Peculiar velocity
Peculiar motion or peculiar velocity refers to the velocity of an object relative to a rest frame — usually a frame in which the average velocity of some objects is zero.
Galactic astronomy
In galactic astronomy, peculiar motion refers to the motion of an object (usually a star) relative to a Galactic rest frame.
Local objects are commonly examined as to their vectors of
Cosmology
In physical cosmology, peculiar velocity refers to the components of a galaxy's velocity that deviate from the Hubble flow. According to Hubble's Law, galaxies recede from us at speeds proportional to their distance from us.
Galaxies are not distributed evenly throughout observable space, but are typically found in groups or
which is approximately
for low velocities (small redshifts). This combines with the redshift from the Hubble flow and the redshift from our own motion to give the observed redshift[3]
(There may also be a gravitational redshift to consider.[3])
The radial velocity of a cosmologically "close" object can be approximated by
with contributions from both the Hubble flow and peculiar velocity terms, where is the Hubble constant and is the distance to the object.
Redshift-space distortions can cause the spatial distributions of cosmological objects to appear elongated or flattened out, depending on the cause of the peculiar velocities.[4] Elongation, sometimes referred to as the "Fingers of God" effect, is caused by random thermal motion of objects; however, correlated peculiar velocities from gravitational infall are the cause of a flattening effect.[5] The main consequence is that, in determining the distance of a single galaxy, a possible error must be assumed. This error becomes smaller as distance increases. For example, in surveys of type Ia supernovae, peculiar velocities have a significant influence on measurements out to redshifts around 0.5, leading to errors of several percent when calculating cosmological parameters.[3][6]
Peculiar velocities can also contain useful information about the universe. The connection between correlated peculiar velocities and mass distribution has been suggested as a tool for determining constraints for cosmological parameters using peculiar velocity surveys.[7][8]
Bulk flow
The average of the peculiar velocity over a sphere is called the bulk flow. This value can be compared to theories of gravity. Current analysis of experimental bulk flow values are not in good agreement with the Lambda-CDM model.[9]
References
- ^ Schönrich, R.; Binney, J. (2010). "Local kinematics and the local standard of rest". .
- ^
Girardi, M.; Biviano, A.; Giuricin, G.; Mardirossian, F.; Mezzetti, M. (1993). "Velocity dispersions in galaxy clusters". doi:10.1086/172256.
- ^ a b c Davis, T. M.; Hui, L.; Frieman, J. A.; Haugbølle, T.; Kessler, R.; Sinclair, B.; Sollerman, J.; Bassett, B.; Marriner, J.; Mörtsell, E.; Nichol, R. C.; Richmond, M. W.; Sako, M.; Schneider, D. P.; Smith, M. (2011). "The Effect of Peculiar Velocities on Supernova Cosmology". .
- ^ Kaiser, N. (1987). "Clustering in real space and in redshift space". .
- ^
Percival, W. J.; Samushia, L.; Ross, A. J.; Shapiro, C.; Raccanelli, A. (2011). "Redshift-space distortions". PMID 22084293.
- ^ Sugiura, N.; Sugiyama, N.; Sasaki, M. (1999). "Anisotropies in Luminosity Distance". .
- ^
Odderskov, I.; Hannestad, S. (1 January 2017). "Measuring the velocity field from type Ia supernovae in an LSST-like sky survey". S2CID 119255726.
- ^
Weinberg, D. H.; Mortonson, M. J.; Eisenstein, D. J.; Hirata, C.; Riess, A. G.; Rozo, E. (2013). "Observational probes of cosmic acceleration". S2CID 119305962.
- arXiv:2310.16053.
See also
- Proper motion
- Radial velocity
- Relative velocity
- Space velocity (astronomy)