Measuring lineofsightdependent Fourierspace clustering using FFTs
Abstract
Observed galaxy clustering exhibits local transverse statistical isotropy around the line of sight (LOS). The variation of the LOS across a galaxy survey complicates the measurement of the observed clustering as a function of the angle to the LOS, as fast Fourier transforms (FFTs) based on Cartesian grids, cannot individually allow for this. Recent advances in methodology for calculating LOSdependent clustering in Fourier space include the realization that power spectrum LOSdependent moments can be constructed from sums over galaxies, based on approximating the LOS to each pair of galaxies by the LOS to one of them. We show that we can implement this method using multiple FFTs, each measuring the LOSweighted clustering along different axes. The Nlog N nature of FFTs means that the computational speedup is a factor of >1000 compared with summing over galaxies. This development should be beneficial for future projects such as DESI and Euclid which will provide an order of magnitude more galaxies than current surveys.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2015
 DOI:
 10.1093/mnrasl/slv090
 arXiv:
 arXiv:1505.05341
 Bibcode:
 2015MNRAS.453L..11B
 Keywords:

 cosmology: theory;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 5 pages, 2 figures, published in MNRAS