Density weighted angular redshift fluctuations: a new cosmological observable
Abstract
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 $\delta z (\hat{\mathbf {n}})$ consists of the statistics of sky maps built by projecting redshifts under a Gaussian window of width σ_{z} centred upon a redshift z_{obs}, and weighted by the galaxy density field. We compute the angular power spectrum of the $\delta z (\hat{\mathbf {n}})$ field in both numerical simulations and in linear perturbation theory. From these, we find that the $\delta z (\hat{\mathbf {n}})$ field (i) is sensitive to the underlying density and peculiar velocity fields; (ii) is highly correlated, at the $\gtrsim 60\, {{\ \rm per\ cent}}$ level, to the lineofsight projected peculiar velocity field; (iii) for narrow windows (σ_{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 redshiftindependent over ∼σ_{z}. We conclude that $\delta z (\hat{\mathbf {n}})$ 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.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 May 2021
 DOI:
 10.1093/mnrasl/slaa172
 arXiv:
 arXiv:1911.12056
 Bibcode:
 2021MNRAS.503L..56H
 Keywords:

 gravitation;
 cosmological parameters;
 theory;
 cosmology: largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 6 pages, 3 figures, matches accepted version in MNRAS letters, companion paper of ChavesMontero et al., arXiv:1911.10690