Measuring the cosmological bulk flow using the peculiar velocities of supernovae

TL;DR

This study analyzes Type Ia supernovae data to detect large-scale cosmic bulk flow, finding a modest flow at low redshift consistent with the DM model, but no significant flow at higher redshifts.

Contribution

It provides a detailed analysis of bulk flow using supernovae data, highlighting differences between low and high redshift regimes and comparing results with previous studies.

Findings

Detected bulk flow at z < 0.05 with 95% confidence.

No significant bulk flow detected at z > 0.05.

Results are consistent with DM predictions.

Abstract

We study large-scale coherent motion in our universe using the existing Type IA supernovae data. If the recently observed bulk flow is real, then some imprint must be left on supernovae motion. We run a series of Monte Carlo Markov Chain runs in various redshift bins and find a sharp contrast between the z < 0.05 and z > 0.05 data. The$z < 0.05 data are consistent with the bulk flow in the direction (l,b)=({290^{+39}_{-31}}^{\circ}, {20^{+32}_{-32}}^{\circ}) with a magnitude of v_bulk = 188^{+119}_{-103} km/s at 68% confidence. The significance of detection (compared to the null hypothesis) is 95%. In contrast, z > 0.05 data (which contains 425 of the 557 supernovae in the Union2 data set) show no evidence for bulk flow. While the direction of the bulk flow agrees very well with previous studies, the magnitude is significantly smaller. For example, the Kashlinsky, et al.'s original bulk flow result of v_bulk > 600 km/s is inconsistent with our analysis at greater than 99.7% confidence level. Furthermore, our best-fit bulk flow velocity is consistent with the expectation for the \Lambda CDM model, which lies inside the 68% confidence limit.