Are bulges of disk galaxies triaxial? Evidence from the photometry and the gas dynamics.

Details Are bulges of disk galaxies triaxial? Evidence from the photometry and the gas dynamics. Are bulges of disk galaxies triaxial? Evidence from the photometry and the gas dynamics.

Jun 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988msngr..52...24b&link_type=abstract

The Messenger, vol. 52, p. 24-27

Physics

7

Disk Galaxies:Gas Dynamics, Disk Galaxies:Photometry, Gas Dynamics:Disk Galaxies, Photometry:Disk Galaxies

Scientific paper

It is now generally accepted that elliptical galaxies are triaxial in shape. There are at least two strong observational hints that this is indeed the case: the first one is the well-known fact that elliptical galaxies are, normally, slow rotators (Bertola 1972; Bertola and Capaccioli 1975; IIlingworth 1977) whose shape is not due to rotation and therefore must be due to the flattening of their velocity dispersion ellipsoids. This makes it likely that the dispersion velocity tensor is flattened also along the intermediate axis, so that the resulting galaxy's figure is triaxial, rather than oblate. Secondly, elliptical galaxies show radial variations in ellipticity and position angle of their apparent major axis (Bertola and Galletta 1979). a phenomenon that cannot occur if their shape is prolate or oblate. This observational evidence is supported by theory: we know now that several galaxy-formation scenarios (Aarseth and Binney 1978; see also Lake, and White 1987 for reviews) exist where collapse of the proto- c1oud in its three main directions occurs on different timescales, making a triaxial object the most likely end-product of the scenario. Also, we know that tri axial stellar-dynamical models exist, which are stationary (except for perhaps a slow figure rotation), and stable to at least the grossest instabilities (Schwarzschild 1979).

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