Quaia: The Gaia-unWISE Quasar Catalog

Quaia is a quasar catalog constructed from the Gaia DR3 quasar candidates sample and unWISE infrared data. It is the largest-volume spectroscopic quasar catalog to date. The catalog is described in an associated publication, available at https://arxiv.org/abs/2306.17749 (Storey-Fisher et al. 2023, accepted to ApJ).

The files included are:

• quaia_G20.X.fits: The quasar catalog. Columns include the sky position, redshift estimate and uncertainty, Gaia and unWISE identifiers, Gaia and unWISE magnitudes, and proper motion values and uncertainties. The full format and column descriptions can be found in Table 2 of the paper linked above.
• selection_function_NSIDE64_G20.X.fits: The modeled selection function for the associated catalog, in the form of a healpixel map (NSIDE=64) with a value representing the relative probability that a source observed in that pixel would be included in the catalog. Note that these values are relative, and should not be interpreted directly as probabilities; see the paper for more details.
• random_G20.X_10x.fits: A random catalog generated with the associated selection function, having an initially Poisson sky distribution and then downsampled by the selection function map. The random has roughly 10 times the number of sources as the associated catalog.
• selection_function_template_maps.zip: A zipped set of the systematics templates used in the selection function fit, given as healpix maps with NSIDE=64. They are saved in numpy format and can be read with np.load. Each is named with map_<map_name>_NSIDE64.npy, where <map_name> is one of: dust, stars, unwise, m10, unwisescan, mcs, mcsunwise. These may be useful for certain applications of the catalog, such as additional checks of robustness to systematics.

These files are included for two versions of the catalog with different magnitude limits, denoted by the X's above: the full G<20.5 catalog contains 1,295,502 sources, and the G<20.0 version contains 755,850 sources (so X=0 or X=5). The G<20.0 version is cleaner and has overall better redshift estimates; it is just a subset of the G<20.5 catalog with an additional magnitude cut, but the associated selection function and random catalog are different so we provide it as a separate file for ease and clarity.

A notebook showing how to read in the files and visualize them is available at https://github.com/kstoreyf/gaia-quasars-lss/blob/main/notebooks/2023-10-08_data_products_inclzsplit.ipynb.