The Linearity of the Cosmic Expansion Field from 300 to 30,000 km/s and the Bulk Motion of the Local Supercluster with Respect to the CMB

TL;DR

This study confirms the linearity of cosmic expansion from 300 to 30,000 km/s using precise distance measurements, and analyzes the Local Supercluster's motion relative to the CMB, finding it consistent with gravitational influences.

Contribution

It provides a detailed analysis of the linearity of cosmic expansion over a large velocity range and refutes the existence of a proposed Hubble Bubble at high confidence.

Findings

Cosmic expansion is linear within 2.3% over the studied velocity range.

The Local Supercluster moves at 448 km/s towards the CMB pole.

No evidence supports the proposed Hubble Bubble at 4 sigma confidence.

Abstract

The meaning of "linear expansion" is explained. Particularly accurate relative distances are compiled and homogenized a) for 246 SNe Ia and 35 clusters with v<30,000 km/s, and b) for relatively nearby galaxies with 176 TRGB and 30 Cepheid distances. The 487 objects define a tight Hubble diagram from 300-30,000 km/s implying individual distance errors of <7.5%. Here the velocities are corrected for Virgocentric steaming (locally 220 km/s) and - if v_220>3500 km/s - for a 495 km/s motion of the Local Supercluster towards the warm CMB pole at l=275, b=12; local peculiar motions are averaged out by large numbers. A test for linear expansion shows that the corrected velocities increase with distance as predicted by a standard model with q_0=-0.55 [corresponding to (Omega_M, Omega_Lambda)=(0.3,0.7)], but the same holds - due to the distance limitation of the present sample - for a range of models with q_0 between ~0.00 and -1.00. For these models H_0 does not vary systematically by more than +/-2.3% over the entire range. Local, distance-dependent variations are equally limited to 2.3% on average. In particular the proposed Hubble Bubble of Zehavi et al. and Jha et al. is rejected at the 4sigma level. - Velocity residuals in function of the angle from the CMB pole yield a satisfactory apex velocity of 448+/-73 km/s and a coherence radius of the Local Supercluster of ~3500 km/s (~56 Mpc), beyond which galaxies are seen on average at rest in co-moving coordinates with respect to the CMB. Since no obvious single accelerator of the Local Supercluster exists in the direction of the CMB dipole its motion must be due to the integral gravitational force of all surrounding structures. Most of the gravitational dipole comes probably from within 5000 km/s.