SMP on Lensing

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ASTC22. Lectures L21 Gravitational Lensing
SMP on Lensing (continued L20) Are these two
empirical laws similar? The same? Isothermal
spheres Isothermal distribution functions
Isothermal singular sphere Isothermal
non-singular sphere Conclusions for the
magnitude of dynamical friction in dark
halos the reason for efficient mergers
Rotation and flattening of elliptical galaxies
only a weak connection
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Tully-Fisher relationship, a correlation
between the luminosity and rotation for
disk galaxies
Log Vc
-2.5 log L
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Faber-Jackson relationship Luminosity sigma4
applies to ellipticals Tully-Fisher
relationship Luminosity (Vc)3.85 applies to
disk galaxies but the two are almost
identical both the disks and the ellipticals are
immersed in the same type of dark halos which
determines the maximum Vc via potential well
depth.
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(sorry, thats my teenage daughter)
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Good for modeling flat-Vc galaxies in dark halos
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...so this is one major reason why mergers of
galactic systems are so rapid (a few to a few
dozen periods)
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One more empirical correlation between rotation
and flattening of ellipticals, which can be
understood based on stellar dynamics
Fastest rotation according to theory
But remember theory gives the upper envelope
only. Most ellipticals are NOT supported or
flattened by rotation. They simply are not
relaxed flattening comes from initial
conditions, including geometry of encounter.