The deceleration parameter in `tilted' Friedmann universes: Newtonian vs relativistic treatment

Understand

Although bulk peculiar motions are commonplace in the universe, most theoretical studies either bypass them, or take the viewpoint of the idealised Hubble-flow observers.

• As a result, the role of these peculiar flows remains largely unaccounted for, despite the fact that relative-motion effects have led to the misinterpretation of the observations in a number of occasions.
• Here, we examine the implications of large-scale peculiar flows for the interpretation of the deceleration parameter.
• We compare, in particular, the deceleration parameters measured by the Hubble-flow observers and by their bulk-flow counterparts.