An Estimate of the Velocity Correlation Tensor: Cosmological Implications
Abstract
Using recent observations of large-scale motions, we estimate the peculiar velocity correlation tensor, ξalphaβ_(r) in the cosmic background radiation (CBR) frame. By studying random samples, we find that our method of estimating ξalphaβ_ is reliable for 500 km s^-1^ <~ Hr <~ 4000 km s^-1^. The data show significant structure in ξalphaβ_ well beyond this upper limit, suggesting that the velocity field is correlated over scales comparable to or larger than the sample depth and that the surveys analyzed here are too shallow to constitute a fair sample. The standard biased ({OMEGA}= 1, b = 2.5) cold dark matter scenario is inconsistent, at a statistically significant level, with the observed correlation functions in the CBR frame. The correlation functions predicted by this scenario differ significantly in both shape and amplitude from the observed ξalphaβ_. The discrepancy is consistent with that found in previous studies based on bulk flow and great attractor (GA) kinematic models. Unlike the CDM model, low {OMEGA}, baryon-dominated scenarios containing entropy perturbations can lead to correlated velocities over scales exceeding 4000 km s^-1^. Thus our estimate of ξalphaβ_ is in fact predicted to be dominated by sampling effects, and our analysis cannot test the viability of these scenarios. We also consider the velocity field in the local standard of rest (LSR) frame determined by the galaxies themselves. In this frame (or in one with the GA velocities removed) the correlation functions are much smaller but positive on scales Hr <~ 1000 km s^-1^, and slightly negative at Hr ~ 2000 km s^-1^. This residual, small velocity field can be interpreted in a manner consistent with the galaxy-galaxy correlation function. The signal at small scales may be produced by correlated pairs of galaxies in the same cluster which share the overall motion of the cluster while the negative signal at Hr ~ 2000 km s^-1^ may be due to infall onto newly forming clusters. In any case, the residual flow is much smaller than the large-scale flow which is mostly a translation and must arise from sources beyond the observed domain or from a misunderstanding of the microwave background.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1989
- DOI:
- 10.1086/168038
- Bibcode:
- 1989ApJ...346..558G
- Keywords:
-
- Cosmology;
- Galactic Clusters;
- Relic Radiation;
- Tensors;
- Velocity Distribution;
- Correlation;
- Dark Matter;
- Elliptical Galaxies;
- Galactic Evolution;
- Spiral Galaxies;
- Astrophysics;
- COSMIC BACKGROUND RADIATION;
- COSMOLOGY;
- GALAXIES: CLUSTERING