Thick disk
The thick disk is one of the structural components of several galaxies, including the Milky Way. It was first proposed as a unique galactic structure, different from the thin disk and the halo in an 1983 article by Gilmore & Reid.[1] It is supposed to dominate the stellar number density between 1 to 5 kiloparsecs (3.3 to 16.3 kly) above the Galactic plane[1] and it's composed almost exclusively of older stars. Its chemical composition and kinematics (those of the stars comprising it) are also said to set it apart from the thin disk.[2][3]
The thick disk is a source of early kinematic and chemical evidence for a Galaxy's composition and thus is regarded as a very significant component for understanding Galaxy formation.
Origin
Various scenarios for the formation of this structure have been proposed, including:
- Thick disks come from the heating of the thin disk.[4]
- More energetic stars migrate outwards from the inner galaxy to form a thick disk at larger radii.[5]
- It is a result of a merger event between the Milky Way and another dwarf galaxy.[6]
Dispute
Although the thick disk is mentioned as a bona fide galactic structure in numerous scientific studies and it's even thought to be a common component of disk galaxies in general,[7] its existence is still under dispute.
A very recent study claims to give evidence that the Milky Way has a continuous and monotonic distribution of disk thicknesses which would imply that there is in fact no thick disk in the Galaxy.[8]
See also
- Thin Disk
- Galaxy formation and evolution
- Galactic coordinate system
- Galactic bulge
- Disc galaxy
- Spiral arm
- Galactic halo
References
- ↑ 1.0 1.1 Gilmore & Reid, 1983, "New light on faint stars. III - Galactic structure towards the South Pole and the Galactic thick disc",
- ↑ Bensby & Feltzing, "The Galactic thin and thick discs in the context of galaxy formation",
- ↑ Kordopatis et al., "A spectroscopic survey of thick disc stars outside the solar neighbourhood",
- ↑ Matthias Steinmetz, The Galactic thin and thick disk (2012), p. 4"
- ↑ Ken Freeman, Structure and Evolution of the Milky Way (2012), p. 4"
- ↑ Bensby et. al (1970). "The Galactic thin and thick discs in the context of galaxy formation". arXiv:0908.3807v1.pdf.
- ↑ Ken Freeman, Structure and Evolution of the Milky Way (2012), p. 4: "Thick disks are very common in disk galaxies."
- ↑ Bovy et al., "THE MILKY WAY HAS NO DISTINCT THICK DISK"
External links
- New light on faint stars III
- Thin and Thick Galactic Disks
- Structure and Evolution of the Milky Way
- Populations & Components of the Milky Way
- A spectroscopic survey of thick disc stars outside the solar neighbourhood