A Thin Disc Galaxy: NGC3198

Not a point source, extending over 200,000 light years across.
Outside the core region

Velocity is constant at 150,000 m/s.
Mass density decreases exponentially,
mass/area = 37 Exp (-R'/2.23') solar masses/pc².
Total mass is 1.0 x 10⁴⁰ kg.

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sweetser@alum.mit.edu