[Paper Review] The Million Quasars (Milliquas) v7.2 Catalogue, now with VLASS associations. The inclusion of SDSS-DR16Q quasars is detailed

Eric Wim Flesch|arXiv (Cornell University)|May 27, 2021

Astrophysics and Cosmic PhenomenaPhysics and Astronomy38 citations

TL;DR

Milliquas v7.2 releases a catalog of all published quasars up to 30 April 2021, now including VLASS radio associations and a thorough audit of SDSS-DR16Q, with significant pruning for purity and extensive cross-matching with multiwavelength data.

ABSTRACT

Announcing the release v7.2 of the Milliquas (Million Quasars) catalogue which presents all published quasars to 30 April 2021, including VLASS radio associations for the first time, and concluding the audit of quasars from SDSS-DR16Q and earlier SDSS releases. The totals are 829666 classified type-I QSOs/AGN, 703348 quasar candidates of 60%-100% pQSO, plus type-II objects and blazars which bring the total count to 1573824. Radio and/or X-ray associations, including probable double radio lobes, are shown for 333638 entries. Gaia-DR2 astrometry is given for most objects, as available. The catalogue is available on multiple sites. The inclusion of the SDSS-DR16Q quasars was a complex task with emergent issues which resulted in 13443 DR16Q entries being dropped, 1.79% of their total. There are also 1701 quasars included from earlier visual SDSS releases, as well as 14232 quasars from the SDSS-DR16 pipeline catalogue. All these are explained here, including the validation of 677 additional high-redshift (z>=3.5) SDSS quasars which were not included in DR16Q.

Motivation & Objective

• Audit and consolidation of published quasars up to 30 April 2021 within Milliquas.
• Incorporate VLASS radio associations for the first time.
• Audit and refine SDSS-DR16Q and earlier SDSS releases to ensure high-purity quasar identifications.
• Explain inclusion/exclusion criteria and detection of low-purity subsets in DR16Q.
• Provide a transparent methodology for handling legacy and pipeline SDSS data in Milliquas.

Proposed method

• Aggregate quasars from published literature and SDSS-based catalogs following the HMQ framework.
• Apply purity-focused sifting rules using DR16Q flags (e.g., IS_QSO_FINAL, ZWARNING, Z_CONF) and SUBCLASS when available.
• Incorporate radio/X-ray/WISEA associations and Gaia-DR2 astrometry where applicable.
• Reconcile DR16Q with DR14Q/DR12Q/DR7Q contributions, dropping low-purity or dubious entries (e.g., 13 443 net DR16Q inputs dropped).
• Adopt QuasarNET redshifts selectively when they align better with spectra than pipeline redshifts (DR16 pipeline objects with ZWARNING=4).
• Flag high-redshift (z ≥ 3.5) quasars with visual confirmation and preserve hi-z identifications from DR14Q/DR12Q where appropriate.

Experimental results

Research questions

• RQ1 How many quasars and quasar candidates are included in Milliquas v7.2 after VLASS associations and DR16Q auditing?
• RQ2 What are the criteria and impact of excluding low-purity DR16Q entries on the Milliquas catalog?
• RQ3 How does Milliquas v7.2 integrate DR16Q hi-z quasars and DR14Q/DR12Q/DR7Q legacy objects?
• RQ4 What is the role of multiwavelength associations (radio/X-ray/AllWISE) and Gaia astrometry in validating quasar identifications?
• RQ5 How many new quasars and new quasar candidates were added or swapped due to DR16Q and pipeline revisions?

Key findings

• Milliquas v7.2 includes 829,666 type-I QSOs/AGN and 703,348 quasar candidates with pQSO 60%-100%, plus type-II objects and blazars for a total of 1,573,824 objects.
• Radio and/or X-ray associations are shown for 333,638 entries, including probable double radio lobes.
• SDSS-DR16Q entries were reduced by 13,443 (1.79% of DR16Q total) due to low-purity subsets and questionable classifications; 665 DR16Q IS_QSO_FINAL=2 objects were dropped.
• A total of 15,531 additional SDSS quasars not fully represented in DR16Q were included from DR16 Superset, DR14Q visual catalog, and DR12Q inheritance, with careful cross-checks (e.g., 677 hi-z quasars validated).
• Hi-z DR16Q entries accepted into Milliquas: 9,238 as hi-z quasars from DR16Q after exclusions; 7, diagonally, detailed breakdown yields 9,239 DR16Q hi-z quasars displayed, with 159 legacy citations.
• New DR16 pipeline quasars (z ≥ 1) identified as reliable include 2,330, with 284 hi-z among them and 268 confirmed as OK hi-z quasars after visual inspection.