Bayesian cosmic density field inference from redshift space dark matter maps.

We present a self-consistent Bayesian formalism to sample the primordial density fields compatible with a set of dark matter density tracers after a cosmic evolution observed in redshift space. Previous works on density reconstruction did not self-consistently consider redshift space distortions or included an additional iterative distortion correction step. We present here the analytic solution of coherent flows within a Hamiltonian Monte Carlo posterior sampling of the primordial density field. We test our method within the Zel'dovich approximation, presenting also an analytic solution including tidal fields and spherical collapse on small scales. Our resulting reconstructed fields are isotropic and their power spectra are unbiased compared to the true field defined by our mock observations. Novel algorithmic implementations are introduced regarding the mass assignment kernels when defining the dark matter density field and optimization of the time-step in the Hamiltonian equations of motions. Our algorithm, dubbed barcode, promises to be specially suited for analysis of the dark matter cosmic web down to scales of a few megaparsecs. This large-scale structure is implied by the observed spatial distribution of galaxy clusters - such as obtained from X-ray, Sunyaev-Zel'dovich, or weak lensing surveys - as well as that of the intergalactic medium sampled by the Ly α forest or perhaps even by deep hydrogen intensity mapping. In these cases, virialized motions are negligible, and the tracers cannot be modelled as point-like objects. It could be used in all of these contexts as a baryon acoustic oscillation reconstruction algorithm.

Signatures of the Primordial Universe from Its Emptiness: Measurement of Baryon Acoustic Oscillations from Minima of the Density Field.

Sound waves from the primordial fluctuations of the Universe imprinted in the large-scale structure, called baryon acoustic oscillations (BAOs), can be used as standard rulers to measure the scale of the Universe. These oscillations have already been detected in the distribution of galaxies. Here we propose to measure BAOs from the troughs (minima) of the density field. Based on two sets of accurate mock halo catalogues with and without BAOs in the seed initial conditions, we demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but it is clearly detected from overlapping voids. The latter represent an estimate of all troughs of the density field. We compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models based on an unprecedented large set of detailed simulated void catalogues are remarkably well confirmed by observational data. We use the largest recently publicly available sample of luminous red galaxies from SDSS-III BOSS DR11 to unveil for the first time a >3σ BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their centers represent the most quiet places in the Universe, keeping in mind the cosmos origin and providing a new promising window in the analysis of the cosmological large-scale structure from galaxy surveys.