24_-_Normal_Galaxies_2

# 24_-_Normal_Galaxies_2 - 24 Normal Galaxies(2 Perspective...

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24 - Normal Galaxies(2) Sandy Faber, USB Leader of the Seven Samurai 2 Perspective Dynamics of elliptical galaxies Cold Dark Matter and its varieties 3 Dynamics We know about the rotation curve of spirals but what about motions in elliptical galaxies? They look more like a swarm of bees rather than a rotating ball. The picture is even more mysterious. 4 Elliptical Galaxies in the Virgo Cluster M87 cD M84 M86

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5 M87 6 E0 to E7 En where n = 10(1-b/a) & 0 n 7 E 0 -> round (sphere or end on spindle?) E 7 -> spindle or frizbee a b 7 8
9 10 11 Surface Brightness Ellipticals have little dust, so to first order we see all of the starlight. Fitting laws: – I(R) = I e exp{-7.67[(R/R e ) 1/4 -1]} de Vaucouleur Half of the light is from inside R e – I(R) = I o /(1+R/R o ) 2 Hubble’s Law • R 0 is a fitting radius These functions are quite different mathematically but remarkably similar in shape. 12 De-projecting Galaxy’s Image ( ) 1 2 2 2 ( ) ( ) 2 ( ) R j r rdr I R j r dz r R -∞ = = - •The above is an integral equation where I is given and j is derived. •z is along the line of sight, r is the radius. •j(R) = emission/cm 3 = the light generated inside the galaxy. •R is the closest approach to the center. •But there is more to the puzzle.

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13 Take the derivative and integrate ( ) 1 2 2 2 1 ( ) r dI dR j r dR R r π = - - • This is called the Abel’s Integral equation. • The problem is that you are dealing with the derivative of the observed quantity. 14 How to Make a Galaxy in a Computer 1. Form a group of stars An initial mass function (Salpeter) is needed Define the 3-D distribution of mass, etc.
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