different selection criteria from its
                   predecessor, and so augments it rather than superseding
                   it. The threshold for inclusion of QSO candidates was
                   raised from 80% QSO-likelihood to 90%, so the catalog
                   should be reliable even for spot checks. NED and SIMBAD
                   listed quasars were included through 30-Nov-2015.
     4.7  02Mar16  527 new QSOs were added from recent publications, including
                   33 new QSOs with z>5 of which 4 have z>6. The UV-Bright
                   Quasar Survey (UVQS, T.R. Monroe et al., arXiv:1602.06255)
                   was included with two mag-14 and 43 mag-15 QSOs plus many
                   brighter AGN.
     4.8  22Jun16  The Chandra ACIS source catalog (Wang S. et al., 2016,ApJS,
                   224,40) was added and new X-ray associations calculated.
                   The 2nd RASS source catalog 2RXS (Boller Th. et al., 2016,
                   A&A,588,103) replaced 1RXS for the most part, with
                   significant differences in places. Radio/X-ray processing
                   was tightened and data recalibrated to improve likelihood
                   reliability, as part of a new radio/X-ray catalog in
                   preparation. 23,727 radio/X-ray associated objects, recently
                   dropped, were restored on the criterion that they are each
                   80%+ likely to be true quasars. This was done because this
                   information is not found elsewhere.
     4.8b 30Jul16  The 3XMM-DR6 X-ray source catalog was added and new X-ray
                   associations calculated. The radio/X-ray data have been
                   reprocessed in line with that of the Million Optical
                   Radio/X-ray (MORX) Associations Catalog (Flesch 2016,
                   PASA, 33, 52).
     5.0  19Jun17  The J2000 coordinates now have 1/10th arcsecond precision,
                   and the magnitudes have 1/100th mag precision, either from
                   the original surveys or from the All-Sky Portable (ASP)
                   optical catalog (arXiv:1705.05434). 5414 net QSOs/AGNs were
                   added from recent surveys (listed below), notably AAOz,
                   OzDES, LAMOST DR2, and a reload of AGES. The 3XMM-DR7 and
                   XMMSL2-2.0 Slew X-ray source catalogs were added and new
                   X-ray associations calculated. A few duplicates were
                   removed. Notably, SDSS J131715.46+601533.1 was found to be
                   a duplicate of SBS 1315+605.
     5.1  30Jun17  Included full coverage of the Subaru-XMM Deep Field from
                   multiple authors, LAMOST DR3, and other miscellaneous
     5.2  05Aug17  SDSS-DR14 and SDSS-DR14Q were added, using the processing
                   rules from the Half Million Quasars catalog (HMQ: Flesch
                   2015, PASA, 32, 10). WISE quasar candidates were added
                   from Secrest et al. 2015, ApJS, 221, 12. These are
                   ~430,000 candidates over the whole sky for which 2-color
                   optical objects were found within a 2-arcsec radius. They
                   were processed into pQSOs from calibration against the
                   SDSS-DR12Q multi-class superset, and photometric redshifts
                   obtained using the four-color based method from the HMQ
                   Appendix 2. The four colors used were B-R, R-W1, W1-W2,
                   and W2-W3. Type-II narrow emission-line galaxies (NELGs,
                   class='N') were added as the luminosity class
                   corresponding to the type-I AGN galaxies. High-luminosity
                   type-II NLAGN (class='K') correspond to the type-I
                   quasars. The NLAGN/NELG divider is the same luminosity/psf
                   function which separates QSOs from AGNs. Type-II NELGs
                   include unquantified contamination by LINERs and probably
                   a few starbursts which eluded removal, so it serves as a
                   catch-all category presented for completeness, rather than
                   as a strict type-II class. Small publications through 5
                   August 2017 were added. Positional fixes (of about 2
                   arcsec) were applied to ~150 objects.
     5.3  12Sep18  Radio/X-ray association likelihoods calculated to a
                   granularity of 1/10th of an arcsecond for Chandra,
                   XMM-Newton, and Swift X-ray source catalogs and the FIRST
                   radio source catalog. All associations have been
                   recalculated onto the APM/USNO-B optical background of
                   Flesch 2017,PASA,34,25 (Figure 3). Radio/X-ray association
                   likelihoods to faint SDSS sources not in the optical
                   background were previously halved, based on the
                   approximately doubled sky density of SDSS. This deduction
                   was changed to be classed by PSF and red-blue color,
                   consequentially most SDSS likelihoods were reduced more,
                   often by 60%-90%. Associations to other faint objects were
                   also reduced. The overall effect was that ~20,000
                   candidates fell below the 80% likelihood threshold for
                   inclusion in Milliquas, and so were removed. Visually
                   inspected quasars from the LAMOST DR3Q (Dong et al.,
                   2018,AJ,155,189) and auto-quasars from the LAMOST DR4
                   ( were quality checked and a total
                   of 10,624 quasars/AGN added to Milliquas.
     5.4 17Oct18   Quasars from individual papers from August 2017 forward to
                   15 October 2018 have been added, plus some from a couple
                   older papers. Quasar doublets are more carefully processed
                   to show 2 quasars instead of 1. A few gravitationally
                   lensed images are added as type='L', in addition to the
                   already-catalogued brightest one. These are added only
                   where the optical data shows them in order to account for
                   any radio/X-ray associations to them. The 3XMM-DR8 X-ray
                   source catalog has been added and new X-ray associations
                   calculated. A bug in v5.3 dropped radio/X-ray associations
                   to some high-z quasars was fixed.
     5.5  19Nov18  Quasars from publications to 14 November 2018 were added.
                   The SDSS data were reprocessed to ensure DR14 data is used
                   where available. Close quasar pairs and lens images
                   processing was completed. 631 "unknown class" (type=U)
                   objects (SDSS pipeline QSOs without subclass) were added.
                   There are not usually accepted into Milliquas but they had
                   probable radio/X-ray associations of p>80% which thus
                   qualify them for inclusion. The SDSS pipeline redshift for
                   these were included provisionally. The J2000 decimal
                   round-up was increased to avert truncation.
     5.6  17Dec18  Quasars from publications to 15 December 2018 were added.
                   The 3rd release of SDSS-DR14Q (v4.4) was incorporated,
                   adding ~300 quasars which had no astrometry in their
                   earlier releases. All SDSS data was reprocessed to get rid
                   of artifacts which had crept in. In preparation for LAMOST
                   DR5Q (Yao et al 2018,arXiv:1811.01570), the LAMOST DR4
                   auto-quasars were demoted to quasar-candidates. LAMOST
                   pipeline quasars were processed using the same rules as
                   with SDSS pipeline. Removed 223 objects from
                   Iovino/Clowes/Shaver,1996,A&AS,119,265 which had no quasar
                   profile nor radio/X-ray/WISE associations, leaving 917 in
                   Milliquas, resolving the cautionary note from
                   HMQ (2015,PASA,32,10) section 2.B.4 end.
     5.7  07Jan19  Quasars were added from publications to 7 January 2019,
                   including LAMOST QSO DR5. The logic was tightened up for
                   using SDSS SUBCLASS and ZWARNING fields to decide
                   classifications for SDSS objects, including pipeline-only
                   candidates. Milliquas was previously classifying all
                   QSOs/AGN of z<0.1 as AGN. This boundary was moved to
                   z=0.05 because of many core-dominated QSOs between z=0.05
                   and 0.1, e.g., IRAS 01267-2157 (SDSS J012910.99-214156.8)
                   at z=0.93. HMQ (2015,PASA,32,10), section 5, discusses
                   these luminosity-based boundaries. 22 objects from Boyle
                   et al., 1990,MNRAS,243,18, classified by them as "possible"
                   QSOs with "uncertain" redshifts, were removed from
                   Milliquas. Positional fixes were done on ~90 legacy
                   objects, mostly moves of <5 arcsec.
     6.0  15Mar19  Quasars were added from publications to 15 March 2019.
                   For ease of use, the "HMQ" citation (necessitating
                   consultation of the HMQ catalog 2015-PASA-32-10 to
                   identify the discovery article) was replaced by the
                   HMQ-given 4-digit citation number. 30512 entries were
                   changed, and the HMQ references file can be directly
                   consulted for any numeric citation, making Milliquas into
                   a stand-alone catalog. Positional fixes were made to 9
                   legacy objects. Where SDSS had a different redshift for a
                   LAMOST-discovered quasar, if the difference is >0.1z, the
                   name and discovery credit were transferred to SDSS. This
                   was done for 6 objects. 42 AGN are dropped because their
                   discovery paper Mauch & Sadler 2007,MNRAS,375,931 flagged
                   those classifications as "not certain" and they had
                   neither stellar psfs nor secure (80%+) radio/X-ray
                   associations. The unseen Soviet BAL quasar "SBS 1401+566"
                   was dropped. The quasar "Q 1409+732" was moved to the
                   coordinates stated by its discovery paper Anderson &
                   Margon 1987,Nature,327,125, where a suitable object
                   resides. Confusion came from that paper's discrepant
                   finding chart onto a plate flaw.
     6.1  12May19  Quasars were added from publications to 12 May 2019.
                   Gaia-DR2 astrometry was used and flagged for 63% of
                   Milliquas (MQ) objects. Gaia sources were matched 1-to-1
                   with MQ objects on the criterion that the Gaia source is
                   that nearest to the MQ object and that the MQ object is
                   that nearest optical (out of a 1.163G optical DB) to the
                   Gaia source. Care was taken to avoid false matches. 99%
                   of all matches are within an arcsec offset, but to find
                   valid farther matches, all matches were binned by object
                   class and offset distance in 0.1 arcsec bins, with
                   hundreds of targeted spot checks done to refine offset
                   limits and to check objects with anomalous Gaia BP-RP
                   color suggestive of a false match. SDSS quasar candidates
                   could not be matched beyond 1 arcsec offset because they
                   are often optically faint and/or in close groups for which
                   Gaia had a different object only. AGN cores match to 1.5
                   arcsec beyond which Gaia often shows nearby stars only.
                   QSOs/Bl-Lacs match well out to within 4 arcsec; for these
                   I spot-checked all matches beyond 2 arcsec and all with
                   off-colors beyond 1 arcsec offset and removed 14 false
                   matches. However, for Gaia sources without BP and RP
                   colors, QSOs match reliably only within 2 arcsec and
                   Bl-Lacs within 1.5 arcsec. X-ray/radio-only candidates
                   (unique to MQ) match reliably out to within 2.5 arcsec
                   offset. In all cases it was paramount to avoid false
                   matches, thus very many true matches were lost beyond
                   the offset cutoffs. Reclassifications were done for
                   Milliquas objects deemed by the SDSS-DR14 pipeline to be
                   plain galaxies -- these were heavily spot-checked to
                   confirm. 16 QSOs, 172 AGN and 2343 type-II objects were
                   found to be just galaxies and so are dropped, and 433
                   host-dominated QSOs were reclassified to AGN.
     6.2  22May19  About 50 fixes were done on Gaia-DR2 opticals selected in
                   crowded places. Quasars were added from publications to 22
                   May 2019, including the PS-ELQS. 3LAC was reprocessed to
                   fix a few selections and improve completeness. The z=2.136
                   QSO "SDSS J101012.77+560520.0", overlooked by SDSS, was
     6.3  16Jun19  Quasars were added from publications to 15 June 2019,
                   including 4LAC. 3,581 galaxies with double radio lobes
                   were added as type=G because the lobes show that they have
                   active nuclei of some kind, even if well hidden.
                   Positional fixes of a few arcsec were done for ~50 legacy
                   objects. Blazar candidates with neither redshift nor
                   radio/X-ray association, about 30 objects, were dropped.
                   Most were stated to be low confidence in legacy papers.
     6.4  11Dec19  Quasars were added from publications to 11 December 2019.
                   The SDSS-DR16 pipeline release was added. The author
                   processed it using the standard HMQ rules which yield QSO
                   classifications that accord well to the follow-up manual
                   SDSS classifications. A new rule for Milliquas
                   classification was added such that STARFORMING and
                   STARBURST subclasses, or GALAXY classification by the
                   DR12Q superset, are now taken to indicate optical host
                   domination, e.g., classed as AGN instead of QSO. More
                   candidates with double radio lobes were added, active
                   nuclei being indicated. A photometric threshold guards
                   against starforming interlopers. The pQSOs of SDSS
                   candidates which are eBOSS targets were lowered due to
                   anti-selection, i.e., possibly DR16Q-classified as a
                   non-quasar. Candidates which consequently fell below
                   pQSO=80% (~57K) were dropped. The Chandra Source Catalog
                   v2 was added, but only as a supplement to the CSC v1.1
                   because v2 provides only stacked data for which the
                   optical solution used by Milliquas cannot be calculated.
     6.4b 19Dec19  Some extra processing of the new SDSS-DR16 data yielded 534
                   more type-I objects and fixed the astrometry of 381
                   objects which had been offset by up to 3 arcseconds. About
                   800 QSOs were flagged as host-dominated and so were
                   reclassified to AGN.
     6.4c 31Dec19  Quasars were added from publications to 31 December 2019.
                   The 4XMM-DR9 XMM-Newton catalog was added and X-ray
                   associations calculated, replacing 3XMM-DR8. The 2SXPS
                   Swift XRT catalog was added and X-ray associations
                   calculated, replacing 1SXPS. Gaia astrometry was removed
                   from 18 quasars and 66 candidates which were in doublets
                   (on the sky) for which Gaia had astrometry only for the
                   other object. SDSS-DR16 redshifts more fully replaced
                   earlier SDSS pipeline data.
     6.5  14Jun20  Quasars were added from publications to 14 June 2020.
                   Gaia-sourced parallaxes and proper motions were analyzed
                   to see if they could identify false quasars. Legacy quasar
                   publications were then group tested such that those with a
                   high flag rate (>20% compared with 2% overall, signaling
                   the presence of low-quality data) had their flagged
                   objects dropped, provided, as a confirmation, that those
                   objects also had no radio/X-ray associations. The counts
                   of dropped objects were:
                     -- 28 out of 40 (70%) from Zhan & Chen, 1987 & 1989 ChA&A
                     -- 400 out of 916 (44%) from Iovino/Clowes/Shaver,
                     -- 50 out of 194 (26%) from Savage/Trew/Chen/Weston,
                     -- 111 out of 517 (21%) from Drinkwater 1987.
                   In total, 589 "quasars" were dropped for having
                   parallaxes/proper motions. 136 SDSS-DR14 objects which
                   were dropped by SDSS-DR16 were removed. About 1500 objects
                   had their photometry supplemented from Pan-STARRS data.
     6.6  30Aug20  Quasars were added from publications to 30 August 2020.
                   The SDSS-DR16Q data (Lyke+ 2020) were incorporated.
                   Combined with the DR16 pipeline data, these contributed
                   ~200K new quasars beyond DR14 plus many valuable
                   reclassifications of the SDSS-IV data. In processing this
                   vast data pool, the author identified 37 new quasars not
                   classified by DR16/DR16Q. These were added in Milliquas
                   with ref_name="MQ" and ref_redshift="DR16QN"/"DR16". Data
                   selection of DR16 pipeline data was by HMQ (Flesch 2015)
                   rules, including choice of spectra. Data flagged with
                   ZWARNING=256 (bad astrometry) were validated by testing
                   and are included. Details of usage of the SDSS-DR16/DR16Q
                   data will be included in a Milliquas paper in preparation
                   (Flesch 2021).
     7.0  30Sep20  Quasars were added from publications to 30 September 2020.
                   SDSS-DR16 represented the conclusion of the eBOSS and BOSS
                   quasar surveys, and that conclusion somewhat orphaned the
                   leftover candidates from the SDSS-based photometric
                   catalogs. Said candidates without any radio/X-ray/WISE
                   associations were unlikely to be targeted in this decade,
                   and so were dropped from Milliquas, 574,538 of them. Said
                   candidates which did have WISE associations, numbering
                   35,086, were changed to display AllWISE names. These
                   significant changes prompted this release to be numbered
                   v7.0.Clean-ups were done on the uptake of SDSS-DR16Q/DR16
                   by Milliquas v6.6, notably 4,506 DR16Q quasars previous
                   presented as candidates, were designated to be QSOs. Also,
                   404 low-quality pipeline objects which were presented as
                   QSOs were dropped. WISEA photometric redshifts were
                   recalculated using the DR16-augmented training set, and
                   Pan-STARRS-based photometric redshifts were calculated for
                   radio/X-ray associated candidates on the PS1 footprint
                   (all-sky N of decl. S30) using the four-color method of
                   2015,PASA,32,10, Appendix 2. 222 candidates in a solid
                   degree centered on J2033+412 in Cygnus were dropped. They
                   are obvious stars, albeit near to background Galactic
                   X-ray sources.
     7.1  14Feb21  Quasars were added from publications to 14 February 2021.
                   For quasar candidates, the pQSO (likelihood that the
                   candidate is a quasar) threshold for inclusion into
                   Milliquas was lowered to 60%. This was done to present
                   more radio/X-ray associated candidates which were not
                   available elsewhere. Audits on the inclusion of DR16Q into
                   Milliquas led to tweaks of the selection of DR16Q objects.
                   Other SDSS data were also audited. Also, all galaxy data
                   are removed in order to focus exclusively on quasars.
                   LAMOST-DR6 was added -- being pipeline-only data, its
                   quasar classifications were accepted into Milliquas only
                   when supported by radio/X-ray/WISEA pQSOs. 4XMM-DR10 X-ray
                   sources were added, replacing DR9.
     7.2  02May21  See list of changes above.


The designation of the source as taken from the literature. Nameless radio/X-ray associated objects here utilize the J2000 position in "HHMMSS.SS+DDMMSS.S" for the convenience of the user. If needing a name for it, just prefix this value with "MQ ", e.g., MQ J000001.89+443053.8.

The Right Ascension of the quasar candidate in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-7 degrees in the original table. That suits objects with Gaia-DR2 astrometry and accommodates a minuscule round-up to avoid truncation in use, but it is too precise for other objects, although it prevents inadvertent truncation when converting to sexagesimal.

The Declination of the quasar candidate in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-7 degrees in the original table. That suits objects with Gaia-DR2 astrometry and accommodates a minuscule round-up to avoid truncation in use, but it is too precise for other objects, although it prevents inadvertent truncation when converting to sexagesimal.

The Galactic Longitude of the quasar candidate. This parameter has been added by the HEASARC and is converted from the provided equatorial position.

The Galactic Latitude of the quasar candidate. This parameter has been added by the HEASARC and is converted from the provided equatorial position.

The classification of the object, where the following abbreviations are used:

       Q = QSO, type-I broad-line core-dominated, 790776 of these.
       A = AGN, type-I Seyferts/host-dominated, 38890 of these.
       B = BL Lac object, 2704 of these.
       L = lensed quasar extra image, only 64 of these in this optical data.
       K = NLQSO, type-II narrow-line core-dominated, 5316 of these.
       N = NLAGN, type-II Seyferts/host-dominated, 32726 of these.  Includes an
                  unquantified residue of legacy NELGs/ELGs/LINERs.
       q = quasar candidate of the displayed QSO likelihood, 559424 of these.
       R = radio association displayed.
       X = X-ray association displayed.
       2 = double radio lobes displayed (declared by data-driven algorithm).

The red optical magnitude of the object. The type and source of this magnitude is specified in the optical_flag parameter value. Optical data are mostly from the ASP optical catalog (2017,PASA,34,25) which presents data from the APM (, USNO-A and USNO-B (, and the SDSS ( APM/USNO-A magnitudes were recalibrated from the original values as documented in 2004,A&A,427,387. As a result, these recalibrated USNO-A magnitudes are often used in preference to USNO-B. APM galaxies brighter than 17th magnitude are usually represented as far too bright due to PSF modeling. Integer magnitudes (e.g., 22.00) are estimates if both bands are integers or one band is empty. If the optical_flag parameter value contains r/b/g/i/v/u/z, then the magnitudes are from the object's source catalog, e.g., SDSS, 2QZ, etc. Note that many SDSS magnitudes are extinction-"corrected" ~0.3 mag brighter than observed.

The blue optical magnitude of the object. The type and source of this magnitude is specified in the optical_flag parameter value. Optical data are mostly from the ASP optical catalog (2017,PASA,34,25) which presents data from the APM (, USNO-A and USNO-B (, and the SDSS ( APM/USNO-A magnitudes were recalibrated from the original values as documented in 2004,A&A,427,387). As a result, these calibrated USNO-A magnitudes are often used in preference to USNO-B. APM galaxies brighter than 17th magnitude are usually represented as far too bright due to PSF modeling. Integer magnitudes (e.g., 22.00) can be estimates if both bands are integer or one band empty. If the optical_flag parameter value contains r/b/g/i/v/u/z, then the magnitudes are from the object's source catalog, e.g., SDSS, 2QZ, etc. Note that many SDSS magnitudes are extinction-"corrected" ~0.3 mag brighter than photometry.

This field contains coded information on the optical source properties, as follows:

       p = optical magnitudes are POSS-I O (violet 4050A) and E (red 6400A).
           These are preferred because O is well-offset from E, and those plates
           were always taken on the same night, thus the red-blue color is
           correct even for variable objects. The epochs for these are 1950s.
       j = optical magnitudes are SERC J (Bj 4850A) and R (red 6400A) from the
           POSS-II or UKST surveys.  Red-blue color is less reliable because the
           red and blue plates were taken in different epochs, i.e., years apart.
       b = blue magnitude is Vega 4400A (Johnson), red is 6400A (Cousins).
       g = blue magnitude is SDSS-type green 4900A, red is r 6200A.
       u = blue magnitude is SDSS ultraviolet 3850A.
       v = red magnitude is visual, i.e., white, 5500A midpoint.
       i = red magnitude is infrared 7500A.
       z = red magnitude is infrared z 8600A.
       r = red magnitude is r 6200A.
       (blank) =  Pan-STARRS r 6200A & g 4900A, but red alone is 6400A (Cousins).
       G = Gaia-DR2 astrometry shown, precessed to J2000 by CDS.  If 'G' is alone
           then the magnitudes are Gaia RP & BP, or Gaia G if red band only.
       + = variability nominally detected in both red/blue over multi-epoch data.
       m = proper motion nominally detected, from USNO-B.
       % = swap of two "unplugged" SDSS spectra which crossed wires (7 of these).
       a = object is host-dominated with faint nuclear activity, such as an SDSS
           pipeline galaxy with an AGN subclass or AGN-classed elsewhere, see
           its citation.  Milliquas class is 'A' if BROADLINE, else 'N'. (See

A coded representation for the point spread function (PSF) of the optical source in the red. The APM, USNO-B, and SDSS provide PSF class, albeit using different criteria. The codes are as follows:

       - = point source / stellar PSF (APM notation: -1, here truncated)
       1 = fuzzy / galaxy shape       (APM notation: 1 and some 2)
       n = no PSF available, whether borderline or too faint to tell, etc.
       x = not seen or unclear in this band (although may show a Pan-STARRS

A coded representation for the point spread function (PSF) of the optical source in the blue. The APM, USNO-B, and SDSS provide PSF class, albeit using different criteria. The codes are as follows:

       - = point source / stellar PSF (APM notation: -1, here truncated)
       1 = fuzzy / galaxy shape       (APM notation: 1 and some 2)
       n = no PSF available, whether borderline or too faint to tell, etc.
       x = not seen in this color (fainter than plate depth, or confused, etc.)

The redshift of the object, taken from the literature as specified in the ref_redshift parameter. Spectroscopic/grism redshifts are required for objects classified as Q/A/K/N/L and is optional for B (BL Lac type). Photometric redshifts rounded to 0.1z can be displayed for q/B/R/X/2 objects, and are either taken from the cited catalog or calculated here using the four-color method of Flesch 2015,PASA,32,10, Appendix 2, using 4 colors from SDSS ugriz, Pan-STARRS grizy or orgriz with calibrated POSS-I O, or, for WISEA, the 4 colors B-R, R-W1, W1-W2, and W2-W3.

A character code for the literature reference from which the name was taken is indicated below. The meaning of any 4-digit numerical code can be found in the references list of the author's Half Million Quasars Catalog (HMQ: Flesch 2015, PASA, 32, 10) at

       Code (No. of names, No. of redshifts): Reference

       2dF (357,211): 2dF galaxy survey, Colless M. et al., 2001,MNRAS,328,1039
       2QZ (27520,24157): Croom S.M. et al., 2004,MNRAS,349,1397
       2SLAQ (10353,8679): Croom S.M. et al., 2009,MNRAS,392,19
       3FGL (16,11): Fermi cleanups, Paiano S. et al., 2017,ApJ,851,135
       3FGL2 (21,19): Fermi cleanups II, Paiano S. et al., 2019,ApJ,871,162
       3HSP (819,999): 3HSP blazars, Chang Y.-L. et al., 2019,A&A,632A,77
       3XLSS (25,25): The XXL Survey, Pierre M. et al., 2016,A&A,592A,1P
       4FGL1 (15,3): Fermi cleanups, de Menezes R. et al., 2019,A&A,630A,55
       4FGL2 (18,22): Fermi cleanups X, de Menezes R. et al., 2020,Ap&SS,365,12
       4LAC (367,349): Fermi AGN v4 + LL, Fermi-LAT collab., 2020,ApJ,892,105
       6dF (315,223): 6dF galaxy survey, Jones D.H. et al., 2009,MNRAS 399,683
       AAOz (1491,1498): AAOmega XXL-South: Lidman C. et al., 2016,PASA,33,1
       AGES (2046,2046): AGES survey, Kochanek C.S. et al., 2012,ApJS,200,8
       AGNELL (2,3): DES lenses, Agnello A. et al., 2015,MNRAS,454,1260
       AGNELA (4,4): SDSS J1433+6007 4-lens, Agnello A. et al., 2018,MNRAS,474,3391
       AGNEL2 (13,13): VST-Gaia QSO pairs, Agnello A. et al., 2018,MNRAS,475,2086
       AKARI (1,1): overlooked luminous quasar, Aoki K. et al., 2011,PASJ,63,457
       ALMA (4,4): ALMA hi-z, Roberto Decarli R. et al., 2018,ApJ,854,97
       ANDIKA (2,2): Hi-z starbursts: Andika I.T. et al., 2020,ApJ,903,34
       ANGUIT (1,1): COSMOS lens, Anguita T. et al., 2009,A&A,507,35
       ATel (5,5): Astronomers Telegraph posts,
       ATHENS (86,108): VIPERS AGN SEDs, Pouliasis E. et al., 2020,MNRAS,495,1853
       ATLAS (229,269): Mao M.Y. et al., 2012,MNRAS,426,3334
       BAHM (24,24): dust-reddened QSOs, Banerji M. et al., 2015,MNRAS,447,3368
       BASS (16,113): Swift-BAT AGN, Koss M. et al., 2017,ApJ,850,74
       BERGHE (1,1): Pan-STARRS lens, Berghea C.T. et al., 2017,ApJ,844,90
       BGGFC (4,4): COSMOS hi-z, Boutsia K. et al., 2018,ApJ,869,20
       BLAZZ (0,8): Blazar redshifts, Goldini P. et al., 2020,arXiv:2012.05176
       BMCGCS (1,1): Belladitta S. et al., 2019,A&A,629A,68
       BMCS (1,1): Blazar at z>6, Belladitta S. et al., 2020,A&A,635L,7
       BQLS (16,16): BOSS QSO lenses & pairs, More A. et al., 2016,MNRAS,456,1595
       BZCAT (4,3): Blazars catalog, Massaro E. et al.,
       C-COSM (180,180): Chandra COSMOS IDs, Marchesi S. et al., 2016,ApJ,817,34
       ChaMP (191,187): Trichas M. et al., 2012,ApJS,200,17
       DABAST (1,1): Diaz-Santos T. et al., 2018,Sci,362,1034
       Dart (26,25): Heavily Obscured QSOs, Hviding R. et al., 2018,MNRAS,474,1955
       DDC2 (14,14): variable AGN, De Cicco D. et al., 2019,A&A,627A,33
       DEEP (143,139): DEEP2, Newman J. et al., 2013,ApJS,208,5;
       DES (1,1): Dark Energy hi-z, Reed S.L. et al., 2015,MNRAS,454,3952
       DESQQ (26,26): STRIDES lenses, Anguita T. et al., 2018,MNRAS,480,5017
       DESQQ2 (12,12): STRIDES lenses, Treu T. et al., 2018,MNRAS,481,1041
       DPeake (683,656): Double-peaked NELGs, Ge J.-Q. et al., 2012,ApJS,201,31
       DR12 (6,6): Alam S. et al., 2015,ApJS,219,12,
       DR12Q (244,15): SDSS-DR12Q, Paris I. et al., 2017,A&A,597,79
       DR14 (12,44): Abolfathi B. et al., 2018,ApJS,235,42, pipeline,
             data at
       DR14Q (1527,1538): SDSS-DR14Q, Paris I. et al., 2018,A&A,613A,51,
             data at
       DR16 (41065,374519): Ahumada R. et al., 2020,ApJS,249,3, pipeline,
             data at
       DR16Q (715827,395233): SDSS-DR16Q, Lyke B. et al., 2020,ApJS,250,8
             2 files, data at
       DR16QN (0,2132): same as above, using the QuasarNET redshift supplied.
       DR7 (2,26): SDSS DR7, Abazajian K.N. et al., 2009,ApJS,182,543,
             files at
       DR7Q (1967,200): SDSS Quasar DR7, Schneider D. et al., 2010,AJ,139,2360
       DUALQ (1,1): Dual QSOs HSC, Silverman J.D. et al., 2020,ApJ,899,154
       DUHIZ (2,2): DECaLS-UKIRT hi-z, Wang F. et al., 2017,ApJ,839,27
       Dusty (11,11): Dusty Starbursts, Rodighiero G. et al., 2019,ApJ,877,38
       DUz6 (18,18): DESI & UKIRT hi-z, Wang F. et al., 2019,ApJ,884,30
       eHAQ (82,80): Extended High AV, Krogager J.-K., 2016,ApJ,832,49
       ELQ-PS (216,215): ELQS on PS1, Schindler J.-T. et al., 2019,ApJS,243,5
       ELQS-N (38,38): ELQS in NGC, Schindler J.-T. et al., 2018,ApJ,863,144
       ELQS-S (126,126): ELQS in SGC, Schindler J.-T. et al., 2019,ApJ,871,258
       FISCBA (1,1): HST lens, Fischer/Schade/Barrientos, 1998,ApJ,503,L127
       FLES40 (40,0): Salvaged QSOs, Flesch E.W., 2021,MNRAS,504,621
       FYNBO (1,1): LiBAL QSO, Fynbo J.P.U. et al., 2020,A&A,634A,111
       GAIA1 (21,21): Gaia DR1, Gaia Collaboration et al., 2016,A&A,595A,1
       GAIA2 (236,232): Gaia DR2, Gaia Collaboration et al., 2018,A&A,616A,1,
             (GAIA data as presented by SIMBAD,
       GEIER (1,1): Geier S.J. et al., 2019,A&A,625L,9
       GGLS (3,4): Gaia GraL, Krone-Martins A. et al., 2019,arXiv:1912.08977
       GLDD (1,1): Lensed QSO data-driven, Ostrovski F. et al., 2017,MNRAS,465,4325
       GLIKMA (28,28): red WISE QSOs, Glikman E. et al., 2018,ApJ,861,37
       GLOH (1,1): Grav Lensed Objs HSC, Jaelani A.T. et al., 2021,MNRAS,502,1487
       GLRED (1,1): lensed red QSO, Glikman E. et al., 2018,arXiv:1807.05434
       GQ (2,2): serendipitous binary, Altamura E. et al., 2020,AJ,159,122
       GRAL4 (10,10): Gaia Grav Lens quads, Stern D. et al., 2020,arXiv:2012.10051
       GUTI (1,1): not a ULX, Gutiérrez C.M., 2013,A&A,549,A81
       GZPM (23,23): Gaia zero pm, Heintz K.E. et al., 2020,A&A,644A,17
       H-DOGs (16,16): Herschel DOGs, Riguccini L.A. et al., 2019,A&A,625,9
       HAQ (2,2): High AV serendipitous, Heintz K.E. et al., 2016,AJ,152,13
       HAQC (1,1): High AV in COSMOS, Heintz K.E. et al., 2016,A&A,595,13
       HE2QS (103,103): HeII quasar survey, Schmidt T.M. et al., 2017,ApJ,847,81
       HE2QS2 (5,5): HeII HST/COS quasars, Worseck G. et al., 2019,ApJ,875,111
       HEINTZ (1,1): dusty absorbed QSO, Heintz K.E. et al., 2018,A&A,615A,43
       HIZ7.5 (1,1): QSO z=7.5, Bañados E. et al., 2018,Natur,553,473
       HSC (3,3): Low-luminosity QSOs, Niida M. et al., 2020,ApJ,904,89
       HSTvar (42,42): variable AGN, Pouliasis E. et al., 2019,MNRAS,487,4285
       ICECUB (9,12): IceCube spectra, Paiano S. et al., 2021,MNRAS,504,3338
       IGMCP (10,10): IGM close pairs, Rorai A. et al., 2017,Sci,356,418
       IKEDA (1,1): Ikeda H. et al., 2017,ApJ,846,57
       IMDS (3,3): IR medium-deep hi-z VII, Shin S. et al., 2020,ApJ,893,45
       IMS (1,1): IR medium-deep hi-z, Kim Y. et al., 2015,ApJ,813,35
       IMS2 (10,11): IR medium-deep hi-z, Kim Y. et al., 2019,ApJ,870,86
       INAF (1,1): UV bright hi-z, Grazian A. et al., 2020,ApJ,897,94
       JERAM (1,1): extremely bright, Jeram S. et al., 2020,ApJ,899,76
       JPLUS (24,24): luminous Ly, Spinoso D. et al., 2020,A&A,643A,149
       K4K (2,2): K4000 bz, Uwitonze/Nkundabakura/Mutabazi, 2020,arXiv:2004.03154
       KHOR1 (7,6): 3XMM hi-z, Khorunzhev G.A. et al., 2017,AstL,43,135
       KHOR2 (11,11): 3XMM hi-z, Khorunzhev G.A. et al., 2019,AstL,45,411
       KHOR3 (1,1): X-ray luminous, Khorunzhev G.A. et al., 2021,arXiv:2104.05142
       KODQ3 (4,4): KODIAQ DR3, O'Meara J.M. et al., 2021,AJ,161,45
       KOVACS (1,1): bright QSO behind Milky Way, Kovács T. et al., 2019,RNAAS,3,3
       LAMDR6 (2966,3341): LAMOST-DR6, pipeline,
       LAMQ1 (684,625): LAMOST QUASAR DR1, Ai Y.L. et al., 2016,AJ,151,24
       LAMQ3 (6698,6587): LAMOST QUASAR DR3/DR2, Dong X.Y. et al., 2018,AJ,155,189
       LAMQ5 (7938,7937): LAMOST QUASAR DR5/DR4, Yao S. et al., 2019,ApJS,240,6
       LEMON (40,40): 24 Gaia lenses, Lemon C. et al., 2018,MNRAS,479,5060
       LEMON2 (30,30): 22 Gaia lenses, Lemon/Auger/McMahon, 2019,MNRAS,483,4242
       LEMON3 (53,52): STRIDES lenses etc, Lemon C. et al., 2020,MNRAS,494,3491
       LGGS (11,11): M31/M33 area, Massey/Neugent/Levesque, 2019,AJ,157,227
       LIDMAN (1,1): SN Host Galaxy redshifts, Lidman C. et al., 2013,PASA,30,1
       LIN (1,1): DES lens, Lin H. et al., 2017,ApJ,838,15
       LIRAS (169,154): LoCuSS IR AGNs, Xu, L. et al., 2015,ApJS,219,18
       LOZAGN (38,10997): Low-redshift AGN, Liu H.-Y. et al., 2019,ApJS,243,21
       LSSA (2,1): 2 lenses, Lucey/Schechter/Smith/Anguita, 2018,MNRAS,476,927
       LUMIz5 (66,66): Luminous hi-z, Yang J. et al., 2019,ApJ,871,199
       M31UV (1,1): UV flare QSO on M31, Meusinger H. et al., 2010,A&A,512,A1
       MALS-N (69,68): MEERKAT QSOs, Krogager J.-K. et al., 2018,ApJS,235,10
       MFJC (52,51): McGreer I.D., Fan X., Jiang L. & Cai Z., 2018,AJ,155,131
       MQ (143925,539324): MILLIQUAS, original data in this catalog, Flesch E.,2021
       NBCKDE (2559,2656): Richards G.T. et al., 2009,ApJS,180,67
       NBCKv3 (13224,67795): NBCKDE v3, Richards G.T. et al., 2015,ApJS,219,39
       NED (5,6): NASA/IPAC Extragalactic Database,
       OGLE2 (2,2): OGLE quasars, Kozlowski S. et al., 2019,ApJ,878,115
       OVRLAP (5,5): SDSS overlap hi-z QSOs, Jiang L. et al., 2015,AJ,149,188
       OzDES (608,435): Dark Energy SN QSOs, Tie S.S. et al., 2017,AJ,153,107
       OzDES2 (751,921): DESN QSOs, Lidman C. et al., 2020,MNRAS,496,19
       P352-1 (1,1): P352-15, Bañados E. et al., 2018,ApJ,861L,14
       PETERS (245,268): photo special, Peters C.M. et al., 2015,ApJ,811,95
       PFTS (2,11): blazar spectroscopy, Paiano S. et al., 2020,MNRAS,497,94
       PGC (12914,8): Principal Galaxy Catalog, Paturel G. et al., 2003,A&A,412,45
       PHILLI (1,0): MERLIN lens, Phillips P.M. et al., 2000,MNRAS,319,L7
       PS1 (63,63): PAN-STARRS1 hi-z, Bañados E. et al., 2016,ApJS,227,11
       PS1hiz (1,1): Tang, Ji-Jia et al., 2017,MNRAS,466,4568
       PS1MAZ (6,6): Mazzucchelli C. et al., 2017,ApJ,849,91
       PSO (3,3): PAN-STARRS z-dropouts, Venemans B.P. et al., 2015,ApJ,801L,11
       QLSV (21,20): QUEST-La Silla, Sánchez-Sáez P. et al., 2019,ApJS,242,10
       QPQ10 (70,70): Quasar pair DB, Findlay J.R. et al., 2018,ApJS,236,44
       QUBRIC (91,91): QUBRICS I, Calderone G. et al., 2019,ApJ,887,2
       QUBRIX (249,252): QUBRICS II, Boutsia K. et al., 2020,ApJS,250,26
       RBS (3,3): Laporte N. et al., 2017,ApJ,851,40
       Redden (25,25): Reddened QSOs, Temple M.J. et al., 2019,MNRAS,487,2594
       REQ4 (6,6): Reionization-Era quasars, Yang J. et al., 2019,AJ,157,236
       REQ7 (1,1): Reionization-Era QSO z=7.5,Yang J. et al., 2020,ApJ,897,14
       RLQ (4,3): Tuccillo D./Gonzalez-Serrano J.I./Benn C.R., 2015,MNRAS,449,2818
       RSG (1,1): Dorn-Wallenstein T.Z. & Levesque E., 2017,IAUS,329,376
       S82X (71,75): Stripe 82 AGN, LaMassa S.M. et al., 2019,ApJ,876,50
       S82XRQ (8,8): Red Quasars, LaMassa S.M. et al., 2017,ApJ,847,100
       SAGE1 (1,1): SAGE IR AGN, Hony S. et al., 2011,A&A,531A,137
       SCULPT (2,3): Sculptor X-ray, Arnason R. M. et al., 2019,MNRAS,485,2259
       SDLENS (3,3): SDSS Lenses, Williams P.R. et al., 2018,MNRAS,477L,70
       SDSSHI (6,6): SDSS hi-z, Jiang L. et al., 2016,ApJ,833,222
       SELMAN (1,1): serendipitous, Selman F.J. et al., 2020,AN,341,26
       SFM201 (1,1): Schulze S. et al., 2012,A&A,546,20
       SHELLQ (33,33): Subaru hi-z, Matsuoka Y. et al., 2018,PASJ,70S,35
       SHELQ3 (28,28): Subaru hi-z, Matsuoka Y. et al., 2019,ApJ,883,183
       SHELQS (30,30): SHELLQS hi-z, Matsuoka Y. et al., 2018,ApJS,237,5
       SHELz7 (1,1): SHELLQS z=7, Matsuoka Y. et al., 2019,ApJ,872L,2
       SMSSQ (2,2): SkyMapper hi-z, Zefeng Li Z. et al., 2018,arXiv:1805.03429
       SOLARZ (13,13): AllWISE anomalies, Solarz A. et al., 2020,A&A,642A,103
       SPIN18 (1,1): KiDS-SQuaD lens, Spiniello C. et al., 2018,MNRAS,480,1163
       SPIN19 (2,2): 2 lensed quasars, Spiniello C. et al., 2019,MNRAS,485,5086
       SQLS (60,51): SDSS DR7 QSO Lens Search, Inada N. et al., 2012,AJ,143,119
       SQUAD (13,13): UVES DB DR1, Murphy M.T. et al., 2019,MNRAS,482,3458
       SSLENS (3,3): South sky lenses, Spiniello C. et al., 2019,MNRAS,483,3888
       SUV (22,22): SDSS-ULAS/VHS QSOs, Yang J. et al., 2017,AJ,153,184
       SXDF (39,39): Subaru-XMMDF redshifts, Simpson C. et al., 2012,MNRAS,421,3060
       SXDS (307,306): Subaru-XMMDF spectra, Akiyama M. et al., 2015,PASJ,67,82
       ULTRA (1,1): Ultraluminous hi-z, Wu, X.-B. et al., 2015,Nature,518,512
       UVQS (435,503): UV QSOs, Monroe T.R. et al., 2016,AJ,152,25
       VAHIZ (2,2): VST ATLAS hi-z, Carnall A.C. et al., 2015,MNRAS,451,16
       VAHIZ2 (1,1): bright z>6 QSOs, Chehade B. et al., 2018,MNRAS,478,1649
       VAHIZ3 (1,1): VST-ATLAS lens, Schechter P.L. et al., 2018,RNAAS,2b,21
       VAQL (11,11): VST-ATLAS quasar systems,Schechter P.L. et al.,2017,AJ,153,219
       VDES (8,8): VISTA Dark Energy QSOs, Reed S.L. et al., 2017,MNRAS,468,4702
       VDES2 (2,2): more VHS-DES quasars, Reed S.L. et al., 2019,MNRAS,487,1874
       VIKING (4,4): VIKING IR, Venemans, G.A. et al., 2015,MNRAS,453,2259
       VIPERS (241,283): VIPERS PDR-2, Scodeggio M. et al., 2018,A&A,609A,84
       VMC (34,34): Magellanic IR QSOs, Ivanov V.D. et al., 2016,A&A,588,A93
       WARSAW (3,3): OGLE lens, Kostrzewa-Rutkowska Z. et al.,2018,MNRAS,476,663
       WERTZ (1,1): Gaia GraL lens, Wertz O. et al., 2019,A&A,628A,17
       WGD (2,2): DES/Gaia lenses; Agnello A. et al., 2018,MNRAS,479,4345
       WILLIG (1,1): Williger, G., 2020, p comm., data on LJMU Robotic Telescope
       WISEA (522905,0): AllWISE QSO candidates, Secrest N. et al.,2015,ApJS,221,12
       WISEHI (72,70): Hi-z QSOs from WISE, Wang F. et al., 2016,ApJ,819,24
       WOLF1 (1,0): most ultraluminous QSO, Wolf C. et al., 2018,PASA,35,24
       WOLF2 (16,16): hi-z ultraluminous QSOs, Wolf C. et al., 2020,MNRAS,491,1970
       WYFH (1,1): z=7.642 quasar, Wang F. et al., 2021,ApJ,907,1
       XDQSO (20119,0): SDSS-XDQSO, Bovy J. et al., 2011,ApJ,729,141
       XLSS (306,118): Stalin C.S. et al., 2010,MNRAS,401,294
       XMM2 (12,12): 2XMM-Newton cross-search, Combi J.A. et al., 2011,Ap&SS,331,53
       XMMSMC (6,6): SMC quasars, Maitral C. et al., 2019,A&A,622A,29
       XMSS (182,148): Barcons X. et al., 2007,A&A,476,1191
       XWAS (490,449): Esquej P. et al., 2013,A&A,557,123
       YQLF (25,25): deep CFHT QSOs, Yang J. et al., 2018,AJ,155,110
       YSZ (0,414): Type 2 QSOs IDd, Yuan/Strauss/Zakamska, 2016,MNRAS,462,1603
       z6.51 (1,1): lensed quasar z=6.51, Fan X. et al., 2019,ApJ,870L,11
       z6.82 (1,1): radio-loud z=6.82, Bañados E. et al., 2021,ApJ,909,80
       z7.02 (1,1): lensed quasar z=7.02, Wang F. et al., 2018,ApJ,869L,9
The citation for the classification (e.g., that the object is a quasar) can be from either the name or redshift citation. Four-digit numeric citations can be found in the HMQ (2015,PASA,32,10) references list.

A character code for the literature reference from which the redshift was taken, using the same rubric as used for the ref_name parameter (q.v.).

For a QSO candidate (type starting with q/R/X/2), this field contains its pQSO, the nominal probability that this object is a QSO, in percent, based on radio/X-ray association and/or photometric analysis. Radio/X-ray based likelihoods are calculated as described in Flesch & Hardcastle, 2004,A&A,427,387. WISEA photometric pQSOs are calibrated all-sky via the colors B-R, R-W1, W1-W2, and W2-W3, using the method of Flesch 2015,PASA,32,10, Appendix 2. SDSS-based candidates from NBCKDE/NBCKv3/XDQSO/Peters photometric catalogs can also have photometric-based pQSOs which are here calibrated against SDSS-DR16Q classified objects using 4-color matching.

The calibrated photometric pQSO (P1) and radio/X-ray derived pQSO (P2), if both are present, are combined into a single pQSO as

       P = 1/(1+((1-P1)*(1-P2))/(P1*P2)).
For a fully classified object (class starting with Q/A/B/K/N/L), this shows the percent chance that a shown radio/X-ray detection(s) is truly associated to it. If there is no radio/X-ray detection, the value is blank.

The identification of the radio source associated with the quasar candidate, if any.

This is usually the identification of the X-ray source associated with the quasar candidate, if any, but it can also be the identification of a radio lobe, if the radio_name parameter for the object itself contains the name of a radio lobe.

Radio/X-ray detections come from the following catalogs (and their respective home pages):

       FIRST: VLA FIRST survey, 13Jun05 version,
       VL0 (abbrev. for VLASS1QLCIR): VLASS Quick Look,
       NVSS: NRAO VLA sky survey,
       SUMSS: Sydney U. Molonglo,
       MGPS: Molonglo galactic plane,
       ROSAT catalogs available from are:
           - IX/28A is 1RXH: ROSAT HRI (high resolution imager)
           - IX/30 is 2RXP: ROSAT PSPC (position sensitive proportional counter)
           - IX/10A & IX/29 are 1RXS: ROSAT RASS (all-sky survey, bright & faint)
       2RXS: 2nd RASS source catalog,
       1WGA: White, Giommi & Angelini,
       CXOG: Chandra ACIS source catalog, Wang S. et al., 2016,ApJS,224,40
       CXO:  Chandra Source Catalog v1.1,
       2CXO: Chandra Source Catalog v2,
       CXOX: XAssist Chandra source list,
       2XMM/2XMMi: XMM-Newton DR3, IX/39&40
       4XMM: XMM-Newton DR10,
       XMMSL: XMM-Newton Slew Survey Release 2.0, same attribution as 4XMM
       XMMX: XAssist XMM-Newton source list,
       2SXPS: Swift X-ray Point Source Catalog,
Optical field solutions are calculated from the raw source positions of all these catalogs (except 2CXO) as described in the author's MORX paper (2016,PASA,33,52).

The identification of the radio lobe (as indicated by a "2" in the broad_type parameter) or an additional radio or X-ray identification associated with the quasar candidate, if any.

An additional identification of the radio lobe (as indicated by a "2" in the broad_type parameter) or an extra X-ray identification associated with the quasar candidate, if any.

The HEASARC Browse object classification, based on the information given in the broad_type parameter.

Contact Person

Questions regarding the MILLIQUAS database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 01-Jun-2021 13:33:25 EDT