The 6dF Galaxy Survey: cosmological constraints from the velocity power spectrum

I describe a new Bayesian based algorithm to infer the full three dimensional velocity field from observed distances and spectroscopic galaxy catalogues. In addition to the velocity field itself, the algorithm reconstructs true distances, some cosmological parameters and specific non-linearities in the velocity field. The algorithm takes care of selection effects, miscalibration issues and can be easily extended to handle direct fitting of, e.g., the inverse Tully-Fisher relation. I first describe the algorithm in details alongside its performances. This algorithm is implemented in the VIRBIuS (VelocIty Reconstruction using Bayesian Inference Software) software package. I then test it on different mock distance catalogues with a varying complexity of observational issues. The model proved to give robust measurement of velocities for mock catalogues of 3,000 galaxies. I expect the core of the algorithm to scale to tens of thousands galaxies. It holds the promises of giving a better handle on future large and deep distance surveys for which individual errors on distance would impede velocity field inference.

Section: The Flow Modelmentioning

confidence: 99%

“…These elements are parts of VIRBIuS, but they are generalized and included in a wider framework. I note that Johnson et al (2014) have also pushed the effort of measuring accurately velocity field. In all the aforementioned work however, a common framework to handle all components self-consistently are not included.…”

Section: Introductionmentioning

confidence: 99%

Bayesian 3D velocity field reconstruction with virbius

Lavaux

2016

“…This analytic solution for the window function was presented by Ma, Gordon & Feldman (2011). For further details on this calculation we refer the reader to Johnson et al (2014). We perform a full likelihood calculation using the 6dFGSv peculiar velocity sample (Springob et al 2014).…”

Section: Greene 2006)mentioning

confidence: 99%

“…Using the best-fit parameters from Set 4, we measure χ 2 6dFGSv = 778 with 979 data points: the full 6dfGSv velocity field is smoothed onto a grid with 979 nonempty elements (cf. Johnson et al 2014). …”

Section: Parameter Fits: Model Imentioning

confidence: 99%

Searching for modified gravity: scale and redshift dependent constraints from galaxy peculiar velocities

Johnson

Blake

Dossett

et al. 2016

Self Cite

We present measurements of both scale-and time-dependent deviations from the standard gravitational field equations. These late-time modifications are introduced separately for relativistic and non-relativistic particles, by way of the parameters G matter (k, z) and G light (k, z) using two bins in both scale and time, with transition wavenumber 0.01 Mpc −1 and redshift 1. We emphasize the use of two dynamical probes to constrain this set of parameters, galaxy power spectrum multipoles and the direct peculiar velocity power spectrum, which probe fluctuations on different scales. The multipole measurements are derived from the WiggleZ and BOSS Data Release 11 CMASS galaxy redshift surveys and the velocity power spectrum is measured from the velocity sub-sample of the 6-degree Field Galaxy Survey. We combine with additional cosmological probes including baryon acoustic oscillations, Type Ia SNe, the cosmic microwave background (CMB), lensing of the CMB, and the temperaturegalaxy cross-correlation. Using a Markov Chain Monte Carlo likelihood analysis, we find the inferred best-fit parameter values of G matter (k, z) and G light (k, z) to be consistent with the standard model at the 95% confidence level. Furthermore, accounting for the Alcock-Paczynski effect, we perform joint fits for the expansion history and growth index gamma; we measure γ = 0.665 ± 0.0669 (68% C.L) for a fixed expansion history, and γ = 0.73 +0.08 −0.10 (68% C.L) when the expansion history is allowed to deviate from ΛCDM. With a fixed expansion history the inferred value is consistent with GR at the 95% C.L; alternatively, a 2σ tension is observed when the expansion history is not fixed, this tension is worsened by the combination of growth and SNe data.

“…Comparing the galaxy-galaxy, galaxy-velocity and velocity-velocity power spectra (Johnson et al 2014) can lead to cosmological parameters, such as the redshift space distortion β and the correlation between galaxies and dark matter rg, that are degenerated when only the information provided by redshift surveys is used.…”

Section: Peculiar Velocitiesmentioning

confidence: 99%

The Low Redshift survey at Calar Alto (LoRCA)

Comparat

Chuang

Rodríguez-Torres

et al. 2016

The Baryon Acoustic Oscillation (BAO) feature in the power spectrum of galaxies provides a standard ruler to measure the accelerated expansion of the Universe. To extract all available information about dark energy, it is necessary to measure a standard ruler in the local, z < 0.2, universe where dark energy dominates most the energy density of the Universe. Though the volume available in the local universe is limited, it is just big enough to measure accurately the long 100 h −1 Mpc wave-mode of the BAO. Using cosmological N -body simulations and approximate methods based on Lagrangian perturbation theory, we construct a suite of a thousand light-cones to evaluate the precision at which one can measure the BAO standard ruler in the local universe. We find that using the most massive galaxies on the full sky (34,000 deg 2 ), i.e. a K 2MASS < 14 magnitude-limited sample, one can measure the BAO scale up to a precision of 4% (∼ 1.2% using reconstruction). We also find that such a survey would help to detect the dynamics of dark energy. Therefore, we propose a 3-year long observational project, named the Low Redshift survey at Calar Alto (LoRCA), to observe spectroscopically about 200,000 galaxies in the northern sky to contribute to the construction of aforementioned galaxy sample. The suite of light-cones is made available to the public.