Local Sheet

The Local Sheet or the Coma–Sculptor Cloud is a nearby galaxy filament and an extragalactic region of space where the Milky Way, the members of the Local Group, and other galaxies share a similar peculiar velocity.^[2] This region lies within a diameter of about 10.4 megaparsecs (34 million light-years; 3.2×10²⁰ kilometres), 465 kiloparsecs (1.52 million light-years; 1.43×10¹⁹ kilometres) 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 is only 40 km⋅s⁻¹ in the radial direction.^[2] Nearly all nearby bright galaxies belong to the Local Sheet.^[4] The Local Sheet is part of the Local Volume and is in the Virgo Supercluster (Local Supercluster).^[1] The Local Sheet forms a wall of galaxies delineating one boundary of the Local Void.^[5]

Local Sheet
A portion of the Local Sheet, the Council of Giants, on the top view within 10 million light-years from Earth, including the Local Group and other nearby giant galaxies.
Observation data (Epoch J2000)
Number of galaxies	14 (giant galaxies)[1]
Parent structure	Local Volume[1]
Major axis	33.9 Mly (10.4 Mpc)[1]
Minor axis	1.52 Mly (0.465 Mpc)[1]
Velocity dispersion	47 km/s[1]
Distance	420,700 ly (129 kpc) (center)[1]
ICM temperature	7.3×105 K[1]
Binding mass	1.6×1013[1] M☉
Other designations
Local Street, Coma–Sculptor Cloud[1]

The 14 major galaxies, including Milky Way and Andromeda Galaxies, of the Local Sheet

A significant component of the mean velocity of the galaxies in the Local Sheet appears as the result of the gravitational attraction of the Virgo Cluster of galaxies, resulting in a peculiar motion ~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).^[1]

The so-called Council of Giants is a ring of twelve large galaxies surrounding the Local Group in the Local Sheet, with a radius of 3.746 Mpc (12.22 Mly) and its center located at 810 kpc (2.6 Mly) away from the Sun.^[1] 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.

Galaxies in the "Council of Giants"^[1]

Catalog ID	Name	Constellation	Distance (Mly)	Stellar mass *
NGC 253	Sculptor Galaxy	Sculptor	11	10.805
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	11.169
NGC 4945		Centaurus	12	10.528
ESO 97-G13	Circinus Galaxy	Circinus	14	10.559

A portion of the Local Sheet within a map of 8 million light-years from Earth, including the Local Group and some other nearby galaxies.

* The mass is given as the logarithm (base unspecified) of the mass in solar masses.

Location

The Local Sheet is the co-moving part of the Coma-Sculptor Cloud,^[6] which was identified and described in 1987 by astronomer Brent Tully with colleague Richard Fisher in his book The Nearby Galaxies Atlas as Cloud 14.^[7] It is a huge 10 Mpc (33 Mly) prolate,^[8] filament^{[9][10][2][8]} and is mostly host to late-type galaxies, in contrast to the Virgo Cluster, in which more than half of the giant galaxies are early-type galaxies.^[11]

Tully maintains that the Coma-Sculptor Cloud and the Local Sheet do not quite overlap,^[2] as the Local Sheet comprises only the co-moving part of the Coma-Sculptor Cloud.^[6] McCall considers the two terms synonymous, referring to one and the same region.^[1]

See also

• Supergalactic coordinate system, the coordinate system taking the Local Sheet, the Supergalactic Plane, as its X–Y bases