OGLE-ing the Magellanic System: Optical Reddening Maps of the Large and Small Magellanic Clouds from Red Clump Stars

We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670 deg² of the sky in the Magellanic System region. The resulting maps provide reddening information for 180 deg² in the Large Magellanic Cloud (LMC) and 75 deg² in the Small Magellanic Cloud (SMC), with a resolution of 1'7 × 1'7 in the central parts of the MCs, decreasing to approximately 27' × 27' in the outskirts. The mean reddening is E(V - I) = 0.100 ± 0.043 mag in the LMC and E(V - I) = 0.047 ± 0.025 mag in the SMC. We refine methods of calculating the RC color to obtain the highest possible accuracy of reddening maps based on RC stars. Using spectroscopy of red giants, we find the metallicity gradient in both MCs, which causes a slight decrease of the intrinsic RC color with distance from the galaxy center of ∼0.002 mag/deg in the LMC and between 0.003 and 0.009 mag/deg in the SMC. The central values of the intrinsic RC color are 0.886 and 0.877 mag in the LMC and SMC, respectively. The reddening map of the MCs is available both in downloadable form and as an interactive interface.