An Automatic Method and Comprehensive Analysis of Inter-Waveband Pixel Alignment Across the Sloan Digital Sky Survey

Comparing a galaxy’s structure across multiple wavebands may require high spatial resolution. For example, determining the color gradient across a spiral arm may allow us to ascertain the co-rotation radius, which can in turn inform theoretical considerations on arm formation and evolution. However, pixels in the Sloan Digital Sky Survey are not precisely aligned across wavebands, making unbiased pixel-resolution comparisons difficult. Since foreground stars are effectively point sources, their location can be determined to sub-pixel precision by fitting their light profiles to an appropriate point spread function. Here we describe a completely automated method that uses foreground stars in the Sloan Digital Sky Survey to align images of galaxies across wavebands to about 0.02 pixels. We have applied the method to the approximately 900,000 galaxies collected from the Galaxy Zoo 1 project. The technique is not specific to the Sloan Digital Sky Survey and could be easily adaptable to other surveys, provided they only require translation for alignment. We have made all source code and aligned images publicly available.