The Galaxy Octopole Moment as a Probe of Weak‐Lensing Shear Fields

In this paper, we introduce the octopole moment of the light distribution ingalaxies as a probe of the weak lensing shear field. While traditionalellipticity estimates of the local shear derived from the quadrupole moment arelimited by the width of the intrinsic ellipticity distribution of backgroundgalaxies, the dispersion in the intrinsic octopole distribution is expected tobe much smaller, implying that the signal from this higher order moment isultimately limited by measurement noise, and not by intrinsic scatter. Wepresent the computation of the octopole moment and show that currentobservations are at the regime where the octopole estimates will soon be ableto contribute to the overall accuracy of the estimates of local shear fields.Therefore, the prospects for this estimator from future datasets like theAdvanced Camera for Survey and the Next Generation Space Telescope are verypromising.Comment: 9 pages, 2 PostScript figures; Submitted to Astrophysical Journa