Sparsely sampling the sky: Regular vs. random sampling

¹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
e-mail: p.paykari@ucl.ac.uk
² Laboratoire AIM, Irfu, Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
³ Department of Physics, Blackett Laboratory, Imperial College, London SW7 2AZ, UK

Received: 1 April 2015
Accepted: 20 June 2015

Abstract

Aims. The next generation of galaxy surveys, aiming to observe millions of galaxies, are expensive both in time and money. This raises questions regarding the optimal investment of this time and money for future surveys. In a previous work, we have shown that a sparse sampling strategy could be a powerful substitute for the – usually favoured – contiguous observation of the sky. In our previous paper, regular sparse sampling was investigated, where the sparse observed patches were regularly distributed on the sky. The regularity of the mask introduces a periodic pattern in the window function, which induces periodic correlations at specific scales.

Methods. In this paper, we use a Bayesian experimental design to investigate a “random” sparse sampling approach, where the observed patches are randomly distributed over the total sparsely sampled area.

Results. We find that in this setting, the induced correlation is evenly distributed amongst all scales as there is no preferred scale in the window function.

Conclusions. This is desirable when we are interested in any specific scale in the galaxy power spectrum, such as the matter-radiation equality scale. As the figure of merit shows, however, there is no preference between regular and random sampling to constrain the overall galaxy power spectrum and the cosmological parameters.