Second Data Release of the All-sky NOIRLab Source Catalog

We announce the second data release (DR2) of the NOIRLab Source Catalog (NSC), using 412,116 public images from CTIO-4 m+DECam, the KPNO-4 m+Mosaic3, and the Bok-2.3 m+90Prime. NSC DR2 contains over 3.9 billion unique objects, 68 billion individual source measurements, covers 35,000 square degrees of the sky, has depths of 23 mag in most broadband filters with 1%-2% photometric precision, and astrometric accuracy of 7 mas. Approximately 1.9 billion objects within 30,000 square degrees of sky have photometry in three or more bands. There are several improvements over NSC DR1. DR2 includes 156,662 (61%) more exposures extending over 2 more years than in DR1. The southern photometric zero-points in griz are more accurate by using the Skymapper DR1 and ATLAS-Ref2 catalogs, and improved extinction corrections were used for high-extinction regions. In addition, the astrometric accuracy is improved by taking advantage of Gaia DR2 proper motions when calibrating the astrometry of individual images. This improves the NSC proper motions to similar to 2.5 mas yr(-1) (precision) and similar to 0.2 mas yr(-1) (accuracy). The combination of sources into unique objects is performed using a DBSCAN algorithm and mean parameters per object (such as mean magnitudes, proper motion, etc.) are calculated more robustly with outlier rejection. Finally, eight multi-band photometric variability indices are calculated for each object and variable objects are flagged (23 million objects). NSC DR2 will be useful for exploring solar system objects, stellar streams, dwarf satellite galaxies, quasi-stellar objects, variable stars, high proper-motion stars, and transients. Several examples of these science use cases are presented. The NSC DR2 catalog is publicly available via the NOIRLab's Astro Data Lab science platform.

Automated summary

The second data release of the NOIRLab Source Catalog (NSC DR2) includes over 3.9 billion unique objects and 68 billion individual source measurements, covering a large area of the sky with improved accuracy and precision. With advancements in photometric and astrometric calibration, NSC DR2 will be valuable for studying various astronomical phenomena such as solar system objects, stellar streams, and variable stars.