The Mayall z-band Legacy Survey (MzLS) covers ~5000 deg² in the z band to depth of z=23.0.
The ninth data release (DR9) includes the entire MzLS footprint of ~5300 deg2 in the z band. DR9-north contains MzLS images taken between 19th November 2015 through 12th February 2018, and supersedes DR8 and previous MzLS releases. While no new data were added between DR8 and DR9, the data processing and photometry extraction were improved.
The observations are taken with MOSAIC on the Mayall telescope in three passes at each sky location. "Pass 1" is observed in photometric, good-seeing conditions. "Pass 2" and "Pass 3" are observed in progressively worse conditions. This strategy was adopted to ensure a photometric solution across the full survey area. The observing time is adjusted as a function of sky brightness and transparency.
Single exposures reach 5-sigma point source depth of 23.04 (pass 1), 22.95 (pass 2), and 22.85 (pass 3).
Unique area is resolved by including the BASS and MzLS images (from DR9-north) if they are both at Declination > 32.375° and north of the Galactic Plane. Otherwise, the DECam images (from DR9-south) are used. This method eliminates the overlap when combining the North and South areas into the full DR9 footprint.