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Quaia, the Gaia-unWISE quasar catalog: an all-sky spectroscopic quasar sample

Storey-Fisher, Kate, Hogg, David W., Rix, Hans-Walter, Eilers, Anna-Christina, Fabbian, Giulio ORCID:, Blanton, Michael R. and Alonso, David 2024. Quaia, the Gaia-unWISE quasar catalog: an all-sky spectroscopic quasar sample. Astrophysical Journal 964 , 69. 10.3847/1538-4357/ad1328

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We present a new, all-sky quasar catalog, Quaia, that samples the largest comoving volume of any existing spectroscopic quasar sample. The catalog draws on the 6,649,162 quasar candidates identified by the Gaia mission that have redshift estimates from the space observatory’s low-resolution blue photometer/red photometer spectra. This initial sample is highly homogeneous and complete, but has low purity, and 18% of even the bright (G < 20.0) confirmed quasars have discrepant redshift estimates (∣Δz/(1 + z)∣ > 0.2) compared to those from the Sloan Digital Sky Survey (SDSS). In this work, we combine the Gaia candidates with unWISE infrared data (based on the Wide-field Infrared Survey Explorer survey) to construct a catalog useful for cosmological and astrophysical quasar studies. We apply cuts based on proper motions and colors, reducing the number of contaminants by approximately four times. We improve the redshifts by training a k-Nearest Neighbor model on SDSS redshifts, and achieve estimates on the G < 20.0 sample with only 6% (10%) catastrophic errors with ∣Δz/(1 + z)∣ > 0.2 (0.1), a reduction of approximately three times (approximately two times) compared to the Gaia redshifts. The final catalog has 1,295,502 quasars with G < 20.5, and 755,850 candidates in an even cleaner G < 20.0 sample, with accompanying rigorous selection function models. We compare Quaia to existing quasar catalogs, showing that its large effective volume makes it a highly competitive sample for cosmological large-scale structure analyses. The catalog is publicly available at 10.5281/zenodo.10403370.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Additional Information: License information from Publisher: LICENSE 1: URL:, Type: cc-by
Publisher: American Astronomical Society
ISSN: 0004-637X
Date of First Compliant Deposit: 19 March 2024
Date of Acceptance: 5 December 2023
Last Modified: 19 Mar 2024 10:00

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