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.
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 position angle and radial velocity. These can be combined through vector addition to state the object's motion relative to the Sun. Velocities for local objects are sometimes reported with respect to the local standard of rest (LSR) – the average local motion of material in the galaxy – instead of the Sun's rest frame. Translating between the LSR and heliocentric rest frames requires the calculation of the Sun's peculiar velocity in the LSR.[1]
Cosmologyedit
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 clusters, where they have a significant gravitational effect one on another. Velocity dispersions of galaxies arising from this gravitational attraction are usually in the hundreds of kilometers per second, but they can rise to over 1000 km/s in rich clusters.[2] This velocity can alter the recessional velocity that would be expected from the Hubble flow and affect the observed redshift of objects via the relativistic Doppler effect. The Doppler redshift due to peculiar velocities is
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 flowedit
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]
^ Girardi, M.; Biviano, A.; Giuricin, G.; Mardirossian, F.; Mezzetti, M. (1993). "Velocity dispersions in galaxy clusters". The Astrophysical Journal. 404: 38–50. Bibcode:1993ApJ...404...38G. doi:10.1086/172256.
^ abc 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". The Astrophysical Journal. 741 (1): 67. arXiv:1012.2912. Bibcode:2011ApJ...741...67D. doi:10.1088/0004-637X/741/1/67.
^ Percival, W. J.; Samushia, L.; Ross, A. J.; Shapiro, C.; Raccanelli, A. (2011). "Redshift-space distortions". Philosophical Transactions of the Royal Society A. 369 (1957): 5058–5067. Bibcode:2011RSPTA.369.5058P. doi:10.1098/rsta.2011.0370. PMID 22084293.
^ Sugiura, N.; Sugiyama, N.; Sasaki, M. (1999). "Anisotropies in Luminosity Distance". Progress of Theoretical Physics. 101 (4): 903–922. Bibcode:1999PThPh.101..903S. doi:10.1143/ptp.101.903.
^ Odderskov, I.; Hannestad, S. (1 January 2017). "Measuring the velocity field from type Ia supernovae in an LSST-like sky survey". Journal of Cosmology and Astroparticle Physics. 2017 (1): 60. arXiv:1608.04446. Bibcode:2017JCAP...01..060O. doi:10.1088/1475-7516/2017/01/060. S2CID 119255726.
^ Weinberg, D. H.; Mortonson, M. J.; Eisenstein, D. J.; Hirata, C.; Riess, A. G.; Rozo, E. (2013). "Observational probes of cosmic acceleration". Physics Reports. 530 (2): 87–255. arXiv:1201.2434. Bibcode:2013PhR...530...87W. doi:10.1016/j.physrep.2013.05.001. S2CID 119305962.
^Said, Khaled (2023-10-24). "Tully-Fisher relation". In Di Valentino, E; Brout, D. (eds.). Hubble Constant Tension. arXiv:2310.16053.
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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 Contents 1 Galactic astronomy 2 Cosmology 2 1 Bulk flow 3 References 4 See alsoGalactic astronomy editIn 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 position angle and radial velocity These can be combined through vector addition to state the object s motion relative to the Sun Velocities for local objects are sometimes reported with respect to the local standard of rest LSR the average local motion of material in the galaxy instead of the Sun s rest frame Translating between the LSR and heliocentric rest frames requires the calculation of the Sun s peculiar velocity in the LSR 1 Cosmology editIn 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 clusters where they have a significant gravitational effect one on another Velocity dispersions of galaxies arising from this gravitational attraction are usually in the hundreds of kilometers per second but they can rise to over 1000 km s in rich clusters 2 This velocity can alter the recessional velocity that would be expected from the Hubble flow and affect the observed redshift of objects via the relativistic Doppler effect The Doppler redshift due to peculiar velocities is 1 z p e c 1 v c 1 v c displaystyle 1 z pec sqrt frac 1 v c 1 v c nbsp which is approximately z v c displaystyle z approx v c nbsp for low velocities small redshifts This combines with the redshift from the Hubble flow and the redshift from our own motion z displaystyle z odot nbsp to give the observed redshift 3 1 z o b s 1 z p e c 1 z H 1 z displaystyle 1 z obs 1 z pec 1 z H 1 z odot nbsp There may also be a gravitational redshift to consider 3 The radial velocity of a cosmologically close object can be approximated by v r H 0 d v p e c displaystyle v r H 0 d v pec nbsp with contributions from both the Hubble flow and peculiar velocity terms where H 0 displaystyle H 0 nbsp is the Hubble constant and d displaystyle d nbsp 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 edit 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 edit Schonrich R Binney J 2010 Local kinematics and the local standard of rest Monthly Notices of the Royal Astronomical Society 403 4 1829 1833 arXiv 0912 3693 Bibcode 2010MNRAS 403 1829S doi 10 1111 j 1365 2966 2010 16253 x Girardi M Biviano A Giuricin G Mardirossian F Mezzetti M 1993 Velocity dispersions in galaxy clusters The Astrophysical Journal 404 38 50 Bibcode 1993ApJ 404 38G doi 10 1086 172256 a b c Davis T M Hui L Frieman J A Haugbolle T Kessler R Sinclair B Sollerman J Bassett B Marriner J Mortsell E Nichol R C Richmond M W Sako M Schneider D P Smith M 2011 The Effect of Peculiar Velocities on Supernova Cosmology The Astrophysical Journal 741 1 67 arXiv 1012 2912 Bibcode 2011ApJ 741 67D doi 10 1088 0004 637X 741 1 67 Kaiser N 1987 Clustering in real space and in redshift space Monthly Notices of the Royal Astronomical Society 227 1 1 21 Bibcode 1987MNRAS 227 1K doi 10 1093 mnras 227 1 1 Percival W J Samushia L Ross A J Shapiro C Raccanelli A 2011 Redshift space distortions Philosophical Transactions of the Royal Society A 369 1957 5058 5067 Bibcode 2011RSPTA 369 5058P doi 10 1098 rsta 2011 0370 PMID 22084293 Sugiura N Sugiyama N Sasaki M 1999 Anisotropies in Luminosity Distance Progress of Theoretical Physics 101 4 903 922 Bibcode 1999PThPh 101 903S doi 10 1143 ptp 101 903 Odderskov I Hannestad S 1 January 2017 Measuring the velocity field from type Ia supernovae in an LSST like sky survey Journal of Cosmology and Astroparticle Physics 2017 1 60 arXiv 1608 04446 Bibcode 2017JCAP 01 060O doi 10 1088 1475 7516 2017 01 060 S2CID 119255726 Weinberg D H Mortonson M J Eisenstein D J Hirata C Riess A G Rozo E 2013 Observational probes of cosmic acceleration Physics Reports 530 2 87 255 arXiv 1201 2434 Bibcode 2013PhR 530 87W doi 10 1016 j physrep 2013 05 001 S2CID 119305962 Said Khaled 2023 10 24 Tully Fisher relation In Di Valentino E Brout D eds Hubble Constant Tension arXiv 2310 16053 See also edit nbsp Physics portal Proper motion Radial velocity Relative velocity Space velocity astronomy Retrieved from https en wikipedia org w index php title Peculiar velocity amp oldid 1192597030, wikipedia, wiki, book, books, library,
