Density weighted angular redshift fluctuations: a new cosmological observable

We propose the use of angular fluctuations in the galaxy redshift field as a new way to extract cosmological information in the Universe. This new probe delta z((n) over cap) consists of the statistics of sky maps built by projecting redshifts under a Gaussian window of width sigma(z) centred upon a redshift z(obs), and weighted by the galaxy density field. We compute the angular power spectrum of the delta z((n) over cap) field in both numerical simulations and in linear perturbation theory. From these, we find that the delta z((n) over cap) field (i) is sensitive to the underlying density and peculiar velocity fields; (ii) is highly correlated, at the >= 60 per cent level, to the line-of-sight projected peculiar velocity field; (iii) for narrow windows (sigma(z) < 0.03), it is almost completely uncorrelated to the projected galaxy angular density field under the same redshift window; and (iv) it is largely unaffected by multiplicative and additive systematic errors on the observed number of galaxies that are redshift-independent over similar to sigma(z). We conclude that delta z(<(n)over cap>) is a simple and robust tomographic measure of the cosmic density and velocity fields, complementary to angular clustering, that will contribute to more complete exploitations of current and upcoming galaxy redshift surveys.

Automated summary

The proposal introduces the use of angular fluctuations in the galaxy redshift field as a new way to extract cosmological information in the Universe. The new probe delta z((n) over cap) shows sensitivity to the density and peculiar velocity fields, as well as high correlation to the line-of-sight projected peculiar velocity field. It is concluded that delta z(<(n)over cap>) is a robust tomographic measure of the cosmic density and velocity fields that complements angular clustering in galaxy redshift surveys.