Quaia, the Gaia-unWISE Quasar Catalog: An All-sky Spectroscopic Quasar Sample

Abstract

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.

Is the Radio Source Dipole from NVSS Consistent with the Cosmic Microwave Background and ΛCDM?

“…More detailed investigations of potential systematic effects in the measurements, additional modeling of the CatWISE samples, and other independent measurements with LSS tracers are essential further tests here. For example, the recent quasar catalog in Storey-Fisher et al (2024), constructed from a joint analysis with Gaia and unWISE, may be helpful in this regard.…”

Growth history and quasar bias evolution at z < 3 from Quaia

“…The Gaia-unWISE Quasar catalogue (Quaia hereafter) is a quasar sample that covers the entire sky and contains almost 1.3 million sources with magnitude G < 20.5. The catalogue, described in detail in [24], was obtained by combining the sample of quasar candidates in the third Gaia data release [29] together with infrared photometry from the unWISE reprocessing of the Wide-Field Infrared Survey Explorer (WISE) [30] to improve the purity of the sample and the quality of the redshift estimates. Quaia sources are assigned a spectrophotometric redshift estimated using a k-nearest neighbours algorithm that combines the Gaia-estimated spectroscopic redshift and photometry from both Gaia and unWISE.…”

“…This provides us with a better handle on growth evolution than the two bins used in [25], allowing us to also isolate the signal from the structure at z ∼ 3. The angular selection function for each of these bins was generated using the methodology described in [24]. We generate a projected overdensity map HEALPix 2 [32] for each redshift bin, defined as…”

“…Quasars, together with the Lyman-α forest, have provided our highest-redshift measurements of the redshift-distance relation via BAO [23], and they have been exploited to constrain large-scale cosmological observables, such as primordial non-Gaussianity, due to the enormous volumes they are able to probe. Recently, [24] presented Quaia, a quasar catalogue that covers almost the entire celestial sphere, constructed by combining the Gaia catalogue of quasar candidates with infrared photometry from unWISE. The availability of accurate and precise spectrophotometric redshifts allowed [25] to derive relatively tight constraints on ΛCDM from the auto-correlation of Quaia and its cross-correlation with CMB lensing maps from Planck.…”

Slant, Fan, and Narrow: The Response of Stellar Streams to a Tilting Galactic Disk

“…This is well below disk-tilting rates predicted by cosmological simulations, suggesting that Gaia astrometry should be sensitive enough to detect coherent motion of the stellar disk in excess of the usual galactic rotation. Recently, Storey-Fisher et al (2024) published a catalog of Gaiaand unWISE-selected quasars with proper-motion measurements. This catalog provides the necessary data set to begin searching for kinematic signatures of disk tilting, by anchoring the Gaia reference frame to the distant quasar sample.…”