- Ingular Diameters 6 2 3 3 14 Marks For A Flat Universe Without A Cosmological Constant The Equation For The Angular D 1 (78.31 KiB) Viewed 207 times
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ingular diameters 6+2+3+3= 14 Marks For a flat universe, without a cosmological constant, the equation for the angular diameter of a galaxy as a function of redshift z, simplifies to DH (1+z)³/2 0 = 2c (1+z)¹/²-1 where D is the linear diameter of the galaxy. (a) Show that this function has a minimum value, and determine the redshift at which this occurs. (b) Explain why this happens. (c) Suppose that a galaxy has a radius of 15kpc, what would the minimum angular diameter of this galaxy be? Take Ho-70 km/(s.Mpc). (d) A galaxy does not have a well-defined optical edge, but has decreasing luminosity as a function of radius. Comment on whether this will affect the value obtained, and if so how.