Tilted Lema\^itre model and the dark flow

TL;DR

This paper proposes a tilted Lemaître cosmological model to explain the observed dark flow, a coherent large-scale motion of galaxy clusters relative to the CMB, by incorporating peculiar velocities increasing linearly with distance.

Contribution

It introduces a novel tilted Lemaître model that accounts for the dark flow through a linear velocity increase, linking it to intrinsic dipole effects in the Hubble law.

Findings

The model explains the dark flow as a linear increase of peculiar velocities with distance.

It relates the dark flow to the intrinsic dipole caused by kinematic acceleration.

The model treats radiation as a perfect fluid and matter as an imperfect fluid with heat flux.

Abstract

In the last years, the peculiar velocities of many X-ray galaxies clusters with respect to the distance have been measured directly in the rest frame of the cosmic microwave background radiation (CBR), using the kinematic Sunyaev-Zeldovich (kSZ) effect. These measures prove that exists a highly coherent motion, extending out to at least to ~1 Gpc, of the matter rest frame with respect to the CBR rest frame. This global motion was named "dark flow". By using an inhomogeneous spherically symmetric "tilted" Lema\^itre model, we could explain the dark flow if we assume a linear increase with distance of the peculiar velocities, which is in principle allowed by these observations. This linear increase of the dark flow with the distance has the same behavior that the intrinsic dipole, due to the kinematic acceleration, which appears in the Hubble law of the Lema\^itre model. In the "tilted" Lema\^itre model considered, we consider that the radiation orthogonal congruence is a perfect fluid and the matter "tilted" congruence is an imperfect fluid with heat flux.