11. The flux from a source with luminosity L will be S=L/(4.pi.D_L²). In the low z approximation, D_L scales as z[1+z(1-q₀)/2], and hence D_L² scales as z²[1+z(1-q₀)], i.e. as z² to first order. Hence, if L evolves as z³, then the flux will clearly rise with z.

If q₀ is negative, then at a given redshift D_L will be larger, so that objects will look less bright.