Local Sheet

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The Local Sheet in astronomy is a nearby region of the observable universe where the Milky Way, the members of the Local Group and other galaxies share a similar peculiar velocity.[2] This region lies within a radius of about 7 Mpc (23 Mly),[3] 0.46 Mpc (1.5 Mly) thick,[1] and galaxies beyond that distance show markedly different velocities.[3] The Local Group has only a relatively small peculiar velocity of 66 km s−1 with respect to the Local Sheet. Typical velocity dispersion of galaxies within the Local Sheet is only 40 km s−1 in the radial direction.[2] All nearby bright galaxies belong to the Local Sheet.[1] The Local Sheet is part of the Local Volume and is in the Virgo Supercluster (Local Supercluster).[4]

A significant component of the mean velocity of the galaxies in the Local Sheet comes as the result of the gravitational attraction of the Virgo Cluster of galaxies. This results in a peculiar motion of about 185 km s−1 toward the cluster.[2] A second component is directed away from the center of the Local Void; an expanding region of space spanning an estimated 45 Mpc (150 Mly) that is only sparsely populated with galaxies.[3] This component has a velocity of 259 km s−1.[2] The Local Sheet is inclined 8° from the Local Supercluster (Virgo Supercluster).[4]

The Council of Giants is a ring of twelve large galaxies surrounding the Local Group in the Local Sheet, with a radius of 3.75 Mpc (12.2 Mly).[4] Ten of these are spirals, while the remaining two are ellipticals. The two ellipticals (Maffei 1 and Centaurus A) lie on opposite sides of the Local Group, and their formation may have prompted the development of the Local Group. The Local Sheet's own development outlines a concentration of dark matter in a filament.[1]

Galaxies in the "Council of Giants"
Catalog ID Name Constellation Distance (Mly) Mass *
PGC 9892 Maffei 1 Cassiopeia 11 10.928
PGC 10217 Maffei 2 Cassiopeia 11 10.493
IC 342   Camelopardalis 11 10.302
NGC 3031 M 81 Ursa Major 12 10.905
NGC 3034 M 82 Ursa Major 11 10.573
NGC 4736 M 94 Canes Venatici 15 10.458
NGC 4826 M 64 Coma Berenices 16 10.496
NGC 5236 M 83 Hydra 16 10.642
NGC 5128 Centaurus A Centaurus 11 10.528
NGC 4945   Centaurus 12 11.169
ESO 97-G13 Circinus Galaxy Circinus 14 10.559
NGC 253 Sculptor Galaxy Sculptor 11 10.805

* The mass is given as the log of the mass in solar masses.

References

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