MeerKAT Absorption Line Survey (MALS). I. DR1

Through comparisons with NVSS and FIRST at 1.4GHz, we establish the catalog's accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and 0.8", respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4GHz are in agreement with literature.

We estimate spectral indices ({alpha}) of a subset of 125621 sources (S/N>8), confirm the flattening of spectral indices with decreasing flux density, and identify 140 ultra-steep-spectrum ({alpha}{<}-1.3) sources as prospective high-z radio galaxies (z>2). We have identified 1308 variable and 122 transient radio sources comprising primarily active galactic nuclei that demonstrate long-term (26yr) variability in their observed flux densities.