Tidal Influence on Satellite Shapes

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Session 108 -- Dwarf and Irregular Galaxies
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[108.14] Tidal Influence on Satellite Shapes

K. Long (SUNY at Brockport, U. Mass.), M.D. Weinberg (U. Mass.)

\noindent The structures of satellite systems, such as dwarf galaxies and globular clusters, are influenced by the tidal field of the Galaxy has well as internal dynamical processes. In this paper, we investigate the effect of the Galactic tidal field upon the shape and figure rotation of a satellite.

\smallskip \noindent We consider a satellite that is initially aspherical, and whose figure rotation is not synchronized with its orbit about the Galaxy. The aspherical shape must be supported by ``box'' orbits; if the tidal field is not phase-locked with the satellite, tidal torques may disrupt the box orbits and therefore destroy the asphericity of the satellite. We ask if tides can act to ``round'' a satellite by destroying box orbits, without disrupting the entire system.

\smallskip \noindent We have carried out N-body simulations of aspherical satellites in a tidal field. We find that the rounding process is efficient above a critical tidal field strength, sufficiently low that the entire system is not disrupted. We also find that phase-locking of the satellite's rotation occurs quickly in tidal fields below the critical strength for rounding, but does not occur in stronger tidal fields.

\smallskip \noindent It may be possible to use these results to constrain the masses of aspherical dwarf galaxies, by requiring that the tidal field they experience be below the critical field strength for rounding.

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