المركز الإقليمي لتدريس علوم و تكنولوجيا الفضاء لغرب أسيا / الأمم المتحدة

Misshapen Space Voids Can Help Us Accurately Measure the Expansion of the Universe

“Experts have been able to use a new method to accurately measure the distortion caused byDoppler shifts on the shapes of voids – the way the light emitted by cosmic objects changes wavelength as they get closer to or further away from us – which in turn tells us more about how the Universe is expanding.”

The title of research paper:

“Beyond BAO: Improving cosmological constraints from BOSS data with measurement of the void-galaxy cross-correlation

Seshadri Nadathur, Paul M. Carter, Will J. Percival, Hans A. Winther, and Julian E. Bautista

Institute of Cosmology and Gravitation, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3FX, United Kingdom

Waterloo Centre for Astrophysics, Department of Physics and Astronomy, University of Waterloo, 200 University Ave W, Waterloo, Ontario N2L 3G1, Canada

Perimeter Institute for Theoretical Physics, 31 Caroline St. North, Waterloo, Ontario N2L 2Y5, Canada

Phys. Rev. D 100, 023504 – Published 9 July 2019

ABSTRACT

We present a measurement of the anisotropic void-galaxy cross-correlation function in the CMASS galaxy sample of the BOSS DR12 data release. We perform a joint fit to the data for redshift space distortions (RSD) due to galaxy peculiar velocities and anisotropies due to the Alcock-Paczynski (AP) effect, for the first time using a velocity field reconstruction technique to remove the complicating effects of RSD in the void center positions themselves. Fits to the void-galaxy function give a 1% measurement of the AP parameter combination

 D_A(z)H(z)/c=0.4367±0.0045 at redshift z=0.57, where D_A is the angular diameter distance and H the Hubble parameter, exceeding the precision obtainable from baryon acoustic oscillations (BAO) by a factor of ∼3.5 and free of systematic errors. From voids alone we also obtain a 10% measure of the growth rate, f_σ8(z=0.57)=0.501±0.051. The parameter degeneracies are orthogonal to those obtained from galaxy clustering. Combining void information with that from BAO and galaxy RSD in the same CMASS sample, we measure

 D_A(0.57)/r_s=9.383±0.077 (at 0.8% precision), H(0.57)r_s=(14.05±0.14)103  kms−1 Mpc−1 (1%), and f_σ8=0.453±0.022 (4.9%),

 consistent with cosmic microwave background (CMB) measurements from Planck. These represent a factor ∼2 improvement in precision over previous results through the inclusion of void information. Fitting a flat cosmological constant ΛCDM model to these results in combination with Planck CMB data, we find up to an 11% reduction in uncertainties on H_0 and Ω_m compared to use of the corresponding BOSS consensus values. Constraints on extended models with nonflat geometry and a dark energy of state that differs from w=−1show an even greater improvement.

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.023504

Draft version:

https://arxiv.org/pdf/1904.01030.pdf

https://www.sciencealert.com/voids-in-the-universe-can-help-measure-cosmic-expansion-more-accurately-than-ever?perpetual=yes&limitstart=1