Measuring shapes of galaxy images -- I. Ellipticity and orientation
N. Rahman, Sergei F. Shandarin · Monthly Notices of the Royal Astronomical Society · 2003
We suggest a set of morphological measures that we believe can help in quantifying the shapes of two-dimensional cosmological images such as galaxies, clusters and superclusters of galaxies. The method employs non-parametric morphological descriptors known as the Minkowski functionals in combination with geometric moments widely used in the image analysis. For the purpose of visualization of the morphological properties of image contour lines, we introduce three auxiliary ellipses representing the vector and tensor Minkowski functionals. We study the discreteness, seeing and noise effects on elliptic contours as well as their morphological characteristics such as the ellipticity and orientation. In order to reduce the effect of noise, we employ a technique of contour smoothing. We test the method by studying simulated elliptic profiles of toy spheroidal galaxies ranging in ellipticity from E0 to E7. We then apply the method to real galaxies, including eight spheroidals, three disc spirals and one peculiar galaxy, as imaged in the near-infrared Ks-band (2.2 μm) with the Two Micron All Sky Survey. The method is numerically very efficient and can be used in the study of hundreds of thousands of images obtained in modern surveys.