* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Cosmology News -> Voids
Post Info TOPIC: Voids
Blobrana


L

Posts: 131433
Date:
Cosmic voids
Permalink  
 

Title: Voids in massive neutrino cosmologies
Author: Elena Massara, Francisco Villaescusa-Navarro, Matteo Viel, P. M. Sutter

Cosmic voids are a promising environment to characterise neutrino-induced effects on the large-scale distribution of matter in the universe. We perform a comprehensive numerical study of the statistical properties of voids, identified both in the matter and galaxy distributions, in massive and massless neutrino cosmologies. The matter density field is obtained by running several independent N-body simulations with cold dark matter and neutrino particles, while the galaxy catalogues are modelled by populating the dark matter halos in simulations via a halo occupation distribution (HOD) model to reproduce the clustering properties observed by the Sloan Digital Sky Survey (SDSS) II Data Release 7. We focus on the impact of massive neutrinos on the following void statistical properties: number density, ellipticities, two-point statistics, density and velocity profiles. Considering the matter density field, we find that voids in massive neutrino cosmologies are less evolved than those in the corresponding massless neutrinos case: there is a larger number of small voids and a smaller number of large ones, their profiles are less evacuated, and they present a lower wall at the edge. Moreover, the degeneracy between sigma_8 and Omega_nu is broken when looking at void properties. In terms of the galaxy density field, we find that differences among cosmologies are difficult to detect because of the small number of galaxy voids in the simulations. Differences are instead present when looking at the matter density and velocity profiles around these voids.

Read more (2031kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: Voids
Permalink  
 

Title: A Possible Cold Imprint of Voids on the Microwave Background Radiation
Author: Yan-Chuan Cai (Durham), Mark C. Neyrinck (JHU), Istvan Szapudi (IfA Hawaii), Shaun Cole (Durham), Carlos S. Frenk (Durham)

We measure the average temperature decrement on the cosmic microwave background (CMB) produced by voids selected in the SDSS DR7 spectroscopic redshift galaxy catalog, spanning redshifts 0<z<0.44. We find an imprint of amplitude between 2.6 and 2.9K as viewed through a compensated top-hat filter scaled to the radius of each void; we assess the statistical significance of the imprint at ~2sigma. We make crucial use of N-body simulations to calibrate our analysis. As expected, we find that large voids produce cold spots on the CMB through the Integrated Sachs-Wolfe (ISW) effect. However, we also find that small voids in the halo density field produce hot spots, because they reside in contracting, larger-scale overdense regions. This is an important effect to consider when stacking CMB imprints from voids of different radius. We have found that the same filter radius that gives the largest ISW signal in simulations also yields close to the largest detected signal in the observations. However, although it is low in significance, our measured signal is much higher-amplitude than expected from ISW in the concordance deltaCDM universe. The discrepancy is also at the ~2sigma level. We have demonstrated that our result is robust against the varying of thresholds over a wide range.

Read more (180kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Alignments of Voids in the Cosmic Web
Authors: Erwin Platen, Rien van de Weygaert, Bernard J.T. Jones

We investigate the shapes and mutual alignment of voids in the large scale matter distribution of a LCDM cosmology simulation. The voids are identified using the novel WVF void finder technique. The identified voids are quite nonspherical and slightly prolate, with axis ratios in the order of c:b:a approx. 0.5:0.7:1. Their orientations are strongly correlated with significant alignments spanning scales >30 Mpc/h.
We also find an intimate link between the cosmic tidal field and the void orientations. Over a very wide range of scales we find a coherent and strong alignment of the voids with the tidal field computed from the smoothed density distribution. This orientation-tide alignment remains significant on scales exceeding twice the typical void size, which shows that the long range external field is responsible for the alignment of the voids. This confirms the view that the large scale tidal force field is the main agent for the large scale spatial organisation of the Cosmic Web.

Read more (335kb, PDF)

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Cosmology News -> Voids


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard