On galaxy formation in asymmetric dark haloes
Abstract
The possible consequences of asymmetry in dark galactic haloes for galaxy formation are examined. It is argued that it is quite plausible that haloes indeed form with significant asymmetry. To make a preliminary but analytical study, the protogalactic collapse is idealized as a pressureless, test particle collapse of gas rotating initially as a solid body, in a rigid uniform density triaxial halo. The protogalaxy first forms a caustic sheet essentially normal to the halo's short axis, almost conserving its angular momentum (L). It is shown that, if the protogalaxy thereafter collapses as a thin sheet (due to efficient cooling of gas) which rotates about an axis in its plane, then it can lose a significant amount of its initial angular momentum (L_0_) to the dark halo. When L_0_ lies in the plane of the longest and middle axes of the halo this configuration of large L loss is achieved. Further, the greatest (~50-100 per cent) loss of L occurs for L_0_ parallel to the middle axis, The loss of L is also greater for collapse within more oblate haloes. It is speculated that elliptical galaxies form when a protogalaxy collapsing within an asymmetric halo loses most of its initial angular momentum to the halo. Asymmetric halo cores may also lead to bulges with anisotrpic velocity dispersion and assist the formation of central bars and compact objects.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 1988
- DOI:
- 10.1093/mnras/234.2.459
- Bibcode:
- 1988MNRAS.234..459S
- Keywords:
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- Dark Matter;
- Elliptical Galaxies;
- Galactic Evolution;
- Gravitational Collapse;
- Halos;
- Angular Momentum;
- Galactic Clusters;
- Galactic Nuclei;
- Astrophysics