Kate Storey-Fisher, David W. Hogg, Hans-Walter Rix, Anna-Christina Eilers, Giulio Fabbian, Michael Blanton, David Alonso
We present a new, all-sky quasar catalog, Quaia, that samples the largest comoving volume and has the cleanest selection function 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 BP/RP 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 Gaia and unWISE colors, reducing the number of contaminants by ∼4×. We improve the redshifts by training a k-nearest neighbors model on colors and Gaia redshift estimates and using SDSS redshift labels, and achieve redshift estimates on the G<20.0 sample with only 6% (10%) catastrophic errors with |Δz/(1+z)|>0.2 (0.1), a reduction of ∼3× (∼2×) compared to the Gaia redshifts. The final catalog has 1,295,502 quasars with a G<20.5, and 755,850 candidates in an even cleaner G<20.0 sample. We also construct a rigorous all-sky selection function model for the catalog. We compare Quaia to existing quasar catalogs, in particular showing that its large effective volume makes it a highly competitive sample for cosmological large-scale structure analyses. The catalog is publicly available at this https URL.
Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
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