Image Construction

Galaxies that are comparable or larger than the 2MASS Atlas Image size (8X16 arcmin) require multiple image mosaicing. Due to the nature of 2MASS scans and background variations, this procedure is in practice very complicated. We take advantage of the fact that for images that belong to the same scan they will have correlated background structure due to atmospheric variations ("airglow" and clouds) along the scanning direction. Hence we first fit out the background for each scan, then fit the residuals across scans. The surface fit corresponds to a cubic polynomial, with a scale length that depends on the size of the target galaxy. The fitting procedure is roughly as follows:

More information on the fitting procedure, see the M33 and NGC 2903 constructions.