# High redshift galaxies in the HUDF

In the Hubble Ultra Deep Field ( http://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field ) there are almost 10.000 galaxies and some of them with redshift Z>6 . Making some approximations i need to compute the number of galaxies with redshift z = 7.

If the source density ( number / arcmin^2 ) at z=7 is given by,

$$\Sigma( > SFR ) = 10 ( SFR )^{-2.1}$$

and the relation between star formation rate and the rest frame UV luminosity is given by,

$$SFR = 1.4 10^{-28} L_{UV}$$

The relation between luminosity and flux density is,

$$f_v =\frac{L_v (1+z)}{4 \pi d_l^2}$$

and finally the minimum luminosity observed for an exposure time for a given filter is given

$$f = f_1 t_{exp}^{-1/2}$$

Given that information how can i design a survey that is targeting 100 galaxies with redshift z=7 and how could i minimize the exposure time , by taking single band imaging of the rest frame UV. Any ideas ?